AHC Inop after fluid change 2007 lx C1751 and C1762

[suprarx7nut]

I emptied all 4 corners and accumulator. All of the bleeder is emptied. AHC fluid reservoir was full and then I topped it off. But none of the oil is going down it stayed at the same level. Accumulator pressure is at 0. No more fluid in there. Pump run for a bit then it stopped.

Looks like the pump is not building pressure.

1. It might help to explain the sequence of events. How many miles have you driven successfully since the flush?
2. Did you use fluid from the black liter bottles of AHC? There was a problem batch of that fluid that can gel up the pump and fail to get past the simple screen filters.

 

[Muhammad Rais]

Looks like the pump is not building pressure.

1. It might help to explain the sequence of events. How many miles have you driven successfully since the flush?

I drove around 2000 miles. I flushed it around August 2021. After the 1st flush I had a lot of bubbles then after 10 flushes I got rid of the bubbles and car was back to normal.

2. Did you use fluid from the black liter bottles of AHC? There was a problem batch of that fluid that can gel up the pump and fail to get past the simple screen filters.

Yes black plastic liter bottle from Toyota

 

[Muhammad Rais]

Looks like the pump is not building pressure.

1. It might help to explain the sequence of events. How many miles have you driven successfully since the flush?

I drove around 2000 miles. I flushed it around August 2021. After the 1st flush I had a lot of bubbles then after 10 flushes I got rid of the bubbles and car was back to normal.

2. Did you use fluid from the black liter bottles of AHC? There was a problem batch of that fluid that can gel up the pump and fail to get past the simple screen filters.

Yes black plastic liter bottle from Toyota

 

[IndroCruise]

I drove around 2000 miles. I flushed it around August 2021. After the 1st flush I had a lot of bubbles then after 10 flushes I got rid of the bubbles and car was back to normal.

Yes black plastic liter bottle from Toyota

On the current thread, I can see your long history of learning about the AHC/TEMS systems and eventually overcoming frustrations, starting around post #268 in this thread and running through to post #303 today. There has been a lot of input from IH8MUD Members.

If not already done, may I respectfully suggest, please refresh your understandings of previous issues and information by looking through all of those posts and attachments again? Especially this post in September 2021 – because it seems that you are almost back to the same situation as you were then.

New symptoms reported and some observations:

1. Your vehicle is 2000 Lexus LX470, now around 22 years old – and assume now around 250,000 miles travelled?

2. In August and September 2021, replaced AHC Fluid by bleeding, using AHC Fluid in 1 litre plastic bottles purchased from a Dealer at that time – after many efforts to remove air from the AHC system,

3. AHC and TEMS systems appeared to operate normally for five months until March 2022,

4. In March 2022, vehicle suddenly dropped to “LO” height setting while driving,

5. No leaks visible around the vehicle,

6. After returning home, used Techstream – see screenshots here.

7. Assume AHC Pump was working and an attempt was made to raise from “LO” to “N” to achieve the new Techstream measurements shown on the screenshot??? Please confirm. This is important!

8. The AHC pressures on the screenshot are:
AHC Front: 2.1 Mpa;
AHC Rear: 5.0 MPa;
Height Control Accumulator: 0.0 Mpa.
All of these pressures are very low,

9. It is not known whether the AHC Pressure Sensor is working correctly and giving reliable outputs – this the large Sensor located on the AHC Pump Assembly on the metal block between the AHC Pump and its Motor,

10. The AHC Fluid temperature on the screenshot is: 118 degrees Fahrenheit -- this could be a little high and may suggest that the AHC Pump was operating or attempting to operate?

11. If AHC Pump was not working, then the AHC pressure readings on the screenshot are old numbers remembered by the Electronic Control Unit (ECU) and are meaningless,

12. If AHC Pump was working, and if the Pressure Sensor is reliable, then the AHC pressure readings indicate that the AHC Pump could not develop enough pressure and flow to raise the vehicle from “LO” to “N” height. The AHC Pump also could not refill the Height Control Accumulator -- because the vehicle did not complete the raise,

13. There was no AHC Fluid from bleeding the Height Control Accumulator. This means that the Height Control Accumulator had not previously been filled by the AHC Pump, so the Height Control Accumulator is empty – does not contain any AHC Fluid to bleed (but it may contain air),

14. Diagnostic Trouble Code (DTC) 1751 is shown on the screenshot. This means “AHC Pump & Motor Circuit” have not completed the raise from “LO” to “N” within the time limits,

15. Diagnostic Trouble Code (DTC) 1762 is shown on the screenshot. This means “Fluid Pressure Abnormality (Pump & Motor Does Not Supply Fluid)”,

16. Diagnostic Trouble Code (DTC) 1718 is not shown on the screenshot. This means that the signal from the “Fluid Pressure Sensor Circuit” to the ECU circuit should be reliable (but testing is a good idea anyway),

17. Back at the end of post #283 in this thread, see attachments detailing the defined conditions for each of DTC 1718, DTC 1751 and DTC 1762, along with the testing procedures and recommended action if No Good (NG),

18. Given these DTC’s, the AHC system is not operating, has dropped to “LO” height, and is not raising correctly. This is not surprising, because ….

19. ALL of DTC 1718, DTC 1751 and DTC 1762 have a similar ‘fail-safe mode’ as stated in the FSM: “If trouble occurs, the height control is prohibited after adjusting the vehicle to the standard height in case that the height is higher than the standard or to the lowest wheel of the 4 wheels in case that the height is lower than the standard”,

20. When these DTC’s show up, it means that the AHC system DOES NOT WORK – and once the vehicle is at “LO” height the AHC system is PROHIBITED by the ECU from raising automatically, until the problem causing the DTC is fixed,

21. How can this happen ‘suddenly’? Actually, it does not happen suddenly. Like most things on vehicles, there will have been a slow deterioration towards the conditions which cause these DTC’s (again, see attachments at the bottom of post #283 in this thread) -- until one day the defined conditions eventually are reached and the ECU puts the AHC system into ‘fail-safe mode’ for its own protection and for vehicle safety,

22. Attempted to bleed AHC system with vehicle at “LO” and noticed that AHC Pump was not taking in AHC Fluid from the AHC Tank – again, not really surprising, as above,

23. Zooming into picture at post #299 on this thread shows that a LOT of air was in AHC Fluid which came out of the system during recent efforts at bleeding,

24. The Techstream screenshots at post #299 on this thread are the same as the screenshots mentioned at paragraph 6 above. [By the way, it is best to stick with one thread for the same problem on the same vehicle – it causes confusion to readers trying to solve the problem when parts of your story are on different threads],

25. None of the recent screenshots for this vehicle show Front and Rear AHC pressures in the expected range per the Factory Service Manual (FSM),

26. None of the recent screenshots for this vehicle show Height Control Accumulator pressure anywhere near the expected value of around 10.5 Mpa,


Interpretation of the above symptoms:

There are several possibilities, mostly involving air or nitrogen gas in this system. This can have only three causes. It is suggested that these causes should be considered in the following order:

(A). Nitrogen gas escaping from behind worn-out membranes in very old ‘globes’. [If the ‘globes’ on this 2000 Lexus LX470 are more than 10 years old or have failed the attached HI/LO Test, then the ‘globes’ should be replaced],

AND/OR

(B). Air entering the system when the fluid level in the AHC Tank drops too low, or if air leaks around the seal between the AHC Tank and the AHC Pump. [When this happens, air goes to all parts of the AHC system – ‘globes’, shock absorbers, Height Control Accumulator – and then requires multiple bleeding efforts to remove the air. The suggestion at post #295 in this thread is a good way of clearing air out of the Height Control Accumulator],

AND/OR

(C). The inlet filter/strainer at the AHC Pump is blocked with debris from within the AHC system, or, from gelatinous or waxy substances in faulty AHC Fluid. [When this happens on the inlet side of a gear pump such as the AHC Pump, then the pump is starved of fluid. Either ‘cavitation’ takes place and the pump operates roughly and noisily and eventually could damage itself, OR, ‘aeration’ occurs when air is drawn in past the seals around the pump – in this case, around the small O-ring at the AHC Pump inlet, or around the large O-ring at the outer cover of the pump. This only happens for a short time until the ECU recognises a low pressure signal from the Pressure Sensor and the ‘fail-safe’ function stops the AHC Pump from destroying itself – and records the relevant DTC’s. How to check and clean internal fliter/strainers in the AHC Pump and how to deal with AHC Pump replacement and costs are described at post #280 and post #294 in this thread].


Conclusions:

There is no happiness in starting with AHC Pump replacement and then finding later that the real problem was air or gas still trapped in the AHC system – so first be very sure of effective bleeding procedures and be very confident that all air and/or nitrogen gas have been eliminated.

When confident that air or nitrogen gas are not the problem, then it is time to investigate and replace the AHC Pump as described in earlier posts in this thread. After 22 years onboard a 2000 LX470, it is not too early and it is not expensive to replace the AHC Pump (if supplied by IMPEX or Partsouq). This will require a full re-bleeding of the system anyway.


Some further relevant information:

The “Active Test”:

The “Active Test” is used to check AHC operation.

It also can be used when it is desired to start an AHC Pump which has stopped and will not start automatically.

The main reason for such a stoppage is when air gets into the AHC Pump – such as during bleeding of the system, or if there is a poor seal between the AHC Tank and the AHC Pump, or at the O-rings within the AHC Pump assembly.

Air causes low pressure to be detected by the Pressure Sensor. The AHC Pump then stops for its own protection – it is not good for a gear pump to run without fluid for a long period.

The “Active Test” also can be used to start a pump when in ‘fail-safe’ mode while resolving the ‘fail-safe’ problem.

The “Active Test” can be done from the ‘Utility’ feature in Techstream, or, it can be done manually using the procedure below and at Section 5 of Page 6 of the “Pre-check” attachment.

The procedure should only be done for a short period of time -- about 10 seconds -- long enough to be sure that the pump is drawing fluid from the tank. This is called “priming” the pump:

1. With Ignition OFF, connect terminals Ts and E1 at DLC1 (this is the socket in the engine bay, usually over the RHS wheel arch with the word DIAGNOSTIC on the top cover. The terminal "map" is shown inside this cover. Instead of Special Service Tool (SST) 09843-18020 which is just a piece of bridging wire, find something simple -- I use an unbent paperclip for this test. Voltages here are low, about 4.5 volts, and will not cause a problem -- but be careful to connect the correct terminals,

2. Turn ON the engine.

3. Select “COMFORT” on the variable damping switch on the centre console,

4. Push the DOWN button on the Height Select switch within 5 seconds of engine start and hold it down for 5 seconds. There will many flashing lights in the instrument cluster (because the ECU functions are being by-passed). Ignore these -- they will revert to normal later, after the test, when the bridge (paperclip) is removed and the AHC ON/OFF switch is pressed down for a couple of seconds,

5. Use the combined settings to move front or rear up or down (listen for the operation of the AHC Pump and its motor),

6. When finished, switch OFF engine and switch OFF ignition, then remove the bridge (paperclip),

7. Re-start, push down and hold down the AHC ON/OFF for a couple of seconds to clear the test.


Height Control Accumulator problem before October 2002:

Vehicles manufactured before October 2002 are subject to possible failure of an O-ring inside the Height Control Accumulator. This O-ring cannot be replaced – see attached Technical Service Bulletin (TSB) CP-3006. [Aside: The TSB advises that the consequence is that this O-ring may break down and eventually find its way to the AHC Pump. At the AHC Pump this debris can clog one or both of the two small filter/strainers inside the AHC Pump. This is not the only possible cause of clogged AHC Pump filter/strainers. However caused, clogged filter/strainers at the AHC Pump will give rise to Diagnostic Trouble Codes (DTC’s) C1751 and C1762].

 

[blips]

I second the advice to use the active test to force the pump to run to get it primed after completely flushing. Also, it helps if you do this in temperatures above freezing. Cold weather can make the system sluggish.

Once you get the pump primed, try to raise the vehicle to N. It might take a long time. To prevent the vehicle from throwing a code for continuous current to pump motor you can let it go 30 seconds or so, then hit “off” and let it rest for thirty seconds. Keep doing this until you get the vehicle to N height and pressure back in the accumulator. Now, do a partial bleed (just a couple ounces from each bleeder until fluid runs clear, don’t go to the bump stops). Refill fluid, cycle to high, then low, and back to neutral. Repeat until you don’t get any more air bubbles and the system is back to normal.

PS, this worked for me after depressurizing the accumulator by powering the solenoid with a battery. My accumulator bleeder valve is broken off and I was attempting to install a new accumulator. Didn’t have the right crow foot flare nut wrenches so I decided to refill and roll with it as is for now. System kept throwing the low pressure code so the normal steps wouldn’t work. Active test and using the off button to suspend pump operation before the continuous pump code triggered were the key.

 

[Muhammad Rais]

On the current thread, I can see your long history of learning about the AHC/TEMS systems and eventually overcoming frustrations, starting around post #268 in this thread and running through to post #303 today. There has been a lot of input from IH8MUD Members.

If not already done, may I respectfully suggest, please refresh your understandings of previous issues and information by looking through all of those posts and attachments again? Especially this post in September 2021 – because it seems that you are almost back to the same situation as you were then.

New symptoms reported and some observations:

1. Your vehicle is 2000 Lexus LX470, now around 22 years old – and assume now around 250,000 miles travelled?

2. In August and September 2021, replaced AHC Fluid by bleeding, using AHC Fluid in 1 litre plastic bottles purchased from a Dealer at that time – after many efforts to remove air from the AHC system,

3. AHC and TEMS systems appeared to operate normally for five months until March 2022,

4. In March 2022, vehicle suddenly dropped to “LO” height setting while driving,

5. No leaks visible around the vehicle,

6. After returning home, used Techstream – see screenshots here.

7. Assume AHC Pump was working and an attempt was made to raise from “LO” to “N” to achieve the new Techstream measurements shown on the screenshot??? Please confirm. This is important!
Yes screenshot were taken before I bleed all 5 corners. I didn’t take any screenshot after I bleed all the fluid.

8. The AHC pressures on the screenshot are:
AHC Front: 2.1 Mpa;
AHC Rear: 5.0 MPa;
Height Control Accumulator: 0.0 Mpa.
All of these pressures are very low,

9. It is not known whether the AHC Pressure Sensor is working correctly and giving reliable outputs – this the large Sensor located on the AHC Pump Assembly on the metal block between the AHC Pump and its Motor,

10. The AHC Fluid temperature on the screenshot is: 118 degrees Fahrenheit -- this could be a little high and may suggest that the AHC Pump was operating or attempting to operate?

11. If AHC Pump was not working, then the AHC pressure readings on the screenshot are old numbers remembered by the Electronic Control Unit (ECU) and are meaningless,

I heard pump was very noisy and tried to run for 15-20 seconds.

