AHC Inop after fluid change 2007 lx C1751 and C1762

[Muhammad Rais]

Car was driving fine. Few months ago another member @IndroCruise helped me out guided me to tackle the pressure and everything was by the spec. I needed a flush since I bought the vehicle. So I decided to change it and then drive normal for 100 miles. Then all of a sudden front of the vehicle went down and rear stayed same. Sunday or Monday I will get access to tech stream and then go from there.

Yesterday fellow member came at my home and tried installing tech stream but we weren’t successful. So he plugged his laptop with my cable and it worked out. We saw the fault codes. C1751 & C1762. At that point accumulator pressure was 8.9.
After he left I tried to bleed the system. With the ignition off, I bleed driver side rear. I also filled up reservoir with another 1000ml (one full bottle). Then tried to cycle it from L to N but nothing happend. Heard the pump running then stopped and finally with OFF flashing. Then I did drain all fluid from accumulator and tried to cycle but nothing drawing from the reservoir to accumulator. Then I moved to driver side front globes. Took out all the fluid. I even tried with accumulator while open the bleed valve and started the engine but nothing was coming out of bleed valve. I ran out of time and didn’t touch passenger side. I also found pump assembly was getting hot while trying to cycle it multiple times. My reservoir has fluid way up there from max line but nothing going inside the system. Should I buy new pump assembly. What can I try at this point?

 

[ktmracer01]

From what I have read and from your last comment, it sounds like you're having a very similar issue to what @Eltestro was having on his. We bled the system numerous times after the globes were replaced and still had issues getting the system to pressurize, especially after trying to cycle it a few times.

After swapping in a pump and then pulling apart his old one, we discovered a lot of coagulated / gelatinous gunk inside the pump housing. And...the strainers in the pump appeared to be clogged. This is even after flushing several quarts (approx. 6) of brand new fluid through the system...

I replaced the internal pump unit, replaced all of the gaskets and seals, swapped it into mine and it works great now. So, I would suspect the internal pump needs to be inspected and the screens need to be cleaned. Depending on your level of mechanical ability, just replacing the internal pump might be the easiest solution.

Here's the link to all the fun we had... PNW AHC issue page-4

 

[IndroCruise]

Yesterday fellow member came at my home and tried installing tech stream but we weren’t successful. So he plugged his laptop with my cable and it worked out. We saw the fault codes. C1751 & C1762. At that point accumulator pressure was 8.9.
After he left I tried to bleed the system. With the ignition off, I bleed driver side rear. I also filled up reservoir with another 1000ml (one full bottle). Then tried to cycle it from L to N but nothing happend. Heard the pump running then stopped and finally with OFF flashing. Then I did drain all fluid from accumulator and tried to cycle but nothing drawing from the reservoir to accumulator. Then I moved to driver side front globes. Took out all the fluid. I even tried with accumulator while open the bleed valve and started the engine but nothing was coming out of bleed valve. I ran out of time and didn’t touch passenger side. I also found pump assembly was getting hot while trying to cycle it multiple times. My reservoir has fluid way up there from max line but nothing going inside the system. Should I buy new pump assembly. What can I try at this point?

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.

 

[Muhammad Rais]

finally connected tech stream. After multiple fluid flashes nothing changed. Then I followed as someone here suggested open bleed valve and strat rig and runs 5 seconds. After I did that all 5 corners rig was able to go up only at the rear with cycle. Then I did little trick, I placed my wheel jack under the car and raised it. Then once I moved the jack from the front it stayed up at the front too and car shows N. I tried to go up but it fails and come back to N. Today I again did flush all 5 corners with no visible bubbles. Above are the screen shot. Car is moving up in the rear but nothing at the front. So I tried multiple active test with diagnostic port. Not sure how to do the utility test using tech stream. I tried to select signal then select one signal but it comes with error messages and OFF flashed at the dash. Each time I did active test front pressure number changes. When I started it was at 2.2 and now finally at 5.1. Accumulator and tear pressure stayed at the same.
what should I try at this point. Trying accomplish as much I can today cause leaving again for 5 days for work tonight. Any input will be helpful. So far reading this thread more than 10 times helped me to come so far.

