LX470 AHC issues - pressure sensor 1998 Vs. 2002 (2 Viewers)

[suprarx7nut]

2001 LC

PLEASE SEE MY ANSWERS IN RED TO YOUR STATEMENTS/QUESTIONS ABOVE. What is IIRC ..?
Update after 2 hr of diagnostic fun :
I started doing the electrical troubleshooting per your suggestion
I disconnected the Accumulator 2-pin connector and checked impedance through all the intermediate connectors directly to the AHC ECU pin #24 (SLB) and pin 6 (SLAC) on the AHC ECU. I got 3 ohms on both leads from the connector back to the ECU so they are good! Also got 3 ohms on the 3 wires on the pressure switch connector back to the ECU. That is the only connector I touched besides the 3 pump connectors in the engine bay.
I think I found that gray connector in the DS rear axle on top of the frame, but it is even MORE inaccessible than the top of the strut that I cut a hole to access the top two 10 mm bolts and end cap! I too had to raise the rear with jack stands, as my LX is resting on the stops (and is as low as a Corvette now,). Please let me know if anyone can tell me HOW to access this large gray connector that rests on top of the frame rail on the driver's side I might try to disconnect it, but it may not be worth it. I don't think I need to go there, as the system DID WORK with a new PS after I installed it and I ran the reservoir to almost empty and heard that "noise " of an empty tank! and shut down the engine.
I cleared the 1762 code and as soon as I turned on the car and did the active test by pushing the DOWN switch, it immediately got 1762.

Im again past frustrated and ready to sell this damn thing. The electrical wire issue I tried ( between the Accumulator and ECU was good. ) I can't access the large gray connector on top of the frame on the Drives side rear wheel ( per 2001LC -body-off-frame pictures in post

The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-13#post-14465654

from 2001 LC is nice, but the truck's body is removed! Since my LX was working before I opened up the system and replaced everything, and I didn't touch anything electrical under the back rear vehicle ( just the midsection to remove the supply line from the accumulator to the pump attenuator by the PS frame- due to a rounded flare nut!!!! ).

If ANYONE reading this thread has any more specific ideas about specific connectors or impedance checks on specific wire harnesses per the TSM or your own experience, PLEASE let me know. I truly appreciate all the suggestions so far and have implemented them ( except for that large gray rear connector on top of the DS rear frame rail- as explained above)

All I can think of anymore ., is to wait till another new PS arrives, install it, fill the reservoir, start the LX with the ACTIVE TEST, and see if it will work again. I am truly at the end of my game here and don't know what to try to think to do anymore...... I wish one of you guys was close to Dallas TX. I would like to meet you first of all, and then tackle this problem, in the flesh until we beat it int submission.

Did you manually run the pump this afternoon?

I think this is all a looooooooot of conversation about nothing, haha. You've got gas, my man.

I'm anxious to hear what comes of this.

This all makes me almost want to purposefully run mine dry and fill it with gas just to work up a few ways to clear it out.... almost, haha.

 

[suprasvobodea]

Did you manually run the pump this afternoon?

I think this is all a looooooooot of conversation about nothing, haha. You've got gas, my man.

I'm anxious to hear what comes of this.

This all makes me almost want to purposefully run mine dry and fill it with gas just to work up a few ways to clear it out.... almost, haha.

Supra RX

It's not quite "nothing" to me when you have an LC or LX that cannot be driven for 3 months because a silly program is blocking me from running the system to purge it of air.!!!

I think I have spent quadruple the time on my LX as I did on my MK III 87 Supra Turbo last year diagnosing why I couldn't get it started! I FINALLY got lucky when I accidentally bumped the 4-pin connector for the Ignitor and it started. I tried replacing it with a different ignitor, a different coil pack, and just about every electrical part involved in the system,.... only when I accidentally moved the connector, did it work . Simple,.. just order a new auto connector from Corsa Technic with the pins, cut off the old one, and install a new, one... IT STARTS NOW .. every time!

OK, I just had to write about some of my success.... as this is kicking my ass and I'm getting depressed.

I didn't run the ACTIVE TEST yet, but I did apply 12V to the pump for 4-5 mins to try to pump oil to the accumulator, but the reservoir tank did NOT go down. The pump made a nice, normal humming sound, but I didn't see the oil level go down.. . which I thought was odd.