12. If AHC Pump was working, and if the Pressure Sensor is reliable, then the AHC pressure readings indicate that the AHC Pump could not develop enough pressure and flow to raise the vehicle from “LO” to “N” height. The AHC Pump also could not refill the Height Control Accumulator -- because the vehicle did not complete the raise,

13. There was no AHC Fluid from bleeding the Height Control Accumulator. This means that the Height Control Accumulator had not previously been filled by the AHC Pump, so the Height Control Accumulator is empty – does not contain any AHC Fluid to bleed (but it may contain air),
There was fluid came out from height control accumulator. Once I drain all the fluid from 5 corners then was nothing coming out. I even tried to bleed while pump was running but line was empty.
14. Diagnostic Trouble Code (DTC) 1751 is shown on the screenshot. This means “AHC Pump & Motor Circuit” have not completed the raise from “LO” to “N” within the time limits,

15. Diagnostic Trouble Code (DTC) 1762 is shown on the screenshot. This means “Fluid Pressure Abnormality (Pump & Motor Does Not Supply Fluid)”,

16. Diagnostic Trouble Code (DTC) 1718 is not shown on the screenshot. This means that the signal from the “Fluid Pressure Sensor Circuit” to the ECU circuit should be reliable (but testing is a good idea anyway),

17. Back at the end of post #283 in this thread, see attachments detailing the defined conditions for each of DTC 1718, DTC 1751 and DTC 1762, along with the testing procedures and recommended action if No Good (NG),

18. Given these DTC’s, the AHC system is not operating, has dropped to “LO” height, and is not raising correctly. This is not surprising, because ….

19. ALL of DTC 1718, DTC 1751 and DTC 1762 have a similar ‘fail-safe mode’ as stated in the FSM: “If trouble occurs, the height control is prohibited after adjusting the vehicle to the standard height in case that the height is higher than the standard or to the lowest wheel of the 4 wheels in case that the height is lower than the standard”,

20. When these DTC’s show up, it means that the AHC system DOES NOT WORK – and once the vehicle is at “LO” height the AHC system is PROHIBITED by the ECU from raising automatically, until the problem causing the DTC is fixed,

21. How can this happen ‘suddenly’? Actually, it does not happen suddenly. Like most things on vehicles, there will have been a slow deterioration towards the conditions which cause these DTC’s (again, see attachments at the bottom of post #283 in this thread) -- until one day the defined conditions eventually are reached and the ECU puts the AHC system into ‘fail-safe mode’ for its own protection and for vehicle safety,

22. Attempted to bleed AHC system with vehicle at “LO” and noticed that AHC Pump was not taking in AHC Fluid from the AHC Tank – again, not really surprising, as above,

23. Zooming into picture at post #299 on this thread shows that a LOT of air was in AHC Fluid which came out of the system during recent efforts at bleeding,

24. The Techstream screenshots at post #299 on this thread are the same as the screenshots mentioned at paragraph 6 above. [By the way, it is best to stick with one thread for the same problem on the same vehicle – it causes confusion to readers trying to solve the problem when parts of your story are on different threads],

25. None of the recent screenshots for this vehicle show Front and Rear AHC pressures in the expected range per the Factory Service Manual (FSM),

26. None of the recent screenshots for this vehicle show Height Control Accumulator pressure anywhere near the expected value of around 10.5 Mpa,


Interpretation of the above symptoms:

There are several possibilities, mostly involving air or nitrogen gas in this system. This can have only three causes. It is suggested that these causes should be considered in the following order:

(A). Nitrogen gas escaping from behind worn-out membranes in very old ‘globes’. [If the ‘globes’ on this 2000 Lexus LX470 are more than 10 years old or have failed the attached HI/LO Test, then the ‘globes’ should be replaced],

AND/OR

(B). Air entering the system when the fluid level in the AHC Tank drops too low, or if air leaks around the seal between the AHC Tank and the AHC Pump. [When this happens, air goes to all parts of the AHC system – ‘globes’, shock absorbers, Height Control Accumulator – and then requires multiple bleeding efforts to remove the air. The suggestion at post #295 in this thread is a good way of clearing air out of the Height Control Accumulator],

AND/OR

(C). The inlet filter/strainer at the AHC Pump is blocked with debris from within the AHC system, or, from gelatinous or waxy substances in faulty AHC Fluid. [When this happens on the inlet side of a gear pump such as the AHC Pump, then the pump is starved of fluid. Either ‘cavitation’ takes place and the pump operates roughly and noisily and eventually could damage itself, OR, ‘aeration’ occurs when air is drawn in past the seals around the pump – in this case, around the small O-ring at the AHC Pump inlet, or around the large O-ring at the outer cover of the pump. This only happens for a short time until the ECU recognises a low pressure signal from the Pressure Sensor and the ‘fail-safe’ function stops the AHC Pump from destroying itself – and records the relevant DTC’s. How to check and clean internal fliter/strainers in the AHC Pump and how to deal with AHC Pump replacement and costs are described at post #280 and post #294 in this thread].


Conclusions:

There is no happiness in starting with AHC Pump replacement and then finding later that the real problem was air or gas still trapped in the AHC system – so first be very sure of effective bleeding procedures and be very confident that all air and/or nitrogen gas have been eliminated.

How can I bleed more when there’s nothing coming out of the bleed valves and nothing going down in the fluid reservoir.

When confident that air or nitrogen gas are not the problem, then it is time to investigate and replace the AHC Pump as described in earlier posts in this thread. After 22 years onboard a 2000 LX470, it is not too early and it is not expensive to replace the AHC Pump (if supplied by IMPEX or Partsouq). This will require a full re-bleeding of the system anyway.


Some further relevant information:

The “Active Test”:

The “Active Test” is used to check AHC operation.

It also can be used when it is desired to start an AHC Pump which has stopped and will not start automatically.

The main reason for such a stoppage is when air gets into the AHC Pump – such as during bleeding of the system, or if there is a poor seal between the AHC Tank and the AHC Pump, or at the O-rings within the AHC Pump assembly.

Air causes low pressure to be detected by the Pressure Sensor. The AHC Pump then stops for its own protection – it is not good for a gear pump to run without fluid for a long period.

The “Active Test” also can be used to start a pump when in ‘fail-safe’ mode while resolving the ‘fail-safe’ problem.

The “Active Test” can be done from the ‘Utility’ feature in Techstream, or, it can be done manually using the procedure below and at Section 5 of Page 6 of the “Pre-check” attachment.

The procedure should only be done for a short period of time -- about 10 seconds -- long enough to be sure that the pump is drawing fluid from the tank. This is called “priming” the pump:

1. With Ignition OFF, connect terminals Ts and E1 at DLC1 (this is the socket in the engine bay, usually over the RHS wheel arch with the word DIAGNOSTIC on the top cover. The terminal "map" is shown inside this cover. Instead of Special Service Tool (SST) 09843-18020 which is just a piece of bridging wire, find something simple -- I use an unbent paperclip for this test. Voltages here are low, about 4.5 volts, and will not cause a problem -- but be careful to connect the correct terminals,

2. Turn ON the engine.

3. Select “COMFORT” on the variable damping switch on the centre console,

4. Push the DOWN button on the Height Select switch within 5 seconds of engine start and hold it down for 5 seconds. There will many flashing lights in the instrument cluster (because the ECU functions are being by-passed). Ignore these -- they will revert to normal later, after the test, when the bridge (paperclip) is removed and the AHC ON/OFF switch is pressed down for a couple of seconds,

5. Use the combined settings to move front or rear up or down (listen for the operation of the AHC Pump and its motor),

6. When finished, switch OFF engine and switch OFF ignition, then remove the bridge (paperclip),

7. Re-start, push down and hold down the AHC ON/OFF for a couple of seconds to clear the test.


Height Control Accumulator problem before October 2002:

Vehicles manufactured before October 2002 are subject to possible failure of an O-ring inside the Height Control Accumulator. This O-ring cannot be replaced – see attached Technical Service Bulletin (TSB) CP-3006. [Aside: The TSB advises that the consequence is that this O-ring may break down and eventually find its way to the AHC Pump. At the AHC Pump this debris can clog one or both of the two small filter/strainers inside the AHC Pump. This is not the only possible cause of clogged AHC Pump filter/strainers. However caused, clogged filter/strainers at the AHC Pump will give rise to Diagnostic Trouble Codes (DTC’s) C1751 and C1762].

 

[IndroCruise]

I heard pump was very noisy and tried to run for 15-20 seconds.

How can I bleed more when there’s nothing coming out of the bleed valves and nothing going down in the fluid reservoir.

Hi @Muhammad Rais,

I was very sorry to read your ongoing frustrations.

When I think about the combination of symptoms on your vehicle – Items 1 to 26 in my earlier post #304 in this thread -- there are four possible basic causes in my mind.

Cause #1. Persistent air in the system -- despite many previous efforts to bleed air out of the system,

Cause #2. Nitrogen gas in the ‘globes’ passing through failed membranes into the AHC Fluid – membranes in the ‘globes’ do wear out and they are suspect when they give a poor result on the HI/LO test (attached to previous post) or when the ‘globes’ are more than 10 years old. So this can be a continuing source of bubbles in the AHC/TEMS system. The ‘globes’ won’t all fail at exactly the same time – but when one has failed it is a reasonable assumption that the rest are not far behind, so replace the whole set of four ‘globes’. Just now, you will not be able to do the HI/LO test because the vehicle will not raise to “HI” – but the ‘globes’ on this 2000 LX470 may be more that 10 years old?? More frustration!

Cause #3. Blockage in the internal filter/strainers inside the AHC Pump – unless there has been good basic hydraulic hygiene throughout the life of the vehicle with AHC Fluid changed at least every 6 years or 60,000 miles per Owner’s Manual (even better if changed every 3 years or 30,000 miles), then a build-up of sludge in the AHC system is inevitable over 22 years and a blockage of the filter/strainers eventually follows inside the AHC Pump. As the blockage at the inlet side of the pump slowly builds up, the pump is partially starved of fluid. It is a positive displacement gear pump of a good design which restricts internal bypass across the gears, and so the negative pressure the pump creates on its inlet side may draw (or ‘suck’) air past the internal seals and into the AHC Fluid. So more air arrives in the system!!

Cause #4. Faulty Height Control Sensors – there are three of these Sensors: Left Front, Right Front, Rear. They can be a problem in older vehicles, and like ‘globes’, they do eventually wear out. On vehicles operating in wet or salty conditions causing a lot of rust, Height Control Sensors do deteriorate more quickly and can cause some very erratic behaviour in the AHC/TEMS systems.

These are the causes I that I think best match the list of 26 symptoms and observations.

Of these, I think that faulty Height Control Sensors are the least likely. This vehicle lives in warm and dry Texas and the current symptoms do not strongly suggest Height Control Sensor problems.

There are other possibilities but these seem much less likely because they are not a good match with the descriptions in your posts – for example, problems with the electrical connectors, wiring harnesses, various fuses and relays, various sensors, various valves and actuators, problems with the Electronic Control Unit (ECU), etc.

That leaves the first three causes – and from the other side of the world, it is difficult to pick between them.

So what to do next?

If this were my vehicle (22 years old and 250,000 miles) and I wanted it to last, say at least another 5 years or at least another 60,000 miles with fully functional AHC/TEMS systems, this is what I would do:

1. Use “Active Test” and attempt to manually raise the vehicle from “LO” to approximately “N” height – maybe this answers your question: “How can I bleed more when there’s nothing coming out of the bleed valves and nothing going down in the fluid reservoir”?. Once raised, you can then bleed more.

2. Use the methods by @ramangain at post #295 or @blips at post #305 in this thread to attempt to re-fill the Height Control Accumulator – and if there is some success, repeat this several times before proceeding with normal bleeding,

3. If I judged that the AHC Pump was struggling and that the problem was more likely to be blockage in the AHC Pump, I would stop these attempts,

4. To test the idea of a blockage before tearing down the AHC Pump, I might disconnect the pipe from the AHC Pump outlet, then use “Active Test” to operate the AHC Pump to see whether there is a strong pressure and flow (catching the AHC Fluid in a container. (This will be a messy exercise, best done with the vehicle dropped to “LO” height or the bump stops, for lowest possible AHC pressure. Also, have plenty of rags around and be prepared for a clean-up. Use a good C-spanner to avoid rounding the pipe connector),

5. Alternatively, I might just get on with buying the relevant parts and get on with changing out the AHC Pump and also the ‘globes’ and possibly the Height Control Accumulator, using this Parts List below, and checking prices from:

• IMPEX -- IMPEX JAPAN — online new genuine spare parts shop - https://en.impex-jp.com/
• Partsouq -- PartSouq Auto Parts Around the World - https://partsouq.com/
• Preferred local supplier

Definite purchase:
48901-60010 – AHC Pump,
90311-10001 - oil seal between AHC Pump and Motor,
90301-70003 – large O-ring for AHC Pump,
90301-06012 – small O-ring for AHC Pump,
47255-60010 – grommet between AHC Tank and AHC Pump,
49189-60010 – replacement bleeder valves (5 required),
49177-60010 – replacement bleeder caps (5 required),
08886-01805 – AHC Fluid in 2.5 litre steel drums, at least two, probably three drums,

Probably, around USD200 for new OEM units in the above list, delivered from the overseas suppliers.

Definite purchase, unless ‘globes’ were replaced recently:
49141-60010 – Front ‘globes’, two required (often called ‘accumulators’ on parts websites),
49151-60010 – Rear ‘globes’, two required (often called ‘accumulators’ on parts websites),

Probably, around USD750 for four new OEM ‘globes’, delivered from the overseas suppliers.

Possible purchase, would first try to find a second-hand unit manufactured after October 2002:
49130-60010 – Height Control Accumulator,

Probably, around USD400 for new OEM unit, delivered from the overseas suppliers.

Long term purchase – later, not right now:
89405-60012 – Front Right Height Control Sensor
89406-60022 – Front Left Height Control Sensor
89407-60010 – Rear Height Control Sensor

Probably, around USD750 for three new OEM sensors, delivered from the overseas suppliers.

Whichever way you cut it, and unless you are planning on a some ultra heavy additions to the vehicle and/or some very tough rock-crawling, you will get a better and more pleasing result and probably at a better overall cost by renovating the AHC/TEMS system, instead of doing a make-over with a conventional suspension.

There will be ongoing suspension work over time -- for example, suspension bushings everywhere, front end mechanicals, rear end mechanicals but you are up for that anyway -- and the rest of the vehicle still needs to be maintained as well.

Yes – upkeep of the AHC/TEMS systems takes some effort and some love, and good workshop help is hard to find -- but already you are well advanced. Is it really that hard? Compare this system with the complexity of the brake system, steering system, auto transmission etc, etc, etc, on LC100/LX470 vehicles – not to mention all the systems on the various engines used

6. After replacing these parts, I would be very, very, very careful in trying to flush out as much as possible of the old AHC Fluid and debris remaining in the system. The worst outcome would be spending the money, doing the work, and then having remnant old fluid and debris in the system re-create the same problems (especially the problematic AHC Fluid which apparently was in the US market in 2021).

So I would adopt a very meticulous bleeding method, aiming at “best flush”, not necessarily "most economical use" of new AHC Fluid. Only imported 08886-01805 – AHC Fluid in 2.5 litre steel drums would be used. It is acknowledged that it is almost impossible to fully flush the AHC system, but I would be giving it my best shot.