 

[Muhammad Rais]

Car went to H
Here is the TT shot on H

 

[Muhammad Rais]

Went to N and no OFF flashing light

 

[Muhammad Rais]

Car went to L with no flashing OFF light

 

[Muhammad Rais]

Pump ran for 1:20 seconds from L to N but didn’t stay in N. Went back to L but no flashing light OFF. Seems like pump is getting hot. So I will wait to cycle again. Also only one code now 1751 continues current to compressor motor

 

[Muhammad Rais]

After waited for 15 minutes I tried to go to N from L. And it went to N. No flashing Off light. Here is the TS shot

 

[Muhammad Rais]

I bleed 2 more times including accumulator. Not all the way to bump stop. Few ounces from each globes and accumulator.
here is the new TS shot. Also it failed twice going from L to N. 3 rd time it went to N.

here is the final process for utility check I followed.
clicked on utility on TS
Select Signal check and click next
There are two options in next window, 1. All signal check; 2. One signal check. I choose one signal check and hit next

I choose enter signal check and clear DTC, hit next

Has OFF flashing light and in TS shows

So what is the sequence I can do the utility bleed? Going to stop here for the week. Once I come back I will follow you guys experience and go from there. Again thanks to everyone who helped me so far. At least car is up not in the ground anymore.

 

[Muhammad Rais]

Bubbles were coming out of the globes when there was not much fluid left.

 

[suprarx7nut]

Bubbles were coming out of the globes when there was not much fluid left.

1. It appears you have a lot of gas trapped in that system. Probably not a good idea to leave the bleeder open like that. As soon as fluid stops flowing out, you need to close that bleeder valve immediately. Otherwise you're just allowing air to trickle back up in to the system. That bleed tube should be 100% liquid with zero bubbles. When done properly, the fluid movement is invisible because it's perfectly liquid.
2. That fluid temp is way too hot. Poor pump is working itself to death. Should be <150F in my experience.
3. I suspect you've got gunk in your pump strainers and/or massive amounts of gas. You can take your pump apart to clean out the strainer(s) (be sure to get new orings on hand) or throw in a known good pump.

 

[Muhammad Rais]

1. It appears you have a lot of gas trapped in that system. Probably not a good idea to leave the bleeder open like that. As soon as fluid stops flowing out, you need to close that bleeder valve immediately. Otherwise you're just allowing air to trickle back up in to the system. That bleed tube should be 100% liquid with zero bubbles. When done properly, the fluid movement is invisible because it's perfectly liquid.
2. That fluid temp is way too hot. Poor pump is working itself to death. Should be <150F in my experience.
3. I suspect you've got gunk in your pump strainers and/or massive amounts of gas. You can take your pump apart to clean out the strainer(s) (be sure to get new orings on hand) or throw in a known good pump.

Thanks for your reply. Bubbles were coming out like that before I have done multiple flush. Now it has fluid all the time (globes). Where as accumulator, once I open valve very little fluid comes out but then if I start the car it starts to push fluid through accumulator.
I am planning to order a pump sub assembly and two o rings. Which will take some time to come from Dubai. In the meantime I will keep flushing for fresh fluid. What I found so far. Once I open the bleed valve and starts engine then I get good flow of fluid.

 

[IndroCruise]

Thanks for your reply. Bubbles were coming out like that before I have done multiple flush. Now it has fluid all the time (globes). Where as accumulator, once I open valve very little fluid comes out but then if I start the car it starts to push fluid through accumulator.
I am planning to order a pump sub assembly and two o rings. Which will take some time to come from Dubai. In the meantime I will keep flushing for fresh fluid. What I found so far. Once I open the bleed valve and starts engine then I get good flow of fluid.

Hi @Muhammad Rais – your PM is acknowledged belatedly with apologies. I will respond here as a post so that others can critique as they see fit. The good news is that your vehicle certainly can be fixed and AHC/TEMS ride quality certainly can be restored. The bad news is that the current problems are not entirely clear and it is possible that there may be more than one problem ….

Congratulations on the perseverance and very determined progress so far – and deep sympathy for all the frustrations!!

It is good that Techstream is working again and that you have done so many tests – these provide a lot of data to consider and this is helpful.

It seems like you have put a lot of effort towards removing air from the system.

Thinking more about your vehicle, its age and location, and the symptoms and the new information ….

• 2000 LX470 model, ~250,000 miles travelled, located in Texas.