OK, now for the next discovery today........, Want to hear about the NEW strange thing I heard coming from the reservoir this afternoon after manually running the pump ??, I almost recorded it with my phone, to play back but I didn't have it on me. It sounded like I was hearing a "gurgling or popping sound" coming from under the reservoir. I did not see any bubbles when I looked into the tank with the cap removed,.. so I couldn't figure it out. Does anyone know or hear of this sound coming from the reservoir tank ...? WHat does this mean....? Besides air is present in the system :-)

 

[suprarx7nut]

Supra RX

It's not quite "nothing" to me when you have an LC or LX that cannot be driven for 3 months because a silly program is blocking me from running the system to purge it of air.!!!

I think I have spent quadruple the time on my LX as I did on my MK III 87 Supra Turbo last year diagnosing why I couldn't get it started! I FINALLY got lucky when I accidentally bumped the 4-pin connector for the Ignitor and it started. I tried replacing it with a different ignitor, a different coil pack, and just about every electrical part involved in the system,.... only when I accidentally moved the connector, did it work . Simple,.. just order a new auto connector from Corsa Technic with the pins, cut off the old one, and install a new, one... IT STARTS NOW .. every time!

OK, I just had to write about some of my success.... as this is kicking my ass and I'm getting depressed.

I didn't run the ACTIVE TEST yet, but I did apply 12V to the pump for 4-5 mins to try to pump oil to the accumulator, but the reservoir tank did NOT go down. The pump made a nice, normal humming sound, but I didn't see the oil level go down.. . which I thought was odd.

OK, now for the next discovery today........, Want to hear about the NEW strange thing I heard coming from the reservoir this afternoon after manually running the pump ??, I almost recorded it with my phone, to play back but I didn't have it on me. It sounded like I was hearing a "gurgling or popping sound" coming from under the reservoir. I did not see any bubbles when I looked into the tank with the cap removed,.. so I couldn't figure it out. Does anyone know or hear of this sound coming from the reservoir tank ...? WHat does this mean....? Besides air is present in the system :-)

The situation isn't nothing. But if it's gas in the lines then the electrical talk is "nothing". Just a complicated distraction.

The gurgle sounds might be fluid and gas working their way through the plumbing.

If you already ran the pump backwards for a few seconds in between forward attempts I'd try pulling the pump out and checking that inlet screen(s). I wonder if you've got debris or gel caught up in that inlet.

Nice work running the pump though. Sounds like its healthy and now we know not much is changing with a long run time. Time to check the inlet.

 

[suprasvobodea]

The situation isn't nothing. But if it's gas in the lines then the electrical talk is "nothing". Just a complicated distraction.

The gurgle sounds might be fluid and gas working their way through the plumbing.

If you already ran the pump backwards for a few seconds in between forward attempts I'd try pulling the pump out and checking that inlet screen(s). I wonder if you've got debris or gel caught up in that inlet.

Nice work running the pump though. Sounds like its healthy and now we know not much is changing with a long run time. Time to check the inlet.

Supra RX

I replaced the pump assy with a new one from IMPEX just 1 month ago, and I have all NEW oil from the cans, so I'm puzzled as to how the new screen could be plugged with NEW, fresh pink oil? There is no way that the new pump screens are clogged. I did switch the + & - on the power switch to run it backward but I didn't hear anything when I did that, it just kinda stopped moving altogether. The popping or clicking noise I will try to record tomorrow, but I'm not sure now IF I can even download a video to this platform. If I can,& you know how, please let me know how to do this

 

[suprarx7nut]

Supra RX

I replaced the pump assy with a new one from IMPEX just 1 month ago, and I have all NEW oil from the cans, so I'm puzzled as to how the new screen could be plugged with NEW, fresh pink oil? There is no way that the new pump screens are clogged. I did switch the + & - on the power switch to run it backward but I didn't hear anything when I did that, it just kinda stopped moving altogether. The popping or clicking noise I will try to record tomorrow, but I'm not sure now IF I can even download a video to this platform. If I can,& you know how, please let me know how to do this

Have you used any fluid from a plastic bottle in the last 3-4 years? The contaminated bottles will clog a brand new pump with a clear gel in a heartbeat. The screen is so small I suspect a single bottle contaminated fluid could clog 10 pumps.

If you've only used metal cans, a clogged pump does seem unlikely. In that case I'd focus on breaking lines downstream loose. See if you can provide an escape path for that gas.

 

[suprasvobodea]

Have you used any fluid from a plastic bottle in the last 3-4 years? The contaminated bottles will clog a brand new pump with a clear gel in a heartbeat. The screen is so small I suspect a single bottle contaminated fluid could clog 10 pumps. NO,only the metal can.

If you've only used metal cans, a clogged pump does seem unlikely. In that case I'd focus on breaking lines downstream loose. See if you can provide an escape path for that gas.