This “Meticulous Method” is very pedantic -- but that is just me. It would be something like the following:

1. Vehicle is at “LO” or preferably on bump-stops,

2. Height Control Accumulator is empty,

3. Engine is “OFF”,

4. Half-fill AHC Tank with new AHC Fluid,

5. Start engine, raise vehicle to “N” while checking that Tank does not become empty (only half-fill tank because this ‘first fill’ fluid will be discarded later),

6. After raising vehicle, AHC Pump will fill Height Control Accumulator with new AHC Fluid,

7. Turn engine “OFF”, do ‘long bleed’ – leave bleeders open, rock vehicle, let all fluid come out -- from driver’s side AHC front and driver’s side AHC rear but NOT from Height Control Accumulator just yet,

8. Front and Rear of vehicle will drop as a result of bleeding and AHC Fluid will return to AHC tank,

9. Close bleeder valves (By the way, this project is the perfect opportunity to replace all bleeder valves 49189-60010, and also the important bleeder caps 49177-60010 -- very low cost items, just a few USD for five bleeders and five caps, from a local Dealer),

10. Remove ALL AHC Fluid from AHC Tank and discard – this fluid may contain debris in the system or bad fluid containing gel etc (previous fluid is suspicious quality, was purchased in 2021 in black 1 litre bottles),

11. Vehicle is at “LO” or preferably on bump-stops,

12. Engine is still “OFF”,

13. Height Control Accumulator still contains new AHC Fluid from Step 5 above,

14. Half-fill AHC Tank with new AHC Fluid,

15. Start engine, raise vehicle to “N” while checking that Tank does not become empty (only half-fill tank because this ‘second fill’ fluid also will be discarded later). THIS CAUSES HEIGHT CONTROL ACCUMULATOR TO SEND ITS NEW AHC FLUID INTO AHC SYSTEM TO RAISE VEHICLE, RAISE MAY BE FINISHED BY AHC PUMP USING NEW FLUID FROM TANK,

16. Turn engine “OFF”, do ‘long bleed’ – leave bleeders open, rock vehicle, let all fluid come out -- from passenger’s side AHC front and passenger’s side AHC rear but NOT from Height Control Accumulator just yet,

17. Front and Rear of vehicle will drop as a result of bleeding and AHC Fluid will return to AHC tank,

18. Close bleeder valves,

19. Remove ALL AHC Fluid from AHC Tank and discard – this fluid also may contain debris in the system or bad fluid containing gel etc (previous fluid is suspicious quality, was purchased in 2021 in black 1 litre bottles),

20. Vehicle is at “LO” or preferably on bump-stops,

21. Engine is still “OFF”,

22. Height Control Accumulator is EMPTY or close to empty – check by opening its bleeder, replace the bleeder and cap with new items, and close the bleeder,

23. Half-fill AHC Tank with new AHC Fluid,

24. Start engine, raise vehicle to “N” while checking that Tank does not become empty. AS BEFORE IN STEP 15, THIS CAUSES HEIGHT CONTROL ACCUMULATOR TO SEND ITS NEW AHC FLUID INTO AHC SYSTEM TO RAISE VEHICLE, RAISE MAY BE FINISHED BY AHC PUMP USING NEW FLUID FROM TANK,

Maybe these steps could be repeated now, using a lot more new AHC Fluid. If this were my vehicle, I would then do a final short bleed at all five bleeders just to clear any remaining air. Maybe that would be enough for now, probably I would run it for a few months before repeating the process.

Anyway, very best wishes for success with your vehicle!!

 

[Muhammad Rais]

Hi @Muhammad Rais,

I was very sorry to read your ongoing frustrations.

When I think about the combination of symptoms on your vehicle – Items 1 to 26 in my earlier post #304 in this thread -- there are four possible basic causes in my mind.

Cause #1. Persistent air in the system -- despite many previous efforts to bleed air out of the system,

Cause #2. Nitrogen gas in the ‘globes’ passing through failed membranes into the AHC Fluid – membranes in the ‘globes’ do wear out and they are suspect when they give a poor result on the HI/LO test (attached to previous post) or when the ‘globes’ are more than 10 years old. So this can be a continuing source of bubbles in the AHC/TEMS system. The ‘globes’ won’t all fail at exactly the same time – but when one has failed it is a reasonable assumption that the rest are not far behind, so replace the whole set of four ‘globes’. Just now, you will not be able to do the HI/LO test because the vehicle will not raise to “HI” – but the ‘globes’ on this 2000 LX470 may be more that 10 years old?? More frustration!

Cause #3. Blockage in the internal filter/strainers inside the AHC Pump – unless there has been good basic hydraulic hygiene throughout the life of the vehicle with AHC Fluid changed at least every 6 years or 60,000 miles per Owner’s Manual (even better if changed every 3 years or 30,000 miles), then a build-up of sludge in the AHC system is inevitable over 22 years and a blockage of the filter/strainers eventually follows inside the AHC Pump. As the blockage at the inlet side of the pump slowly builds up, the pump is partially starved of fluid. It is a positive displacement gear pump of a good design which restricts internal bypass across the gears, and so the negative pressure the pump creates on its inlet side may draw (or ‘suck’) air past the internal seals and into the AHC Fluid. So more air arrives in the system!!

Cause #4. Faulty Height Control Sensors – there are three of these Sensors: Left Front, Right Front, Rear. They can be a problem in older vehicles, and like ‘globes’, they do eventually wear out. On vehicles operating in wet or salty conditions causing a lot of rust, Height Control Sensors do deteriorate more quickly and can cause some very erratic behaviour in the AHC/TEMS systems.

These are the causes I that I think best match the list of 26 symptoms and observations.

Of these, I think that faulty Height Control Sensors are the least likely. This vehicle lives in warm and dry Texas and the current symptoms do not strongly suggest Height Control Sensor problems.

There are other possibilities but these seem much less likely because they are not a good match with the descriptions in your posts – for example, problems with the electrical connectors, wiring harnesses, various fuses and relays, various sensors, various valves and actuators, problems with the Electronic Control Unit (ECU), etc.

That leaves the first three causes – and from the other side of the world, it is difficult to pick between them.

So what to do next?

If this were my vehicle (22 years old and 250,000 miles) and I wanted it to last, say at least another 5 years or at least another 60,000 miles with fully functional AHC/TEMS systems, this is what I would do:

1. Use “Active Test” and attempt to manually raise the vehicle from “LO” to approximately “N” height – maybe this answers your question: “How can I bleed more when there’s nothing coming out of the bleed valves and nothing going down in the fluid reservoir”?. Once raised, you can then bleed more.

2. Use the methods by @ramangain at post #295 or @blips at post #305 in this thread to attempt to re-fill the Height Control Accumulator – and if there is some success, repeat this several times before proceeding with normal bleeding,

3. If I judged that the AHC Pump was struggling and that the problem was more likely to be blockage in the AHC Pump, I would stop these attempts,

4. To test the idea of a blockage before tearing down the AHC Pump, I might disconnect the pipe from the AHC Pump outlet, then use “Active Test” to operate the AHC Pump to see whether there is a strong pressure and flow (catching the AHC Fluid in a container. (This will be a messy exercise, best done with the vehicle dropped to “LO” height or the bump stops, for lowest possible AHC pressure. Also, have plenty of rags around and be prepared for a clean-up. Use a good C-spanner to avoid rounding the pipe connector),

5. Alternatively, I might just get on with buying the relevant parts and get on with changing out the AHC Pump and also the ‘globes’ and possibly the Height Control Accumulator, using this Parts List below, and checking prices from:

• IMPEX -- IMPEX JAPAN — online new genuine spare parts shop - https://en.impex-jp.com/
• Partsouq -- PartSouq Auto Parts Around the World - https://partsouq.com/
• Preferred local supplier

Definite purchase:
48901-60010 – AHC Pump,
90301-70003 – large O-ring for AHC Pump,
90301-06012 – small O-ring for AHC Pump,
47255-60010 – grommet between AHC Tank and AHC Pump,
49189-60010 – replacement bleeder valves (5 required),
49177-60010 – replacement bleeder caps (5 required),
08886-01805 – AHC Fluid in 2.5 litre steel drums, at least two, probably three drums,

Probably, around USD200 for new OEM units in the above list, delivered from the overseas suppliers.

Definite purchase, unless ‘globes’ were replaced recently:
49141-60010 – Front ‘globes’, two required (often called ‘accumulators’ on parts websites),
49151-60010 – Rear ‘globes’, two required (often called ‘accumulators’ on parts websites),

Probably, around USD750 for four new OEM ‘globes’, delivered from the overseas suppliers.

Possible purchase, would first try to find a second-hand unit manufactured after October 2002:
49130-60010 – Height Control Accumulator,

Probably, around USD400 for new OEM unit, delivered from the overseas suppliers.

Long term purchase – later, not right now:
89405-60012 – Front Right Height Control Sensor
89406-60022 – Front Left Height Control Sensor
89407-60010 – Rear Height Control Sensor

Probably, around USD750 for three new OEM sensors, delivered from the overseas suppliers.

Whichever way you cut it, and unless you are planning on a some ultra heavy additions to the vehicle and/or some very tough rock-crawling, you will get a better and more pleasing result and probably at a better overall cost by renovating the AHC/TEMS system, instead of doing a make-over with a conventional suspension.

There will be ongoing suspension work over time -- for example, suspension bushings everywhere, front end mechanicals, rear end mechanicals but you are up for that anyway -- and the rest of the vehicle still needs to be maintained as well.

Yes – upkeep of the AHC/TEMS systems takes some effort and some love, and good workshop help is hard to find -- but already you are well advanced. Is it really that hard? Compare this system with the complexity of the brake system, steering system, auto transmission etc, etc, etc, on LC100/LX470 vehicles – not to mention all the systems on the various engines used

6. After replacing these parts, I would be very, very, very careful in trying to flush out as much as possible of the old AHC Fluid and debris remaining in the system. The worst outcome would be spending the money, doing the work, and then having remnant old fluid and debris in the system re-create the same problems (especially the problematic AHC Fluid which apparently was in the US market in 2021).

So I would adopt a very meticulous bleeding method, aiming at “best flush”, not necessarily "most economical use" of new AHC Fluid. Only imported 08886-01805 – AHC Fluid in 2.5 litre steel drums would be used. It is acknowledged that it is almost impossible to fully flush the AHC system, but I would be giving it my best shot.

This “Meticulous Method” is very pedantic -- but that is just me. It would be something like the following:

1. Vehicle is at “LO” or preferably on bump-stops,

2. Height Control Accumulator is empty,

3. Engine is “OFF”,

4. Half-fill AHC Tank with new AHC Fluid,

5. Start engine, raise vehicle to “N” while checking that Tank does not become empty (only half-fill tank because this ‘first fill’ fluid will be discarded later),

6. After raising vehicle, AHC Pump will fill Height Control Accumulator with new AHC Fluid,

7. Turn engine “OFF”, do ‘long bleed’ – leave bleeders open, rock vehicle, let all fluid come out -- from driver’s side AHC front and driver’s side AHC rear but NOT from Height Control Accumulator just yet,

8. Front and Rear of vehicle will drop as a result of bleeding and AHC Fluid will return to AHC tank,

9. Close bleeder valves (By the way, this project is the perfect opportunity to replace all bleeder valves 49189-60010, and also the important bleeder caps 49177-60010 -- very low cost items, just a few USD for five bleeders and five caps, from a local Dealer),

10. Remove ALL AHC Fluid from AHC Tank and discard – this fluid may contain debris in the system or bad fluid containing gel etc (previous fluid is suspicious quality, was purchased in 2021 in black 1 litre bottles),

11. Vehicle is at “LO” or preferably on bump-stops,

12. Engine is still “OFF”,

13. Height Control Accumulator still contains new AHC Fluid from Step 5 above,

14. Half-fill AHC Tank with new AHC Fluid,

15. Start engine, raise vehicle to “N” while checking that Tank does not become empty (only half-fill tank because this ‘second fill’ fluid also will be discarded later). THIS CAUSES HEIGHT CONTROL ACCUMULATOR TO SEND ITS NEW AHC FLUID INTO AHC SYSTEM TO RAISE VEHICLE, RAISE MAY BE FINISHED BY AHC PUMP USING NEW FLUID FROM TANK,

16. Turn engine “OFF”, do ‘long bleed’ – leave bleeders open, rock vehicle, let all fluid come out -- from passenger’s side AHC front and passenger’s side AHC rear but NOT from Height Control Accumulator just yet,

17. Front and Rear of vehicle will drop as a result of bleeding and AHC Fluid will return to AHC tank,

18. Close bleeder valves,

19. Remove ALL AHC Fluid from AHC Tank and discard – this fluid also may contain debris in the system or bad fluid containing gel etc (previous fluid is suspicious quality, was purchased in 2021 in black 1 litre bottles),

20. Vehicle is at “LO” or preferably on bump-stops,

21. Engine is still “OFF”,

22. Height Control Accumulator is EMPTY or close to empty – check by opening its bleeder, replace the bleeder and cap with new items, and close the bleeder,

23. Half-fill AHC Tank with new AHC Fluid,

24. Start engine, raise vehicle to “N” while checking that Tank does not become empty. AS BEFORE IN STEP 15, THIS CAUSES HEIGHT CONTROL ACCUMULATOR TO SEND ITS NEW AHC FLUID INTO AHC SYSTEM TO RAISE VEHICLE, RAISE MAY BE FINISHED BY AHC PUMP USING NEW FLUID FROM TANK,

Maybe these steps could be repeated now, using a lot more new AHC Fluid. If this were my vehicle, I would then do a final short bleed at all five bleeders just to clear any remaining air. Maybe that would be enough for now, probably I would run it for a few months before repeating the process.

Anyway, very best wishes for success with your vehicle!!

Thank you so much for detailed information. I ordered from definitive parts list except globes. Will take them off and do a pencil test to verify how’s the globes. Ordered AHC pump and o rings from impex. Seems like it’s going to take long time to ship. I will keep you posted.
I wish any member here post a video on how to do the “active test”.
I am on the road and will be home on Sunday. Then I will try the active test.

 

[Muhammad Rais]

Hi @Muhammad Rais,

I was very sorry to read your ongoing frustrations.

When I think about the combination of symptoms on your vehicle – Items 1 to 26 in my earlier post #304 in this thread -- there are four possible basic causes in my mind.

Cause #1. Persistent air in the system -- despite many previous efforts to bleed air out of the system,

Cause #2. Nitrogen gas in the ‘globes’ passing through failed membranes into the AHC Fluid – membranes in the ‘globes’ do wear out and they are suspect when they give a poor result on the HI/LO test (attached to previous post) or when the ‘globes’ are more than 10 years old. So this can be a continuing source of bubbles in the AHC/TEMS system. The ‘globes’ won’t all fail at exactly the same time – but when one has failed it is a reasonable assumption that the rest are not far behind, so replace the whole set of four ‘globes’. Just now, you will not be able to do the HI/LO test because the vehicle will not raise to “HI” – but the ‘globes’ on this 2000 LX470 may be more that 10 years old?? More frustration!

Cause #3. Blockage in the internal filter/strainers inside the AHC Pump – unless there has been good basic hydraulic hygiene throughout the life of the vehicle with AHC Fluid changed at least every 6 years or 60,000 miles per Owner’s Manual (even better if changed every 3 years or 30,000 miles), then a build-up of sludge in the AHC system is inevitable over 22 years and a blockage of the filter/strainers eventually follows inside the AHC Pump. As the blockage at the inlet side of the pump slowly builds up, the pump is partially starved of fluid. It is a positive displacement gear pump of a good design which restricts internal bypass across the gears, and so the negative pressure the pump creates on its inlet side may draw (or ‘suck’) air past the internal seals and into the AHC Fluid. So more air arrives in the system!!