• AHC/TEMS system was working properly until recently, but deteriorated suddenly 100 miles after bleeding the system,

• Age and condition of current ‘globes’ is unknown. Has there been a ‘globe’ condition test? (This means at correct AHC pressures, observe and record difference in graduations at AHC Tank between “HI” and “LO” heights: 14 graduations = ‘globes’ near new; 7 graduations = ‘globes’ due for replacement).

• How old are the ‘globes’? It is possible that the sudden change in AHC performance 100 miles after bleeding is due to one or more ancient ‘globes’ giving up, releasing nitrogen gas into AHC system? Or that air entered the system during a bleeding event?

• In all your tests after this deterioration, the system either is slow to respond or it responds inconsistently.

Looking at the Techstream readings in the last test (your Post #290 this thread):

-0.1 inches – Front Right Height Control Sensor reading
-0.1 inches – Front Left Height Control Sensor reading
-0.1 inches – Rear Height Control Sensor reading

All OK – within FSM range 0.0 inches +/- 0.2 inches

6.7 Mpa – Front AHC Pressure – OK – within FSM range 6.4 Mpa to 7.4 Mpa,
6.0 Mpa – Rear AHC Pressure – OK – within FSM range 5.6 Mpa to 6.7 Mpa

However, correct AHC pressures by themselves tell nothing about internal condition of the ‘globes’. The “globe condition test” is necessary as mentioned above.

7.4 Mpa – Height Control Accumulator Pressure – NOT OK – very low, expect around 10.5 Mpa, means that AHC Pump has not completed re-charging the Accumulator. Accumulator pressure of 10.4 Mpa was reported prior to the recent deterioration.

• You have commented previously that the pump motor feels hot after previous multiple tests. In these more recent tests (your Post #284 to Post #290), the fluid temperature on Techstream is getting very high, sometimes up to 201 degrees Fahrenheit. As mentioned by @suprarx7nut, maybe this is due to the Pump struggling. Or maybe it simply is due to a lot of pump operation during tests repeated one after another. More usual temperatures would be around 100 degrees Fahrenheit, maybe up to 150 degrees Fahrenheit after a lot of Pump operation. The Techstream measurement comes from the temperature sensor on the AHC Pump body.

• The video at your Post #290 indicates that there is air or gas remaining in the system despite all efforts so far. It is unknown whether this is air which has entered when bleeding system, OR, whether this is nitrogen from failed ‘globes’?

• Your notes at Post #293 indicate there is more fluid flow from the Height Control Accumulator when the engine is running. This is to be expected – it means that the solenoid valve at the front of the Accumulator is open and the AHC Pump is trying re-charge the Accumulator with fluid.

• Your vehicle is pre-2002 manufacture and may be subject to a problematic O-ring in the Height Control Accumulator breaking up and causing a partial pump blockage -- see attached Technical Service Bulletin (TSB) CP-3006.

Suggestions:

• If possible, find out age of the current ‘globes’.

• If vehicle will raise to “HI”, conduct ‘globe’ overall condition test (at correct AHC pressures, record difference in graduations at AHC Tank between “HI” and “LO” heights and advise results: 14 graduations = ‘globes’ near new; 7 graduations = ‘globes’ due for replacement).

• Subject to the above HI/LO Test, or if ‘globes’ are of unknown age, consider replacement of all ‘globes’,

• Also as mentioned by @suprarx7nut, when bleeding, open and then close bleeder valves while there is flow out of the system under pressure, to ensure that there is no possibility of air or nitrogen in the plastic bleeding tube wandering back into the system.

• To be clear, air (or nitrogen) is removed from the AHC system only when the flow in the clear plastic bleeding tube contains no bubbles AND the discharge from the plastic tube into a container does not cause a froth. (A froth means tiny bubbles of absorbed gas is being is released from the fluid when it is not under any pressure other than atmospheric pressure).

• If the Height Control Accumulator has not re-charged (meaning has not refilled with fluid to a pressure around 10.5 Mpa) after raising “LO” to “N” or “N” to “HI”, then there will be minimal fluid in the Accumulator and minimal fluid will be released when bleeding the Accumulator. An Accumulator in a healthy AHC system should be re-charged by the AHC Pump within about 15 seconds after the dashboard green indicator light has stopped blinking after a raise BUT allow about 60 seconds for age and wear in an older system, OR wait until it is obvious that the AHC Pump has stopped operating and the suspension has settled.