Cause #4. Faulty Height Control Sensors – there are three of these Sensors: Left Front, Right Front, Rear. They can be a problem in older vehicles, and like ‘globes’, they do eventually wear out. On vehicles operating in wet or salty conditions causing a lot of rust, Height Control Sensors do deteriorate more quickly and can cause some very erratic behaviour in the AHC/TEMS systems.

These are the causes I that I think best match the list of 26 symptoms and observations.

Of these, I think that faulty Height Control Sensors are the least likely. This vehicle lives in warm and dry Texas and the current symptoms do not strongly suggest Height Control Sensor problems.

There are other possibilities but these seem much less likely because they are not a good match with the descriptions in your posts – for example, problems with the electrical connectors, wiring harnesses, various fuses and relays, various sensors, various valves and actuators, problems with the Electronic Control Unit (ECU), etc.

That leaves the first three causes – and from the other side of the world, it is difficult to pick between them.

So what to do next?

If this were my vehicle (22 years old and 250,000 miles) and I wanted it to last, say at least another 5 years or at least another 60,000 miles with fully functional AHC/TEMS systems, this is what I would do:

1. Use “Active Test” and attempt to manually raise the vehicle from “LO” to approximately “N” height – maybe this answers your question: “How can I bleed more when there’s nothing coming out of the bleed valves and nothing going down in the fluid reservoir”?. Once raised, you can then bleed more.

2. Use the methods by @ramangain at post #295 or @blips at post #305 in this thread to attempt to re-fill the Height Control Accumulator – and if there is some success, repeat this several times before proceeding with normal bleeding,

3. If I judged that the AHC Pump was struggling and that the problem was more likely to be blockage in the AHC Pump, I would stop these attempts,

4. To test the idea of a blockage before tearing down the AHC Pump, I might disconnect the pipe from the AHC Pump outlet, then use “Active Test” to operate the AHC Pump to see whether there is a strong pressure and flow (catching the AHC Fluid in a container. (This will be a messy exercise, best done with the vehicle dropped to “LO” height or the bump stops, for lowest possible AHC pressure. Also, have plenty of rags around and be prepared for a clean-up. Use a good C-spanner to avoid rounding the pipe connector),

5. Alternatively, I might just get on with buying the relevant parts and get on with changing out the AHC Pump and also the ‘globes’ and possibly the Height Control Accumulator, using this Parts List below, and checking prices from:

• IMPEX -- IMPEX JAPAN — online new genuine spare parts shop - https://en.impex-jp.com/
• Partsouq -- PartSouq Auto Parts Around the World - https://partsouq.com/
• Preferred local supplier

Definite purchase:
48901-60010 – AHC Pump,
90301-70003 – large O-ring for AHC Pump,
90301-06012 – small O-ring for AHC Pump,
47255-60010 – grommet between AHC Tank and AHC Pump,
49189-60010 – replacement bleeder valves (5 required),
49177-60010 – replacement bleeder caps (5 required),
08886-01805 – AHC Fluid in 2.5 litre steel drums, at least two, probably three drums,

Probably, around USD200 for new OEM units in the above list, delivered from the overseas suppliers.

Definite purchase, unless ‘globes’ were replaced recently:
49141-60010 – Front ‘globes’, two required (often called ‘accumulators’ on parts websites),
49151-60010 – Rear ‘globes’, two required (often called ‘accumulators’ on parts websites),

Probably, around USD750 for four new OEM ‘globes’, delivered from the overseas suppliers.

Possible purchase, would first try to find a second-hand unit manufactured after October 2002:
49130-60010 – Height Control Accumulator,

Probably, around USD400 for new OEM unit, delivered from the overseas suppliers.

Long term purchase – later, not right now:
89405-60012 – Front Right Height Control Sensor
89406-60022 – Front Left Height Control Sensor
89407-60010 – Rear Height Control Sensor

Probably, around USD750 for three new OEM sensors, delivered from the overseas suppliers.

Whichever way you cut it, and unless you are planning on a some ultra heavy additions to the vehicle and/or some very tough rock-crawling, you will get a better and more pleasing result and probably at a better overall cost by renovating the AHC/TEMS system, instead of doing a make-over with a conventional suspension.

There will be ongoing suspension work over time -- for example, suspension bushings everywhere, front end mechanicals, rear end mechanicals but you are up for that anyway -- and the rest of the vehicle still needs to be maintained as well.

Yes – upkeep of the AHC/TEMS systems takes some effort and some love, and good workshop help is hard to find -- but already you are well advanced. Is it really that hard? Compare this system with the complexity of the brake system, steering system, auto transmission etc, etc, etc, on LC100/LX470 vehicles – not to mention all the systems on the various engines used

6. After replacing these parts, I would be very, very, very careful in trying to flush out as much as possible of the old AHC Fluid and debris remaining in the system. The worst outcome would be spending the money, doing the work, and then having remnant old fluid and debris in the system re-create the same problems (especially the problematic AHC Fluid which apparently was in the US market in 2021).

So I would adopt a very meticulous bleeding method, aiming at “best flush”, not necessarily "most economical use" of new AHC Fluid. Only imported 08886-01805 – AHC Fluid in 2.5 litre steel drums would be used. It is acknowledged that it is almost impossible to fully flush the AHC system, but I would be giving it my best shot.

This “Meticulous Method” is very pedantic -- but that is just me. It would be something like the following:

1. Vehicle is at “LO” or preferably on bump-stops,

2. Height Control Accumulator is empty,

3. Engine is “OFF”,

4. Half-fill AHC Tank with new AHC Fluid,

5. Start engine, raise vehicle to “N” while checking that Tank does not become empty (only half-fill tank because this ‘first fill’ fluid will be discarded later),

6. After raising vehicle, AHC Pump will fill Height Control Accumulator with new AHC Fluid,

7. Turn engine “OFF”, do ‘long bleed’ – leave bleeders open, rock vehicle, let all fluid come out -- from driver’s side AHC front and driver’s side AHC rear but NOT from Height Control Accumulator just yet,

8. Front and Rear of vehicle will drop as a result of bleeding and AHC Fluid will return to AHC tank,

9. Close bleeder valves (By the way, this project is the perfect opportunity to replace all bleeder valves 49189-60010, and also the important bleeder caps 49177-60010 -- very low cost items, just a few USD for five bleeders and five caps, from a local Dealer),

10. Remove ALL AHC Fluid from AHC Tank and discard – this fluid may contain debris in the system or bad fluid containing gel etc (previous fluid is suspicious quality, was purchased in 2021 in black 1 litre bottles),

11. Vehicle is at “LO” or preferably on bump-stops,

12. Engine is still “OFF”,

13. Height Control Accumulator still contains new AHC Fluid from Step 5 above,

14. Half-fill AHC Tank with new AHC Fluid,

15. Start engine, raise vehicle to “N” while checking that Tank does not become empty (only half-fill tank because this ‘second fill’ fluid also will be discarded later). THIS CAUSES HEIGHT CONTROL ACCUMULATOR TO SEND ITS NEW AHC FLUID INTO AHC SYSTEM TO RAISE VEHICLE, RAISE MAY BE FINISHED BY AHC PUMP USING NEW FLUID FROM TANK,

16. Turn engine “OFF”, do ‘long bleed’ – leave bleeders open, rock vehicle, let all fluid come out -- from passenger’s side AHC front and passenger’s side AHC rear but NOT from Height Control Accumulator just yet,

17. Front and Rear of vehicle will drop as a result of bleeding and AHC Fluid will return to AHC tank,

18. Close bleeder valves,

19. Remove ALL AHC Fluid from AHC Tank and discard – this fluid also may contain debris in the system or bad fluid containing gel etc (previous fluid is suspicious quality, was purchased in 2021 in black 1 litre bottles),

20. Vehicle is at “LO” or preferably on bump-stops,

21. Engine is still “OFF”,

22. Height Control Accumulator is EMPTY or close to empty – check by opening its bleeder, replace the bleeder and cap with new items, and close the bleeder,

23. Half-fill AHC Tank with new AHC Fluid,

24. Start engine, raise vehicle to “N” while checking that Tank does not become empty. AS BEFORE IN STEP 15, THIS CAUSES HEIGHT CONTROL ACCUMULATOR TO SEND ITS NEW AHC FLUID INTO AHC SYSTEM TO RAISE VEHICLE, RAISE MAY BE FINISHED BY AHC PUMP USING NEW FLUID FROM TANK,

Maybe these steps could be repeated now, using a lot more new AHC Fluid. If this were my vehicle, I would then do a final short bleed at all five bleeders just to clear any remaining air. Maybe that would be enough for now, probably I would run it for a few months before repeating the process.

Anyway, very best wishes for success with your vehicle!!

Hi all, great news. My LX AHC is working flawlessly. After almost 3 months made time to swap the internal pump received from impex. Also changed the seals. Used metal can AHC fluid. Pump was not clogged or anything. It was very clean inside. Old pump pictures attached. Old pump used to make noises and very hot. New one is so quiet and doesn’t get hot anywhere close to the old one. Special thanks to Indrocruise for his patience to answer my questions. Also everyone else who helped me to fix AHC. I was at a point to get rid off AHC and go with conventional setup. I am very satisfied with the outcome. I was thinking to change the globes but I will drive it now like this and maybe later will think of it. I will get the screenshot this week and post it here.

 

[suprasvobodea]

To fix the lack of fluid coming out of accumulator .....

Buy 4+ bottles of new fluid. You'll recycle it during the steps below.

1. Crack open the accumulator valve to drain. Attach a hose to it and settle hose end to fill a large container.
2. Start the truck. Let the fluid come out until the resevoir is getting low.
3. Close the valve, stop the truck.
4. Recycle the drained fluid into the resevoir.
5. Start the truck, work the AHC system up and down a few times.
6. Repeat as necessary to chase the air out of the accumulator.

It took several cycles of this process to purge all of the air from my accumulator. Good luck!

Ramangam

I need some help with air in my AHC pump after changing out the "shocks" and replacing the accumulator (after shearing the bleed fitting!) I will provide the specifics of my situation, with as much detail as I can, so you or Ramangain or whoever sees this, maybe can help me solve this very puzzling situation I have now, after replacing the bushings in both rear and front shocks (hydraulic actuators -really).and the Accumulator!

Here are the specifics and what I have checked or done so far:

I have a 2002 Lx470 with 230K miles. It's a TEXAS truck so thankfully, it's not rusted out and destroyed like where I grew up in Wisconsin.
I replaced all 4 globes 4-5 months ago, as I had just 7 graduations and an F-250-like ride! ( now I have 12 graduations)
I had broken off the bleed valve on the accumulator, ( BTW>> This is THE WORST replacement project on the entire AHC system! I will write up a separate, photo-supplied, detailed plan about removing and replacing the ACCUMULATOR and its supply line from the reservoir) to share with everyone after I get this AHC pump issue resolved.

I finally got a TECHSTREAM Ver. 18 installed and WORKING properly on my laptop after several months and countless research for a version that I could download and ........... get to work!
Ok, so after installing a new accumulator I got from IMPEX for just $220 I think,( more than 50% LESS than anything available here in the US) and refilling all 4 shocks with new fluid and re-install them with new bushings for the sway bar links, and sway bar strap bushing I was ready to refill and test my new AHC system!

After installing a new Accumulator, AND the new line that runs to the accumulator from the fluid reservoir across the underside of the truck, I filled the reservoir 3/4 full of fresh fluid ( from the 2.5L metal can)- I never used any of the fluid from the black, plastic bottles that some dealers used to sell it in. ) I started it up and pushed the UP button. It took about 20-30 seconds to get going but I was not outside watching the tank and it got pretty low. I couldn't see through the cloudy, opaque reservoir but I quickly added 1/2 can more fluid. It may have gone too low, but regardless, there is air in the system.
When I started bleeding globes, it was full of bubbles. after the first bleed, I pushed the UP button ( it was down to stops) and it slowly started rising, then I heard a new sound, like groaning ... and it went away after 10 seconds, back to normal quiet. As I proceeded, it gradually stopped pumping and the OFF light started rapidly flashing. I checked the codes and I had 2.

1736- Accumulator solenoid, Accumulator solenoid circuit ( this went away after I cleared the codes and probably was the result of a new accumulator connected back into the system)
1762- AHC pump, Fuel pressure sensor, AHC motor relay

View attachment 3547205

Since I disconnected the Accumulator, I figured that would trigger code 1736. But the dreaded "1762" code..... that is my nightmare! . I tried to run the "active test" that's in the Lexus repair manual on the page (DI-236), by jumping the DLC1 located on the pass side engine bay - right beside the AHC pump !) with Ts-E1 and pressing DOWN within 5 seconds after starting. There is also a manual method ( without tech stream) by doing the same jumper on the DLC1 Page ( DI 275). However,... I never got the flashing OFF light on the instrument panel to stop its 0.25-second flashing so the UP button push would manually start the pump. That's what is puzzling me. After following the TRSM, that would override the failsafe system.
Also, per the Lexus TSRM on page Di-274, the next step is to apply 12V directly to the pump, to make sure it's still running. I did that and it hummed, I even cracked the outlet fitting at the base of the pump to clear any air that might be in the pump to manually prime it ( an old lesson l learned from working in our apple orchid in Wis for the tractor mounted High-pressure sprayer for the trees).
So, I thought;
1. If there was air trapped in the pump, it would be expelled into the loosened outlet fitting as it spurted fluid while spinning
2. Applying 12v to the pump ensured it was still working.

BTW:- Everything was working perfectly before I opened it up to install a new Accumulator due to a sheared-off bleed valve. ( Use a MAPP or propane torch & lots of soaking with PB Blaster, BEFORE trying to loosen any bleeder screw !!!!! I would have saved 200 + hours and $$$ if i would have done this!

BLEEDING :
In a previous post, I read RAMANGAIN has a similar problem with the Accumulator full of air, so I tried his solution, bleeding the accumulator repetitively, but my problem is back to the FIRST issue..... I CANNOT OVERRIDE THE FAILSAFE SYSTEM TO MAKE THE PUMP RUN!
I even tried to apply 12 directly for 1 minute, and I heard it running, but then it started to make a loud noise ( like cavitation) so I stopped. It was sporadic,.. so I don't know what to think ...
Next, I checked all 4 globes, the front driver side had high pressure and pushed off the bleed hose and made a big mess. Then I tried the pass front, it was dead, then the pass rear, .. same thing, empty. Then driverside rear.... no pressure. Finally, the accumulator it was empty.

In summary, when I first started, I could get the system to function and move from L > N. I never got it to H. After several attempts to initiate the "active test" and let it sit overnight,.. now it simply WILL NOT PUMP !!!

So, my question is ..
What do I check or do next?? What did I miss? I probably got air in the system when the reservoir was almost empty. Ok, that would happen if I replaced the pump - right ??? SO.... what am I missing....? How do I override the "failsafe" control of the computer and get the pump to build pressure again? I feel frustrated that after all this work on replacing, fixing, and repairing broken parts,... I should be rewarded with a working, operative AHC!

 

[suprasvobodea]

It is very important to be sure that bleeding is good and that the problem is not caused by air somehow entering the system and remaining there from the previous effort at bleeding some time ago, just before these problems started (your Post #269 and Post #276). As described by @aharlan001 earlier in this very long thread and by others elsewhere, removing reluctant air can take many bleeding efforts. This means repeating the @PADDO process but using ALL five bleeders one by one and allowing the engine and the AHC Pump to run to push fluid through, but being very careful not to allow the fluid level in the tank to drop to empty and allow even more air to enter the system.

When air becomes "stuck" in the Height Control Accumulator, or in the Shock Absorbers, or in the long pipes from the pump to 'globes' and shock absorbers, it is difficult to shift. In such cases, bleeding from each of the four bleeders near each 'globe' is important, not just from one side. This is because when there are difficulties, the location of the air cannot be assumed and the air must be given every opportunity to escape.

It is also important to ensure that the Height Control Accumulator is filled and that bleeding takes place when it is full. The Height Control Accumulator only refills after a raise from "LO" to "N" or "N" to "HI". This can be difficult and may take multiple efforts of trying to get the vehicle to lower then raise.

Bleeding is not complete until there is good flow with no bubbles appearing from all four bleeders near the 'globes' and from the Height Control Accumulator, with no froth in the container used to catch the fluid. If nothing or not much comes out of the Height Control Accumulator (should see at least 300 millilitres or a good cupful), then this is unsatisfactory. It means that the Accumulator has not been filled with fluid -- it needs to fill and then bleeding has to be done.

When and if convinced that bleeding is good and the problem is not a due to air in the system, then it is time to consider problems at the AHC Pump and whether or not the AHC system is building sufficient pressure. The low Height Control Accumulator pressure of 8.9Mpa (should be around 10.5Mpa) may be indicating a problem with pump pressure -- but as already mentioned, this Height Control Accumulator pressure also can be caused by air in the Accumulator.

If proceeding down the path of examining the AHC Pump, suggest first test the Pressure Sensor as a prelimary step even though DTC C1718 is not reported.

Then review the attachments for

C1751 AHC Pump & Motor Circuit
C1762 Fluid Pressure Abnormality

In each case, decide whether the symptoms you observe on the vehicle correspond with the description under the heading "Fail safe Function" listed just below the table on first page on both of the relevant attachments.

If the conclusion is suspicion about a partial blockage in the AHC Pump -- such as at the small screens/strainers inside the pump impeding pressure and flow -- then it becomes necessary to depressurise the AHC system and remove and inspect the AHC Pump.

Suggest review the information at Post #273 by @Dref and also the information and especially the links within my Post #280 and also the information and link at Post #282 by @ktmracer01 -- all in this thread. This information describes how to remove the AHC Pump, and also provides comments about inspection and cleaning of the pump or its possible replacement.

See also similar information at Post #10 at this thread:

AHC pump removal with pics

This is an attempt to explain how I removed and replaced the AHC pump with a few pictures to help. Tools needed are... --10 mm deep socket (for bolt under reservoir) --10mm wrench --10mm crowfoot or small 10mm ratchet would be gold for other bolt holding reservoir --fluid extractor hose and...

forum.ih8mud.com

Hope this helps.

Hello IndroCrusie

I need some help with air in my pump after changing out the "shocks) and replacing the accumulator after shearing the bleed fitting! I will provide the specifics of my situation, with as much detail as I can, so you or Ramangain or whoever sees this, maybe can help me solve this very puzzling situation I have now, after replacing the bushings in both rear and front shocks (hydraulic actuators -really).and the Accumulator!

Here are my specifics and what I have checked or done so far:

I have a 2002 Lx470 with 230K miles. It's a TEXAS truck so thankfully, it's not rusted out and destroyed like where I grew up in Wisconsin.
I replaced all 4 globes 4-5 months ago, as I had 7 graduations and an F-250-like ride! ( now I have 12 graduations)
I had broken off the bleed valve on the accumulator, ( this is THE WORST replacement project on the entire AHC system! I will write up a separate, photo-supplied, detailed plan to share with everyone after I get this AHC pump issue resolved.

I finally got a TECHSTREAM Ver. 18 installed and WORKING properly on my laptop after several months and countless research for a version that I could download and ........... get to work!
Ok, so after installing a new accumulator I got from IMPEX for just $220 I think,( more than 50% LESS than anything available here in the US) and refilling all 4 shocks with new fluid and re-install them with new bushings for the sway bar links, and sway bar strap bushing I was ready to refill and test my new AHC system!

After installing a new Accumulator, AND the new line that runs to the accumulator from the fluid reservoir across the underside of the truck, I filled the reservoir 3/4 full of fresh fluid ( from the 2.5L metal can)- I never used any of the fluid from the black, plastic bottles that some dealers used to sell it in. ) I started it up and pushed the UP button. It took about 20-30 seconds to get going but I was not outside watching the tank and it got pretty low. I couldn't see through the cloudy, opaque reservoir but I quickly added 1/2 can more fluid. It may have gone too low, but regardless, there is air in the system.
When I started bleeding globes, it was full of bubbles. after the first bleed, I pushed the UP button ( it was down to stops) and it slowly started rising, then I heard a new sound, like groaning ... and it went away after 10 seconds, back to normal quiet. As I proceeded, it gradually stopped pumping and the OFF light started rapidly flashing. I checked the codes and I had 2.

1736- Accumulator solenoid, Accumulator solenoid circuit ( this went away after I cleared the codes and probably was the result of a new accumulator connected back into the system)
1762- AHC pump, Fuel pressure sensor, AHC motor relay

Since I disconnected the Accumulator, I figured that would trigger code 1736. But the dreaded "1762" code..... that is my nightmare! . I tried to run the "active test" that's in the Lexus repair manual on the page (DI-236), by jumping the DLC1 located on the pass side engine bay - right beside the AHC pump !) with Ts-E1 and pressing DOWN within 5 seconds after starting. There is also a manual method ( without tech stream) by doing the same jumper on the DLC1 Page ( DI 275). However,... I never got the flashing OFF light on the instrument panel to stop its 0.25-second flashing so the UP button push would manually start the pump. That's what is puzzling me. After following the TRSM, that would override the failsafe system.
Also, per the Lexus TSRM on page Di-274, the next step is to apply 12V directly to the pump, to make sure it's still running. I did that and it hummed, I even cracked the outlet fitting at the base of the pump to clear any air that might be in the pump to manually prime it ( an old lesson l learned from working in our apple orchid in Wis for the tractor mounted High-pressure sprayer for the trees).
So, I thought;
1. If there was air trapped in the pump, it would be expelled into the loosened outlet fitting as it spurted fluid while spinning
2. Applying 12v to the pump ensured it was still working.

BTW:- Everything was working perfectly before I opened it up to install a new Accumulator due to a sheared-off bleed valve. ( Use a MAPP or propane torch & lots of soaking with PB Blaster, BEFORE trying to loosen any bleeder screw !!!!! I would have saved 200 + hours and $$$ if i would have done this!

BLEEDING :
In a previous post, I read RAMANGAIN has a similar problem with the Accumulator full of air, so I tried his solution, bleeding the accumulator repetitively, but my problem is back to the FIRST issue..... I CANNOT OVERRIDE THE FAILSAFE SYSTEM TO MAKE THE PUMP RUN!
I even tried to apply 12 directly for 1 minute, and I heard it running, but then it started to make a loud noise ( like cavitation) so I stopped. It was sporadic,.. so I don't know what to think ...
Next, I checked all 4 globes, the front driver side had high pressure and pushed off the bleed hose and made a big mess. Then I tried the pass front, it was dead, then the pass rear, .. same thing, empty. Then driverside rear.... no pressure. Finally, the accumulator it was empty.

In summary, when I first started, I could get the system to function and move from L > N. I never got it to H. After several attempts to initiate the "active test" and let it sit overnight,.. now it simply WILL NOT PUMP !!!

So, my question is ..
What do I check or do next?? What did I miss? I probably got air in the system when the reservoir was almost empty. Ok, that would happen if I replaced the pump - right ??? SO.... what am I missing....? How do I override the "failsafe" control of the computer and get the pump to build pressure again? I feel frustrated that after all this work on replacing, fixing, and repairing broken parts,... I should be rewarded with a working, operative AHC!

 

[IndroCruise]

Hello IndroCrusie

I need some help with air in my pump after changing out the "shocks) and replacing the accumulator after shearing the bleed fitting! I will provide the specifics of my situation, with as much detail as I can, so you or Ramangain or whoever sees this, maybe can help me solve this very puzzling situation I have now, after replacing the bushings in both rear and front shocks (hydraulic actuators -really).and the Accumulator!

Here are my specifics and what I have checked or done so far:

I have a 2002 Lx470 with 230K miles. It's a TEXAS truck so thankfully, it's not rusted out and destroyed like where I grew up in Wisconsin.
I replaced all 4 globes 4-5 months ago, as I had 7 graduations and an F-250-like ride! ( now I have 12 graduations)
I had broken off the bleed valve on the accumulator, ( this is THE WORST replacement project on the entire AHC system! I will write up a separate, photo-supplied, detailed plan to share with everyone after I get this AHC pump issue resolved.

I finally got a TECHSTREAM Ver. 18 installed and WORKING properly on my laptop after several months and countless research for a version that I could download and ........... get to work!
Ok, so after installing a new accumulator I got from IMPEX for just $220 I think,( more than 50% LESS than anything available here in the US) and refilling all 4 shocks with new fluid and re-install them with new bushings for the sway bar links, and sway bar strap bushing I was ready to refill and test my new AHC system!

After installing a new Accumulator, AND the new line that runs to the accumulator from the fluid reservoir across the underside of the truck, I filled the reservoir 3/4 full of fresh fluid ( from the 2.5L metal can)- I never used any of the fluid from the black, plastic bottles that some dealers used to sell it in. ) I started it up and pushed the UP button. It took about 20-30 seconds to get going but I was not outside watching the tank and it got pretty low. I couldn't see through the cloudy, opaque reservoir but I quickly added 1/2 can more fluid. It may have gone too low, but regardless, there is air in the system.
When I started bleeding globes, it was full of bubbles. after the first bleed, I pushed the UP button ( it was down to stops) and it slowly started rising, then I heard a new sound, like groaning ... and it went away after 10 seconds, back to normal quiet. As I proceeded, it gradually stopped pumping and the OFF light started rapidly flashing. I checked the codes and I had 2.

1736- Accumulator solenoid, Accumulator solenoid circuit ( this went away after I cleared the codes and probably was the result of a new accumulator connected back into the system)
1762- AHC pump, Fuel pressure sensor, AHC motor relay

View attachment 3547205

Since I disconnected the Accumulator, I figured that would trigger code 1736. But the dreaded "1762" code..... that is my nightmare! . I tried to run the "active test" that's in the Lexus repair manual on the page (DI-236), by jumping the DLC1 located on the pass side engine bay - right beside the AHC pump !) with Ts-E1 and pressing DOWN within 5 seconds after starting. There is also a manual method ( without tech stream) by doing the same jumper on the DLC1 Page ( DI 275). However,... I never got the flashing OFF light on the instrument panel to stop its 0.25-second flashing so the UP button push would manually start the pump. That's what is puzzling me. After following the TRSM, that would override the failsafe system.
Also, per the Lexus TSRM on page Di-274, the next step is to apply 12V directly to the pump, to make sure it's still running. I did that and it hummed, I even cracked the outlet fitting at the base of the pump to clear any air that might be in the pump to manually prime it ( an old lesson l learned from working in our apple orchid in Wis for the tractor mounted High-pressure sprayer for the trees).
So, I thought;
1. If there was air trapped in the pump, it would be expelled into the loosened outlet fitting as it spurted fluid while spinning
2. Applying 12v to the pump ensured it was still working.

BTW:- Everything was working perfectly before I opened it up to install a new Accumulator due to a sheared-off bleed valve. ( Use a MAPP or propane torch & lots of soaking with PB Blaster, BEFORE trying to loosen any bleeder screw !!!!! I would have saved 200 + hours and $$$ if i would have done this!

BLEEDING :
In a previous post, I read RAMANGAIN has a similar problem with the Accumulator full of air, so I tried his solution, bleeding the accumulator repetitively, but my problem is back to the FIRST issue..... I CANNOT OVERRIDE THE FAILSAFE SYSTEM TO MAKE THE PUMP RUN!
I even tried to apply 12 directly for 1 minute, and I heard it running, but then it started to make a loud noise ( like cavitation) so I stopped. It was sporadic,.. so I don't know what to think ...
Next, I checked all 4 globes, the front driver side had high pressure and pushed off the bleed hose and made a big mess. Then I tried the pass front, it was dead, then the pass rear, .. same thing, empty. Then driverside rear.... no pressure. Finally, the accumulator it was empty.

In summary, when I first started, I could get the system to function and move from L > N. I never got it to H. After several attempts to initiate the "active test" and let it sit overnight,.. now it simply WILL NOT PUMP !!!

So, my question is ..
What do I check or do next?? What did I miss? I probably got air in the system when the reservoir was almost empty. Ok, that would happen if I replaced the pump - right ??? SO.... what am I missing....? How do I override the "failsafe" control of the computer and get the pump to build pressure again? I feel frustrated that after all this work on replacing, fixing, and repairing broken parts,... I should be rewarded with a working, operative AHC!

View attachment 3547207

Frustration+++ from @suprasvobodea and posts in two threads looking for advice. You already have learned a lot about the AHC/TEMS systems on LC100/LX470 vehicles. Here a few thoughts which may help you go further ….