• Hot Pump and slow re-charge of Height Control Accumulator to the expected pressure (~10.5 Mpa) may be due to slow response while compressing air (or nitrogen) remaining in the system despite efforts to remove it, OR, may be due to partial blockages in the AHC Pump impeding pump performance, as illustrated in the references mentioned at my Post #280 in this thread.

• For a vehicle 21 years old and 250,000 miles, it is not too soon to clean or replace the AHC Pump. This is a good maintenance for long term reliability. It is not a waste of time and money.

• This will mean emptying the AHC Tank and de-pressurising the system by opening bleed valves, then slowly and carefully loosening and then disconnecting the hydraulic line at the AHC Pump. Slowly, because if there is any pressure locked in this line, it will be released when it is loosened and disconnected. In a Left Hand Drive vehicle, the AHC Pump faces the firewall so it is best to remove the whole assembly using the procedure described by @BullElk at AHC pump removal with pics - https://forum.ih8mud.com/threads/ahc-pump-removal-with-pics.1227554/

• The AHC Pump itself can be disassembled and cleaned, including the small internal strainers, as mentioned in the references back at my Post #280 in this thread. If a secondhand AHC Pump is acquired, then consider dis-assembly for inspection and cleaning for confidence before installing the pump.

• Alternatively, buy a new replacement AHC Pump (Toyota/Lexus Part Number 48901-60010 (Price example: Partsouq in UAE: USD164.94 plus freight, or consider amayama or megazip, or consider local supplier).

• If replacing the pump, ideally replace associated O-rings Part Numbers 90301-70003 and 90301-06012 and the seal Part Number 90311-10001 between the pump and the motor.

• After re-installing the AHC Pump & Motor assembly back in the vehicle, it will be necessary to completely bleed the entire AHC system again. It may be necessary to prime the pump (meaning, fill it with fluid so that it can start -- zero pressure in any empty pump will be seen by the pressure sensor and will prevent the pump starting). Do this either by direct battery connection for say 10 seconds or by using the “Active Test” procedure.

• If the ‘globes’ are to be replaced, or if the AHC Pump is to be replaced, there is not much point doing any more bleeding until the after the replacements are installed.

 

[ramangain]

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!

 

[blips]

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!

Old thread but posting in case others are in this situation.

Just another obvious thing to check based on my first time flushing the system on my '98 LX - Make sure you're not getting any leakage at the bleeders after you're done with the bleeding process. I bled (shearing off accumulator bleeder in the meantime, another issue) and then tested. Got very inconsistent success cycling between L, N, H. Inspected the bleeders and found a couple of them seeping a small amount of fluid. Was hard to notice right away because I doused them with WD-40 before cracking them open.

I re-bled and got some air out - which probably got in when going from H back to N and then L, and tightened them down harder. Did this a couple times and it fixed the issue.

However, it would have been better to replace the bleeders rather than over-tightening them. I might have screwed up the threads. My bleeders are pretty corroded, so I should have replaced anyway. We'll see next time I bleed and attempt to install new bleeders.

Lesson learned: if you're fixing to bleed an old truck AHC take a close look at the bleeders. If they look old at all order new ones before you start the job.

 

[Muhammad Rais]

Hi all, today I left from work and 3 minutes away from home my rig went to low by itself. I turned around and came back. Put the car in the level ground but it’s not going up anymore. I heard and touched the AHC pump which is working but it stays on low and after trying OFF switch comes on. Please let me know where should I start looking. I didn’t work on AHC since last fluid flashes which is more than a year now. Any suggestions will be highly appreciated. I need my car for work. If I ditch AHC what are my options? Thanks for your time.

 

[uHu]

Hi all, today I left from work and 3 minutes away from home my rig went to low by itself. I turned around and came back. Put the car in the level ground but it’s not going up anymore. I heard and touched the AHC pump which is working but it stays on low and after trying OFF switch comes on. Please let me know where should I start looking. I didn’t work on AHC since last fluid flashes which is more than a year now. Any suggestions will be highly appreciated. I need my car for work. If I ditch AHC what are my options? Thanks for your time.

You start by connecting TechStream to read the values, and do a visual inspection of height sensors and linkages.

 

[Muhammad Rais]

You start by connecting TechStream to read the values, and do a visual inspection of height sensors and linkages.

 

[Muhammad Rais]

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.