Summarising the situation, as I understand it:

• 2002 LX470 at 230k miles, Texas domicile, not rusted out,
• new ‘globes’ Front and Rear, 4-5 months ago, then 12 graduations at AHC Tank on HI/LO test,
• existing ‘shock absorbers’ still serviceable, removed and replaced after fitting new bushings,
• new Height Control Accumulator installed (bleeder broken on original Height Control Accumulator),
• “new line that runs to the (Height Control?) accumulator from the fluid reservoir across the underside of the truck”. There is no such single direct line so what does this mean? The line from the AHC Pump to the Pump Attenuator? Or the Pump Attenuator itself? Or the line from the Pump Attenuator to the Control Valve Assembly? Or the line from the Control Valve Assembly to the Height Control Accumulator? Anyway, it seems that a new tube has been fitted in one of these places,
• new AHC Fluid used from steel can Part Number 08886-01805, not from problematic plastic bottles Part Number 8886-81221,
• Height Control Operation Test (“Active Test”) is not working using Techstream nor with the manual method using connections at DLC1. [Note: This test will not work if there is a fault/DTC in the AHC system, such as C1762 or C1751 etc],
• C1736 appeared initially but was cleared later,
• Note: Fail safe function for C1736: “If trouble occurs in the Control Valve Assembly circuit (BTW this includes the circuit to the Solenoid Valve at the front of the Height Control Accumulator), then the ECU prohibits the height control function and fixes the damping force at the Sports mode”. Symptoms to look for: No AHC function; VERY rough ride because TEMS damping function is FIXED at Sports mode. Could mean problem connectors, problem harness wiring, or problem components],
• Per FSM, C1736 is caused by incorrect “B” voltages as read by ECU – could be caused by faulty solenoid (new, seems unlikely, but maybe check the solenoid for internal continuity per FSM anyway), or, check loose or damaged connector (possible, so inspect, test), or, check for damaged wiring (possible, so inspect, test -- this cause is reported increasingly often as these LC100/LX470 vehicles age ), or, faulty ECU (possible but very unlikely in the absence of other symptoms elsewhere in the AHC/TEMS systems),
• Per FSM, C1762 is caused by low delivery pressure from the AHC Pump. It is a very quick-acting response -- this positive displacement gear pump stops after 0.6 seconds under the FSM-specified DTC fault conditions and then DTC C1762 is set, needs to be rectified and cleared. The design purpose is to protect the pump from excessive cavitation and internal destructive wear and damage if the pump cannot draw sufficient fluid from the AHC Tank, usually due to a partially blocked strainer on the inlet side within the pump. Blockages are increasingly likely as these LC100/LX470 vehicles age and especially if AHC Fluid has not been replaced at least as often as specified in Owners Manual, every 60,000 miles – preferably twice as often. If not done, sludge or gel accumulates in the system – especially between the pump sub-assembly Part Number 48901-60010 and the outer case with the big “+” sign on it (faces the firewall on LHD vehicles),

A similar outcome occurs if

• the AHC Pump has an ‘air-lock’, or,
• if there is entrained air or dissolved air in the AHC Fluid and the pump ‘sucks’ air (and/or tries to compress air in the system rather than pumping fluid) – in the AHC Pump this would be called ‘aeration’ rather than ‘cavitation’ but the effect on pump performance is much the same, or,
• if the internal components of the AHC Pump sub-assembly are worn or damaged and there is too much fluid bypassing above or below the gear set rather than through the gear teeth which are responsible for the pumping effort -- then there will be low pump delivery. [Aside: this is a positive displacement gear pump -- it delivers volume flow, pressure only arises if there is resistance to fluid flow], or,
• if there is a fault in the AHC Pump Motor (unlikely if the pump runs when tested on direct 12 volt supply, or, a fault in the AHC Pump Motor Relay (possible, test per FSM), or, if the AHC Fluid level falls too low and admits air to the AHC Pump, or,
• if there is a fault in the Fluid Pressure Sensor located on the side of the AHC Pump assembly (there is only this one pressure sensor in the AHC/TEMS system for LC100/LX470) – test per FSM as shown for C1718,
• In the case of C1762, the FSM-specified Fail Safe Function is slightly different to C1736 -- but the effect and the visible symptoms are much the same: NO self-adjusting AHC function, NO TEMS adaptive damping, AND the vehicle also may settle to “LO” height -- see attachment,

Over a period of time, work on this vehicle has included removal/replacement of all four ‘shock absorbers, all four ‘globes’, Height Control Accumulator, and some AHC tubing. All this work and the replacements mean that

• VERY LARGE AMOUNTS of air have been admitted into the AHC system, and,
• possibly made worse if air has entered at the AHC Tank if fluid level dropped too low, or, if the vehicle has been moved or rocked with bleeder screw(s) still open, or, if ANY hydraulic line in the AHC system has been opened, and,
• purging all of this air will take a LOT more repetitive bleeding effort and a LOT more persistence than the regular standard bleeding process per FSM, and/or variations developed by @PADDO and others. This can involve start/stop efforts to get air-polluted fluid through and out of the system, step by step in the short intervals before C1762 stops the pump, as reported by @aharlan001 and others in the frustrating experiences in the long lead-up to this post: AHC Inop after fluid change 2007 lx C1751 and C1762 - https://forum.ih8mud.com/threads/ahc-inop-after-fluid-change-2007-lx-c1751-and-c1762.1233088/page-13#post-13517321

What to do next?

If this were my vehicle, I would be

• very suspicious that the main problem is air still in the AHC system,
• fully aware that a major and persistent bleeding effort is necessary,
• concerned about the condition of the AHC Pump which after 22 years of service, owes me nothing,
• disinterested in a major fault-finding/bleeding effort with the ancient existing AHC Pump still in place and then finding later that I needed to break open the system again to replace or repair the pump and repeat the bleeding effort again,
• disinterested in repairing the existing AHC Pump -- clean the internal strainers, replace internal O-rings above the gear-cases, etc, etc -- this is not difficult -- been there, done that, reported on it -- can be successful but it is still a 22 years old pump with unseen wear and tear!
• interested in replacing the AHC Pump sub-assembly with a NEW pump (NOT a second-hand pump of unknown internal condition), for example new from IMPEX at USD98.29 plus delivery, plus some miscellaneous low cost items -- maybe this is a conservative approach -- the aim is reliability on a 22 years old vehicle:

48901-60010 – AHC Pump sub-assembly,
90311-10001 – oil seal between AHC Pump and Motor,
90301-70003 – large O-ring for AHC Pump outer cover of AHC Pump,
90301-06012 – small O-ring for discharge from AHC Pump sub-assembly to AHC system,
47255-60010 – grommet between AHC Tank and AHC Pump,
49189-60010 – replacement bleeder valves (5 required),
49177-60010 – replacement bleeder caps (5 required),
08886-01805 – AHC Fluid in 2.5 litre steel drums, at least two, probably three drums,

With confidence that ALL relevant components are reliable, I would

• start the engine and AHC system and persist with a very determined, repetitive bleeding process,
• use new or at least bubble-free AHC Fluid after each ‘raise’, however slow or however small the raise might be – because each time the vehicle is dropped, bubbly AHC Fluid arrives back at the AHC Tank and needs to be removed. Otherwise, as soon as the AHC Pump is started, this bubbly AHC Fluid is sent by the AHC Pump from the AHC Tank to the Height Control Accumulator and to the rest of the AHC system, polluting it with air bubbles again -- see attached diagrams of the flow paths,
• remove the AHC Fluid in the AHC Tank, open the bleeder screw on the Height Control Accumulator and empty it BEFORE it attempts to raise the vehicle -- then add new or at least bubble-free AHC Fluid to the AHC Tank,
• help the process by allowing the AHC Pump to run with each bleeder screw open one-by-one (all five bleeders but not all together -- assumes that the ECU will open the Levelling Valves within the Control Valve Assembly and the Solenoid Valve at the Height Control Accumulator),
• repeat, repeat, repeat.

Some notes on so-called ‘over-riding’ of the “fail safe functions”:

• When the Height Control Operation Test (“Active Test”) does not work, it means a fault/DTC is preventing it from working and the fault and DTC must be cleared first before this test will work properly,
• This test is designed into the system to facilitate adjustments -- it is not designed to override fault conditions nor the "Fail Safe Function",
• When the Height Control Operation Test (“Active Test”) can work correctly, the ECU causes the AHC Pump to operate and also causes the Levelling Valves in the Control Valve Assembly to open as required to allow the vehicle to be raised or lowered,
• The “Levelling Valves” (two Front, two Rear) are ‘normally closed’,
• The vehicle cannot be raised or lowered unless the Levelling Valves are caused to open by the ECU – or unless the vehicle is lowered by dumping AHC Fluid from the bleeder screws,
• Operating the AHC Pump without opening the Levelling Valves (such as by direct 12 volt connection to the AHC Pump Motor) cannot raise the vehicle because there is no signal from the ECU to the Levelling Valves to cause them to open,
• The Solenoid Valve on the Height Control Accumulator is ‘normally closed’ -- the Solenoid Valve on a healthy AHC system only opens on a signal from the ECU to open (i) when the Height Control Accumulator is required to discharge at the start of a ‘raise’ to lift the vehicle, and (ii) when the Height Control Accumulator is being re-filled at the end of a ‘raise’ in readiness for the next raise,
• The Height Control Accumulator has no other function in the operation of the AHC system,
• The ECU will not signal to the Solenoid Valve to open at the Height Control Accumulator in the presence of a prohibitive fault/DTC which results in a “Fail Safe Function”,
• When the AHC Pump is caused to operate using direct 12 volt supply against closed Levelling Valves and a closed Solenoid Valve on the Height Control Accumulator, then the AHC Fluid from the AHC Pump has nowhere to go other than some fluid forcibly bypassing/shortcircuiting internally within the AHC Pump sub-assembly, and with the pump pressure hammering on seals and valves. All that will happen is noisy cavitation within the AHC Pump. Unlike industrial gear pumps, there is no pressure relief valve to protect the AHC Pump. Instead the system relies on ECU-controlled protections such as C1718, C1C1736, C1741, C1743, C1762, C1763 to quickly shutdown the AHC Pump under FSM-specified conditions.

By the way, it is good to show the whole Techstream screenshot -- then it can be checked whether the "Main Relay Expectation" is "ON". This refers to the AHC Main Relay located at the ECU under the dashboard. If this relay is not working, operation of the AHC/TEMS is not possible. It also shows the number Diagnostic Trouble Codes (DTC's) at the time of the test.

A few diagrams and pictures:

Raising Vehicle:

Re-filling Height Control Accumulator:

Revealing AHC Pump sub-assembly Part Number 48901-60010:

 

[suprasvobodea]

Frustration+++ from @suprasvobodea and posts in two threads looking for advice. You already have learned a lot about the AHC/TEMS systems on LC100/LX470 vehicles. Here a few thoughts which may help you go further ….

Summarising the situation, as I understand it:

• 2002 LX470 at 230k miles, Texas domicile, not rusted out,
• new ‘globes’ Front and Rear, 4-5 months ago, then 12 graduations at AHC Tank on HI/LO test,
• existing ‘shock absorbers’ still serviceable, removed and replaced after fitting new bushings,
• new Height Control Accumulator installed (bleeder broken on original Height Control Accumulator),
• “new line that runs to the (Height Control?) accumulator from the fluid reservoir across the underside of the truck”. There is no such single direct line so what does this mean? The line from the AHC Pump to the Pump Attenuator? Or the Pump Attenuator itself? Or the line from the Pump Attenuator to the Control Valve Assembly? Or the line from the Control Valve Assembly to the Height Control Accumulator? Anyway, it seems that a new tube has been fitted in one of these places,
• new AHC Fluid used from steel can Part Number 08886-01805, not from problematic plastic bottles Part Number 8886-81221,
• Height Control Operation Test (“Active Test”) is not working using Techstream nor with the manual method using connections at DLC1. [Note: This test will not work if there is a fault/DTC in the AHC system, such as C1762 or C1751 etc],
• C1736 appeared initially but was cleared later,
• Note: Fail safe function for C1736: “If trouble occurs in the Control Valve Assembly circuit (BTW this includes the circuit to the Solenoid Valve at the front of the Height Control Accumulator), then the ECU prohibits the height control function and fixes the damping force at the Sports mode”. Symptoms to look for: No AHC function; VERY rough ride because TEMS damping function is FIXED at Sports mode. Could mean problem connectors, problem harness wiring, or problem components],
• Per FSM, C1736 is caused by incorrect “B” voltages as read by ECU – could be caused by faulty solenoid (new, seems unlikely, but maybe check the solenoid for internal continuity per FSM anyway), or, check loose or damaged connector (possible, so inspect, test), or, check for damaged wiring (possible, so inspect, test -- this cause is reported increasingly often as these LC100/LX470 vehicles age ), or, faulty ECU (possible but very unlikely in the absence of other symptoms elsewhere in the AHC/TEMS systems),
• Per FSM, C1762 is caused by low delivery pressure from the AHC Pump. It is a very quick-acting response -- this positive displacement gear pump stops after 0.6 seconds under the FSM-specified DTC fault conditions and then DTC C1762 is set, needs to be rectified and cleared. The design purpose is to protect the pump from excessive cavitation and internal destructive wear and damage if the pump cannot draw sufficient fluid from the AHC Tank, usually due to a partially blocked strainer on the inlet side within the pump. Blockages are increasingly likely as these LC100/LX470 vehicles age and especially if AHC Fluid has not been replaced at least as often as specified in Owners Manual, every 60,000 miles – preferably twice as often. If not done, sludge or gel accumulates in the system – especially between the pump sub-assembly Part Number 48901-60010 and the outer case with the big “+” sign on it (faces the firewall on LHD vehicles),

A similar outcome occurs if

• the AHC Pump has an ‘air-lock’, or,
• if there is entrained air or dissolved air in the AHC Fluid and the pump ‘sucks’ air (and/or tries to compress air in the system rather than pumping fluid) – in the AHC Pump this would be called ‘aeration’ rather than ‘cavitation’ but the effect on pump performance is much the same, or,
• if the internal components of the AHC Pump sub-assembly are worn or damaged and there is too much fluid bypassing above or below the gear set rather than through the gear teeth which are responsible for the pumping effort -- then there will be low pump delivery. [Aside: this is a positive displacement gear pump -- it delivers volume flow, pressure only arises if there is resistance to fluid flow], or,
• if there is a fault in the AHC Pump Motor (unlikely if the pump runs when tested on direct 12 volt supply, or, a fault in the AHC Pump Motor Relay (possible, test per FSM), or, if the AHC Fluid level falls too low and admits air to the AHC Pump, or,
• if there is a fault in the Fluid Pressure Sensor located on the side of the AHC Pump assembly (there is only this one pressure sensor in the AHC/TEMS system for LC100/LX470) – test per FSM as shown for C1718,
• In the case of C1762, the FSM-specified Fail Safe Function is slightly different to C1736 -- but the effect and the visible symptoms are much the same: NO self-adjusting AHC function, NO TEMS adaptive damping, AND the vehicle also may settle to “LO” height -- see attachment,

Over a period of time, work on this vehicle has included removal/replacement of all four ‘shock absorbers, all four ‘globes’, Height Control Accumulator, and some AHC tubing. All this work and the replacements mean that

• VERY LARGE AMOUNTS of air have been admitted into the AHC system, and,
• possibly made worse if air has entered at the AHC Tank if fluid level dropped too low, or, if the vehicle has been moved or rocked with bleeder screw(s) still open, or, if ANY hydraulic line in the AHC system has been opened, and,
• purging all of this air will take a LOT more repetitive bleeding effort and a LOT more persistence than the regular standard bleeding process per FSM, and/or variations developed by @PADDO and others. This can involve start/stop efforts to get air-polluted fluid through and out of the system, step by step in the short intervals before C1762 stops the pump, as reported by @aharlan001 and others in the frustrating experiences in the long lead-up to this post: AHC Inop after fluid change 2007 lx C1751 and C1762 - https://forum.ih8mud.com/threads/ahc-inop-after-fluid-change-2007-lx-c1751-and-c1762.1233088/page-13#post-13517321

What to do next?

If this were my vehicle, I would be

• very suspicious that the main problem is air still in the AHC system,
• fully aware that a major and persistent bleeding effort is necessary,
• concerned about the condition of the AHC Pump which after 22 years of service, owes me nothing,
• disinterested in a major fault-finding/bleeding effort with the ancient existing AHC Pump still in place and then finding later that I needed to break open the system again to replace or repair the pump and repeat the bleeding effort again,
• disinterested in repairing the existing AHC Pump -- clean the internal strainers, replace internal O-rings above the gear-cases, etc, etc -- this is not difficult -- been there, done that, reported on it -- can be successful but it is still a 22 years old pump with unseen wear and tear!
• interested in replacing the AHC Pump sub-assembly with a NEW pump (NOT a second-hand pump of unknown internal condition), for example new from IMPEX at USD98.29 plus delivery, plus some miscellaneous low cost items -- maybe this is a conservative approach -- the aim is reliability on a 22 years old vehicle:

48901-60010 – AHC Pump sub-assembly,
90311-10001 – oil seal between AHC Pump and Motor,
90301-70003 – large O-ring for AHC Pump outer cover of AHC Pump,
90301-06012 – small O-ring for discharge from AHC Pump sub-assembly to AHC system,
47255-60010 – grommet between AHC Tank and AHC Pump,
49189-60010 – replacement bleeder valves (5 required),
49177-60010 – replacement bleeder caps (5 required),
08886-01805 – AHC Fluid in 2.5 litre steel drums, at least two, probably three drums,

With confidence that ALL relevant components are reliable, I would

• start the engine and AHC system and persist with a very determined, repetitive bleeding process,
• use new or at least bubble-free AHC Fluid after each ‘raise’, however slow or however small the raise might be – because each time the vehicle is dropped, bubbly AHC Fluid arrives back at the AHC Tank and needs to be removed. Otherwise, as soon as the AHC Pump is started, this bubbly AHC Fluid is sent by the AHC Pump from the AHC Tank to the Height Control Accumulator and to the rest of the AHC system, polluting it with air bubbles again -- see attached diagrams of the flow paths,
• remove the AHC Fluid in the AHC Tank, open the bleeder screw on the Height Control Accumulator and empty it BEFORE it attempts to raise the vehicle -- then add new or at least bubble-free AHC Fluid to the AHC Tank,
• help the process by allowing the AHC Pump to run with each bleeder screw open one-by-one (all five bleeders but not all together -- assumes that the ECU will open the Levelling Valves within the Control Valve Assembly and the Solenoid Valve at the Height Control Accumulator),
• repeat, repeat, repeat.

Some notes on so-called ‘over-riding’ of the “fail safe functions”:

• When the Height Control Operation Test (“Active Test”) does not work, it means a fault/DTC is preventing it from working and the fault and DTC must be cleared first before this test will work properly,
• This test is designed into the system to facilitate adjustments -- it is not designed to override fault conditions nor the "Fail Safe Function",
• When the Height Control Operation Test (“Active Test”) can work correctly, the ECU causes the AHC Pump to operate and also causes the Levelling Valves in the Control Valve Assembly to open as required to allow the vehicle to be raised or lowered,
• The “Levelling Valves” (one Front, one Rear) are ‘normally closed’,
• The vehicle cannot be raised or lowered unless the Levelling Valves are caused to open by the ECU – or unless the vehicle is lowered by dumping AHC Fluid from the bleeder screws,
• Operating the AHC Pump without opening the Levelling Valves (such as by direct 12 volt connection to the AHC Pump Motor) cannot raise the vehicle because there is no signal from the ECU to the Levelling Valves to cause them to open,
• The Solenoid Valve on the Height Control Accumulator is ‘normally closed’ -- the Solenoid Valve on a healthy AHC system only opens on a signal from the ECU to open (i) when the Height Control Accumulator is required to discharge at the start of a ‘raise’ to lift the vehicle, and (ii) when the Height Control Accumulator is being re-filled at the end of a ‘raise’ in readiness for the next raise,
• The Height Control Accumulator has no other function in the operation of the AHC system,
• The ECU will not signal to the Solenoid Valve to open at the Height Control Accumulator in the presence of a prohibitive fault/DTC which results in a “Fail Safe Function”,
• When the AHC Pump is caused to operate using direct 12 volt supply against closed Levelling Valves and a closed Solenoid Valve on the Height Control Accumulator, then the AHC Fluid from the AHC Pump has nowhere to go other than some fluid forcibly bypassing/shortcircuiting internally within the AHC Pump sub-assembly, and with the pump pressure hammering on seals and valves. All that will happen is noisy cavitation within the AHC Pump. Unlike industrial gear pumps, there is no pressure relief valve to protect the AHC Pump. Instead the system relies on ECU-controlled protections such as C1718, C1C1736, C1741, C1743, C1762, C1763 to quickly shutdown the AHC Pump under FSM-specified conditions.

By the way, it is good to show the whole Techstream screenshot -- then it can be checked whether the "Main Relay Expectation" is "ON". This refers to the AHC Main Relay located at the ECU under the dashboard. If this relay is not working, operation of the AHC/TEMS is not possible. It also shows the number Diagnostic Trouble Codes (DTC's) at the time of the test.

A few diagrams and pictures:

Raising Vehicle:
View attachment 3549751
Re-filling Height Control Accumulator:

View attachment 3549760

View attachment 3549777

Revealing AHC Pump sub-assembly Part Number 48901-60010:
View attachment 3549779

Indocruise

Thank you, Sir, for your incredibly detailed and descriptive analysis and plan of attack for my problem. I am GREATEFUL, beyond description that you make such an effort to help fellow LC and LX470 owners fix and troubleshoot their vehicles! I agree with everything you pointed out, especially getting a NEW pump assy ( not a used one from someone who foolishly removed their AHC!)

As for my plan, I already DID ORDER a NEW PUMP Sub ASSY from IMPEX for $98 and the other o-rings and gaskets to install it. I think it was a total of $130 with shipping. however, just got an email from them saying it's back ordered and won't arrive till Feb 29th!!:-( SO... I can't report anything, .. until I get the NEW pump installed and purged.

Also, after thinking about your description of the "aerated hydraulic oil", I remembered helping my dad make apple wine in our basement in Wisconsin when I was a kid. He had a 5L Erlinmyer Vacumn flask to pull a vacuum on the apple puree he placed in a very wide-mouth porcelain funnel that sat in the open top with a rubber stopper that had a hole in it for the funnel. The point here is this,..... if you place an aerated liquid in a vacuum flask, & attach a vacuum hose to the nipple on the side, and plug the top, you will "pull" any air from the liquid OUT of it, and you are left with BUBBLE FREE fluid. I did the same thing with clear casting resin to cast coins, jewelry, anything that you want to show in a clear polyster resin. So... why am I sharing this with ya'll?? Because, if you're pouring, new clean, pink, fluid into your system and are bleeding it repetitively, you don't need to throw out perfectly good oil just because it has fine bubbles in it! Besides, at $59 for a 2.5L can and using a few cans.,.. well.. you get the picture.

So, I bought a 2000L Erlinmyer Vacumn flask for $40 on eBay or AMAZON and will pull a vacuum ( using my AC Vacumn pump)on the 1L or so of AHC oil I collect after several bleeds to reuse in my system and save .. ohh probably $120+ inexpensive AHC oil!

I'll have a report next month (March) after my new pump arrives from IMPEX in Japan.

Until then..............

 

[suprasvobodea]

Indocruise

Thank you, Sir, for your incredibly detailed and descriptive analysis and plan of attack for my problem. I am GREATEFUL, beyond description that you make such an effort to help fellow LC and LX470 owners fix and troubleshoot their vehicles! I agree with everything you pointed out, especially getting a NEW pump assy ( not a used one from someone who foolishly removed their AHC!)

As for my plan, I already DID ORDER a NEW PUMP Sub ASSY from IMPEX for $98 and the other o-rings and gaskets to install it. I think it was a total of $130 with shipping. however, just got an email from them saying it's back ordered and won't arrive till Feb 29th!!:-( SO... I can't report anything, .. until I get the NEW pump installed and purged.

Also, after thinking about your description of the "aerated hydraulic oil", I remembered helping my dad make apple wine in our basement in Wisconsin when I was a kid. He had a 5L Erlinmyer Vacumn flask to pull a vacuum on the apple puree he placed in a very wide-mouth porcelain funnel that sat in the open top with a rubber stopper that had a hole in it for the funnel. The point here is this,..... if you place an aerated liquid in a vacuum flask, & attach a vacuum hose to the nipple on the side, and plug the top, you will "pull" any air from the liquid OUT of it, and you are left with BUBBLE FREE fluid. I did the same thing with clear casting resin to cast coins, jewelry, anything that you want to show in a clear polyster resin. So... why am I sharing this with ya'll?? Because, if you're pouring, new clean, pink, fluid into your system and are bleeding it repetitively, you don't need to throw out perfectly good oil just because it has fine bubbles in it! Besides, at $59 for a 2.5L can and using a few cans.,.. well.. you get the picture.

So, I bought a 2000L Erlinmyer Vacumn flask for $40 on eBay or AMAZON and will pull a vacuum ( using my AC Vacumn pump)on the 1L or so of AHC oil I collect after several bleeds to reuse in my system and save .. ohh probably $120+ inexpensive AHC oil!

I'll have a report next month (March) after my new pump arrives from IMPEX in Japan.

Until then..............

IndoCrusise <<UPDATES>>

I finally got the NEW pump subassembly from IMPEX in Japan, (I think it was back ordered/manufactured!) since it took 4 weeks!
I cleaned the container with simple green and "purple power" after installing the new pump since it was separated.
I refilled the container half to 3/4 full with new fluid. I checked for any codes by jumping E1 & Tc. I got a 1-8 flash on the OFF light - which I believe = 1718. - The pump pressure is abnormal )Fluid Pressure sensor circuit) & I cleared it so I started fresh.
I then performed the "Active Test" by shorting the E1 & Ts in the diagnostic box on the pass. side fender. I started the vehicle and pressed the down button immediately at least 5 -10 times. The rapid flashing stopped for 3-4 seconds, then started up again. I tried to go through the table of procedures in the Service Manual ( press up, press up and hold, press down, press down and hold) NOTHING happened. None of the UP /DOWN functions worked after performing the test. I turned off the engine, disconnected the Ts jumper, and restarted the engine. I pressed the ON/OFF for a couple of seconds to clear the test. The OFF button slowed to a constant flash every second after ( not the rapid 1/4 sec which shows =NO CODE ). That is the state I left the LX470 tonight :-(


So.... I need your help! I summarized that the "Active Test " is not working. I checked the accumulator and there is no pressure or fluid at the bleeder. I understand that applying 12V directly to the pump to pressurize is NOT recommended since the leveling valves and solenoid valve on the accumulator are both closed so there is nowhere for the fluid to go! ( Thank you for that tip!)

What do I do next ....?? I'm starting to understand this system now ( but still frustrated) after several months of messing with it,.. i cant stop now! Please let me know what your experience and expert diagnostic wisdom you can share with me!

 

[suprasvobodea]

Indocruise

I did some more investigative/diagnostic work and rechecked for codes, and sure enough, I have the 1762 code back. After going through the troubleshooting checklist, the 3rd step is to check the pressure switch on the pump, first checking the voltage at the AHC computer by the driver's position RH leg. It was 5 .0V per spec. THen i checked the pressure switch voltage and it was supposed to be ~ 1.4-2.2V or something like that from the Lexus SM, Mine was 0.505 V! So seeing how that is was sent a signal to the ECU turned on the "Active Test" and released the lockout feature , it's probably the problem! So i placed another order at IMPEX for this VERY VERY expensive $232 switch. ( $478 at my local Lexus online parts dealer in Dallas)

PLEASE let me know your thoughts about this if you think this is the cause of this problem. Now, I'm not sure the new pump assembly was the problem, but after 22 years, i think it was good insurance and it will lift faster now, ... whenever I get it working again!

 

[suprasvobodea]

Indocruise

I did some more investigative/diagnostic work and rechecked for codes, and sure enough, I have the 1762 code back. After going through the troubleshooting checklist, the 3rd step is to check the pressure switch on the pump, first checking the voltage at the AHC computer by the driver's position RH leg. It was 5 .0V per spec. THen i checked the pressure switch voltage and it was supposed to be ~ 1.4-2.2V or something like that from the Lexus SM, Mine was 0.505 V! So seeing how that is was sent a signal to the ECU turned on the "Active Test" and released the lockout feature , it's probably the problem! So i placed another order at IMPEX for this VERY VERY expensive $232 switch. ( $478 at my local Lexus online parts dealer in Dallas)

PLEASE let me know your thoughts about this if you think this is the cause of this problem. Now, I'm not sure the new pump assembly was the problem, but after 22 years, i think it was good insurance and it will lift faster now, ... whenever I get it working again!

indocruise-

I'm still waiting for the pressure sensor to arrive from IMPEX in Japan. I've been doing some more analyzing, & have a question. The "active text" when it's not blocked by the fail-safe override, is THIS the manual way to prime the pump and force fluid into the accumulator and the shocks?? If, so, then the pressure sensor that I checked with ( 0.505)V has got to be what's preventing the "active Test" from functioning and the pump from pushing oil throughout the system,.. correct? When you get back, please reply to my previous posts, and this question. I am grateful for your help!

 

[suprasvobodea]

Good afternoon my AHC friends! I got around to installing some 30mm spacers this afternoon. Install was straightforward. I fired techstream up and it brought my rear pressures down by 0.5. Not quite as much as I was hoping. Also strangely whenever I would go from Lo to N or N to Hi I would hear a beep / squeak from the height accumulator about 1/2 the time. I blead a quart thought but this did not seem to help. I took it for a short drive, about 1/4 mile and the beep/squeak is gone! I can hear a hiss as the from the accumulator as the pump stops but I'm pretty sure this is normal and I can only hear it if I have the window down. Strangely I checked my grads and shockingly I went from 8-9 grads to 12-13 grads! I almost don't believe that these original 13 year old globes are giving me 12-13 grads... any thoughts??? Also I am looking to tow a 5,000 lb travel trailer maybe 200-300 miles+ 3 people this summer. Do you think my AHC can handle this with rear pressure at 6.3? Do I need new springs? Thanks! Also for anyone looking for cheap spacers you can get Nolathalen 30mm spacers part number REV170.0008 right now on ebay shipped for under 40$ most others go for 75$+

AHARLAN,

Where did you get the 30mm spaceers and what link did you use to order them? Are you in the US? What IMUD forum should I review to see how to do this job? I replaced the REAR struts by cutting a 60mm floor opening and saving HOURS of time. I will be writing up a page on where to cut the opening and some other important secrets on how to do this, 3rd most difficult job on an LX 470/ LC - ( after replacing the Accumulator and the hydraulic line that runs to it from the Pump at the passenger side firewall! )

 

[suprasvobodea]

Indocruise

Thank you, Sir, for your incredibly detailed and descriptive analysis and plan of attack for my problem. I am GREATEFUL, beyond description that you make such an effort to help fellow LC and LX470 owners fix and troubleshoot their vehicles! I agree with everything you pointed out, especially getting a NEW pump assy ( not a used one from someone who foolishly removed their AHC!)

As for my plan, I already DID ORDER a NEW PUMP Sub ASSY from IMPEX for $98 and the other o-rings and gaskets to install it. I think it was a total of $130 with shipping. however, just got an email from them saying it's back ordered and won't arrive till Feb 29th!!:-( SO... I can't report anything, .. until I get the NEW pump installed and purged.

Also, after thinking about your description of the "aerated hydraulic oil", I remembered helping my dad make apple wine in our basement in Wisconsin when I was a kid. He had a 5L Erlinmyer Vacumn flask to pull a vacuum on the apple puree he placed in a very wide-mouth porcelain funnel that sat in the open top with a rubber stopper that had a hole in it for the funnel. The point here is this,..... if you place an aerated liquid in a vacuum flask, & attach a vacuum hose to the nipple on the side, and plug the top, you will "pull" any air from the liquid OUT of it, and you are left with BUBBLE FREE fluid. I did the same thing with clear casting resin to cast coins, jewelry, anything that you want to show in a clear polyster resin. So... why am I sharing this with ya'll?? Because, if you're pouring, new clean, pink, fluid into your system and are bleeding it repetitively, you don't need to throw out perfectly good oil just because it has fine bubbles in it! Besides, at $59 for a 2.5L can and using a few cans.,.. well.. you get the picture.

So, I bought a 2000L Erlinmyer Vacumn flask for $40 on eBay or AMAZON and will pull a vacuum ( using my AC Vacumn pump)on the 1L or so of AHC oil I collect after several bleeds to reuse in my system and save .. ohh probably $120+ inexpensive AHC oil!

I'll have a report next month (March) after my new pump arrives from IMPEX in Japan.

Until then..............

IndoCruise

I finally received a new pressure switch from Japan and installed it. I cleared the 1762 code with techstream and it started pumping after I did the ACTIVE test function. The tank was getting low, so I stopped the pump by pressing the down switch to N. HOWEVER, something happened, when I restarted the test, the dreaded 1762 code returned!! I had to remove the jumper wire in the diagnostic box to clear the code with Techstream and then restart the engine, to initiate the ACTIVE test but I pressed the UP direction, not the DOWN direction. I don't know if that matters- , but now the code keeps returning.! I have cleared the code and restarted the active test by pressing DOWN, but the 1762 code keeps returning!! Now, I am lost! I checked the voltage at the pressure switch and it was 0.505 V. This is after I replaced it with the NEW switch.!??! I have tried 7 times and it keeps throwing the 1762 code. What's worse, I added another liter of oil to the reservoir when it was pumping, and when it threw the code, it fell b back to the stops and the tank overflowed about 1.2 liters of oil all over the ground!!!! :-( So I have a NEW mess to clean up.

Indocruise, what do I do next ...? I'm completely out of ideas. I have replaced TWO ( 2) pressure switches now at $250 a piece, and wasted 2 L of Oil.
QUESTION> _ How do I stop the computer from continuing to get the 1762 code?
2.) Should I bleed the accumulator and globes before resetting and clearing the error code? The truck is on the stops so there is no point as there is very low pressure in system...since all the fluid is back in the reservoir and on the ground now!!

 

[suprasvobodea]

Frustration+++ from @suprasvobodea and posts in two threads looking for advice. You already have learned a lot about the AHC/TEMS systems on LC100/LX470 vehicles. Here a few thoughts which may help you go further ….

Summarising the situation, as I understand it:

• 2002 LX470 at 230k miles, Texas domicile, not rusted out,
• new ‘globes’ Front and Rear, 4-5 months ago, then 12 graduations at AHC Tank on HI/LO test,
• existing ‘shock absorbers’ still serviceable, removed and replaced after fitting new bushings,
• new Height Control Accumulator installed (bleeder broken on original Height Control Accumulator),
• “new line that runs to the (Height Control?) accumulator from the fluid reservoir across the underside of the truck”. There is no such single direct line so what does this mean? The line from the AHC Pump to the Pump Attenuator? Or the Pump Attenuator itself? Or the line from the Pump Attenuator to the Control Valve Assembly? Or the line from the Control Valve Assembly to the Height Control Accumulator? Anyway, it seems that a new tube has been fitted in one of these places,
• new AHC Fluid used from steel can Part Number 08886-01805, not from problematic plastic bottles Part Number 8886-81221,
• Height Control Operation Test (“Active Test”) is not working using Techstream nor with the manual method using connections at DLC1. [Note: This test will not work if there is a fault/DTC in the AHC system, such as C1762 or C1751 etc],
• C1736 appeared initially but was cleared later,
• Note: Fail safe function for C1736: “If trouble occurs in the Control Valve Assembly circuit (BTW this includes the circuit to the Solenoid Valve at the front of the Height Control Accumulator), then the ECU prohibits the height control function and fixes the damping force at the Sports mode”. Symptoms to look for: No AHC function; VERY rough ride because TEMS damping function is FIXED at Sports mode. Could mean problem connectors, problem harness wiring, or problem components],
• Per FSM, C1736 is caused by incorrect “B” voltages as read by ECU – could be caused by faulty solenoid (new, seems unlikely, but maybe check the solenoid for internal continuity per FSM anyway), or, check loose or damaged connector (possible, so inspect, test), or, check for damaged wiring (possible, so inspect, test -- this cause is reported increasingly often as these LC100/LX470 vehicles age ), or, faulty ECU (possible but very unlikely in the absence of other symptoms elsewhere in the AHC/TEMS systems),
• Per FSM, C1762 is caused by low delivery pressure from the AHC Pump. It is a very quick-acting response -- this positive displacement gear pump stops after 0.6 seconds under the FSM-specified DTC fault conditions and then DTC C1762 is set, needs to be rectified and cleared. The design purpose is to protect the pump from excessive cavitation and internal destructive wear and damage if the pump cannot draw sufficient fluid from the AHC Tank, usually due to a partially blocked strainer on the inlet side within the pump. Blockages are increasingly likely as these LC100/LX470 vehicles age and especially if AHC Fluid has not been replaced at least as often as specified in Owners Manual, every 60,000 miles – preferably twice as often. If not done, sludge or gel accumulates in the system – especially between the pump sub-assembly Part Number 48901-60010 and the outer case with the big “+” sign on it (faces the firewall on LHD vehicles),

A similar outcome occurs if

• the AHC Pump has an ‘air-lock’, or,
• if there is entrained air or dissolved air in the AHC Fluid and the pump ‘sucks’ air (and/or tries to compress air in the system rather than pumping fluid) – in the AHC Pump this would be called ‘aeration’ rather than ‘cavitation’ but the effect on pump performance is much the same, or,
• if the internal components of the AHC Pump sub-assembly are worn or damaged and there is too much fluid bypassing above or below the gear set rather than through the gear teeth which are responsible for the pumping effort -- then there will be low pump delivery. [Aside: this is a positive displacement gear pump -- it delivers volume flow, pressure only arises if there is resistance to fluid flow], or,
• if there is a fault in the AHC Pump Motor (unlikely if the pump runs when tested on direct 12 volt supply, or, a fault in the AHC Pump Motor Relay (possible, test per FSM), or, if the AHC Fluid level falls too low and admits air to the AHC Pump, or,
• if there is a fault in the Fluid Pressure Sensor located on the side of the AHC Pump assembly (there is only this one pressure sensor in the AHC/TEMS system for LC100/LX470) – test per FSM as shown for C1718,
• In the case of C1762, the FSM-specified Fail Safe Function is slightly different to C1736 -- but the effect and the visible symptoms are much the same: NO self-adjusting AHC function, NO TEMS adaptive damping, AND the vehicle also may settle to “LO” height -- see attachment,

Over a period of time, work on this vehicle has included removal/replacement of all four ‘shock absorbers, all four ‘globes’, Height Control Accumulator, and some AHC tubing. All this work and the replacements mean that

• VERY LARGE AMOUNTS of air have been admitted into the AHC system, and,
• possibly made worse if air has entered at the AHC Tank if fluid level dropped too low, or, if the vehicle has been moved or rocked with bleeder screw(s) still open, or, if ANY hydraulic line in the AHC system has been opened, and,
• purging all of this air will take a LOT more repetitive bleeding effort and a LOT more persistence than the regular standard bleeding process per FSM, and/or variations developed by @PADDO and others. This can involve start/stop efforts to get air-polluted fluid through and out of the system, step by step in the short intervals before C1762 stops the pump, as reported by @aharlan001 and others in the frustrating experiences in the long lead-up to this post: AHC Inop after fluid change 2007 lx C1751 and C1762 - https://forum.ih8mud.com/threads/ahc-inop-after-fluid-change-2007-lx-c1751-and-c1762.1233088/page-13#post-13517321

What to do next?

If this were my vehicle, I would be

• very suspicious that the main problem is air still in the AHC system,
• fully aware that a major and persistent bleeding effort is necessary,
• concerned about the condition of the AHC Pump which after 22 years of service, owes me nothing,
• disinterested in a major fault-finding/bleeding effort with the ancient existing AHC Pump still in place and then finding later that I needed to break open the system again to replace or repair the pump and repeat the bleeding effort again,
• disinterested in repairing the existing AHC Pump -- clean the internal strainers, replace internal O-rings above the gear-cases, etc, etc -- this is not difficult -- been there, done that, reported on it -- can be successful but it is still a 22 years old pump with unseen wear and tear!
• interested in replacing the AHC Pump sub-assembly with a NEW pump (NOT a second-hand pump of unknown internal condition), for example new from IMPEX at USD98.29 plus delivery, plus some miscellaneous low cost items -- maybe this is a conservative approach -- the aim is reliability on a 22 years old vehicle:

48901-60010 – AHC Pump sub-assembly,
90311-10001 – oil seal between AHC Pump and Motor,
90301-70003 – large O-ring for AHC Pump outer cover of AHC Pump,
90301-06012 – small O-ring for discharge from AHC Pump sub-assembly to AHC system,
47255-60010 – grommet between AHC Tank and AHC Pump,
49189-60010 – replacement bleeder valves (5 required),
49177-60010 – replacement bleeder caps (5 required),
08886-01805 – AHC Fluid in 2.5 litre steel drums, at least two, probably three drums,

With confidence that ALL relevant components are reliable, I would

• start the engine and AHC system and persist with a very determined, repetitive bleeding process,
• use new or at least bubble-free AHC Fluid after each ‘raise’, however slow or however small the raise might be – because each time the vehicle is dropped, bubbly AHC Fluid arrives back at the AHC Tank and needs to be removed. Otherwise, as soon as the AHC Pump is started, this bubbly AHC Fluid is sent by the AHC Pump from the AHC Tank to the Height Control Accumulator and to the rest of the AHC system, polluting it with air bubbles again -- see attached diagrams of the flow paths,
• remove the AHC Fluid in the AHC Tank, open the bleeder screw on the Height Control Accumulator and empty it BEFORE it attempts to raise the vehicle -- then add new or at least bubble-free AHC Fluid to the AHC Tank,
• help the process by allowing the AHC Pump to run with each bleeder screw open one-by-one (all five bleeders but not all together -- assumes that the ECU will open the Levelling Valves within the Control Valve Assembly and the Solenoid Valve at the Height Control Accumulator),
• repeat, repeat, repeat.

Some notes on so-called ‘over-riding’ of the “fail safe functions”:

• When the Height Control Operation Test (“Active Test”) does not work, it means a fault/DTC is preventing it from working and the fault and DTC must be cleared first before this test will work properly,
• This test is designed into the system to facilitate adjustments -- it is not designed to override fault conditions nor the "Fail Safe Function",
• When the Height Control Operation Test (“Active Test”) can work correctly, the ECU causes the AHC Pump to operate and also causes the Levelling Valves in the Control Valve Assembly to open as required to allow the vehicle to be raised or lowered,
• The “Levelling Valves” (one Front, one Rear) are ‘normally closed’,
• The vehicle cannot be raised or lowered unless the Levelling Valves are caused to open by the ECU – or unless the vehicle is lowered by dumping AHC Fluid from the bleeder screws,
• Operating the AHC Pump without opening the Levelling Valves (such as by direct 12 volt connection to the AHC Pump Motor) cannot raise the vehicle because there is no signal from the ECU to the Levelling Valves to cause them to open,
• The Solenoid Valve on the Height Control Accumulator is ‘normally closed’ -- the Solenoid Valve on a healthy AHC system only opens on a signal from the ECU to open (i) when the Height Control Accumulator is required to discharge at the start of a ‘raise’ to lift the vehicle, and (ii) when the Height Control Accumulator is being re-filled at the end of a ‘raise’ in readiness for the next raise,
• The Height Control Accumulator has no other function in the operation of the AHC system,
• The ECU will not signal to the Solenoid Valve to open at the Height Control Accumulator in the presence of a prohibitive fault/DTC which results in a “Fail Safe Function”,
• When the AHC Pump is caused to operate using direct 12 volt supply against closed Levelling Valves and a closed Solenoid Valve on the Height Control Accumulator, then the AHC Fluid from the AHC Pump has nowhere to go other than some fluid forcibly bypassing/shortcircuiting internally within the AHC Pump sub-assembly, and with the pump pressure hammering on seals and valves. All that will happen is noisy cavitation within the AHC Pump. Unlike industrial gear pumps, there is no pressure relief valve to protect the AHC Pump. Instead the system relies on ECU-controlled protections such as C1718, C1C1736, C1741, C1743, C1762, C1763 to quickly shutdown the AHC Pump under FSM-specified conditions.

By the way, it is good to show the whole Techstream screenshot -- then it can be checked whether the "Main Relay Expectation" is "ON". This refers to the AHC Main Relay located at the ECU under the dashboard. If this relay is not working, operation of the AHC/TEMS is not possible. It also shows the number Diagnostic Trouble Codes (DTC's) at the time of the test.

A few diagrams and pictures:

Raising Vehicle:
View attachment 3549751
Re-filling Height Control Accumulator:

View attachment 3549760

View attachment 3549777

Revealing AHC Pump sub-assembly Part Number 48901-60010:
View attachment 3549779

I finally received a new pressure switch from Japan and installed it. I cleared the 1762 code with techstream and it started pumping after I did the ACTIVE test function. The tank was getting low, so I stopped the pump by pressing the down switch to N. HOWEVER, something happened, when I restarted the test, the dreaded 1762 code returned!! I had to remove the jumper wire in the diagnostic box to clear the code with Techstream and then restart the engine, to initiate the ACTIVE test but I pressed the UP direction, not the DOWN direction. I don't know if that matters- , but now the code keeps returning.! I have cleared the code and restarted the active test by pressing DOWN, but the 1762 code keeps returning!! Now, I am lost! I checked the voltage at the pressure switch and it was 0.505 V. This is after I replaced it with the NEW switch.!??! I have tried 7 times and it keeps throwing the 1762 code. What's worse, I added another liter of oil to the reservoir when it was pumping, and when it threw the code, it fell b back to the stops and the tank overflowed about 1.2 liters of oil all over the ground!!!! :-( So I have a NEW mess to clean up.

Indocruise, what do I do next ...? I'm completely out of ideas. I have replaced TWO ( 2) pressure switches now at $250 a piece, and wasted 2 L of Oil.
QUESTION> _ How do I stop the computer from continuing to get the 1762 code?
2.) Should I bleed the accumulator and globes before resetting and clearing the error code? The truck is on the stops so there is no point as there is very low pressure in system...since all the fluid is back in the reservoir and on the ground now!!

 

[suprasvobodea]

I finally received a new pressure switch from Japan and installed it. I cleared the 1762 code with techstream and it started pumping after I did the ACTIVE test function. The tank was getting low, so I stopped the pump by pressing the down switch to N. HOWEVER, something happened, when I restarted the test, the dreaded 1762 code returned!! I had to remove the jumper wire in the diagnostic box to clear the code with Techstream and then restart the engine, to initiate the ACTIVE test but I pressed the UP direction, not the DOWN direction. I don't know if that matters- , but now the code keeps returning.! I have cleared the code and restarted the active test by pressing DOWN, but the 1762 code keeps returning!! Now, I am lost! I checked the voltage at the pressure switch and it was 0.505 V. This is after I replaced it with the NEW switch.!??! I have tried 7 times and it keeps throwing the 1762 code. What's worse, I added another liter of oil to the reservoir when it was pumping, and when it threw the code, it fell b back to the stops and the tank overflowed about 1.2 liters of oil all over the ground!!!! :-( So I have a NEW mess to clean up.

Indocruise, what do I do next ...? I'm completely out of ideas. I have replaced TWO ( 2) pressure switches now at $250 a piece, and wasted 2 L of Oil.
QUESTION> _ How do I stop the computer from continuing to get the 1762 code?
2.) Should I bleed the accumulator and globes before resetting and clearing the error code? The truck is on the stops so there is no point as there is very low pressure in the system...since all the fluid is back in the reservoir and on the ground now!!