If I open the bleeder on the Accumulator and manually apply 12V to the pump, shouldn't I be spraying oil all over the underside of the LX from the cracked accumulator bleeder ..?
When I ran the 12V directly and loosened up the bleed screw on the accumulator, with a hose attached to it in a bottle to collect it.......... NOTHING CAME out! or even leaked on the ground. I guess I need to lose the outlet line from the pump tomorrow and start the motor to see if oil is forced out .. from there.! I know it will drip out .

 

[suprarx7nut]

If I open the bleeder on the Accumulator and manually apply 12V to the pump, shouldn't I be spraying oil all over the underside of the LX from the cracked accumulator bleeder ..?
When I ran the 12V directly and loosened up the bleed screw on the accumulator, with a hose attached to it in a bottle to collect it.......... NOTHING CAME out! or even leaked on the ground. I guess I need to lose the outlet line from the pump tomorrow and start the motor to see if oil is forced out .. from there.! I know it will drip out .

I'm honestly not sure what the valve positions will be so I can't say if you'd get pressure at the accumulator.

I'd just work my way around and see if you can expose any significant air pocket. Any line should immediately drip oil. If it doesn't, that's a great indicator that there's an air pocket hanging out. You should get oil coming out of the outlet line at the pump readily. If not, the pump isn't sucking up any fluid - @BullElk found a new o-ring helped, but I'm also still just thinking debris in that inlet screen - even if the pump is new.

If you can, document your steps and share here ( or in a clean, new thread). I'm much more of a haphazard helper here, but @2001LC, @uHu and @IndroCruise are very meticulous and if you lay out what you're doing step by step and results along the way, they may spot something helpful too.

 

[suprasvobodea]

I'm honestly not sure what the valve positions will be so I can't say if you'd get pressure at the accumulator.

I'd just work my way around and see if you can expose any significant air pocket. Any line should immediately drip oil. If it doesn't, that's a great indicator that there's an air pocket hanging out. You should get oil coming out of the outlet line at the pump readily. If not, the pump isn't sucking up any fluid - @BullElk found a new o-ring helped, but I'm also still just thinking debris in that inlet screen - even if the pump is new.

If you can, document your steps and share here ( or in a clean, new thread). I'm much more of a haphazard helper here, but @2001LC, @uHu and @IndroCruise are very meticulous and if you lay out what you're doing step by step and results along the way, they may spot something helpful too.

OK, I'll try that tomorrow ... The new PS should be in from IMPEX next week sometime. THATS what I am waiting and praying WORKS to finally END THIS NIGHTMARE!

 

[IndroCruise]

WITH LATE EDITS ADDED:

Given the previous descriptions, there is no room for doubt that there is air in the AHC system -- which makes this the first cause of DTC C1762 to pursue as held all along by @suprarx7nut [but this is not the only possible cause, other examples exist such as

• example by @BullElk (worn internal O-rings between the gear carriers and the top-plate of the pump sub-assembly),
• example by @IndroCruise and others (fully or partially blocked Inlet Strainer just before the gears inside the pump with many previous posts and pictures given on this topic),
• possible Pressure Sensor failure (extremely rare, not experienced by AHC professionals such as @suprarx7nut and @2001LC, not found by Search in IH8MUD100 series Forum,
• DTC C1762 also has been reported in parallel with other DTC's and conditions which were the root cause.

@suprarx7nut recommends clearing air from system by direct connection of the AHC Pump Motor to a 12 volt battery and running the air out through one or more bleeders.

[The intention to start the attempt with the bleeder at the Height Control Accumulator certainly is a very good idea -- once air-infected fluid is in the Height Control Accumulator, it is sent throughout the system and infects everything when the Height Control Accumulator next participates in raising the vehicle. Eventually, the air-infected fluid returns to the AHC Tank (except for the portion trapped in various places in the system) – and in the AHC Tank it may dissipate to atmosphere, or, the air-infected fluid may be sent through the system again!]

@2001LC also suggests just try the direct 12 volt connection and see what happens.

@Moridinbg reported at Post #251 at The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-13#post-14466838 that he had tried this and it did not work for him (as also noted in my previous post #34 in this this thread) -- with other experiences further described by @Moridinbg in his subsequent post #50, next below in this thread.

@IndroCruise (me) is sceptical for reasons given previously about whether direct 12 volt connection would work -- also sceptical that the solenoid valve on the Height Control Accumulator will open without the required signal from the ECU.

LATE EDITED NOTE 1: If there has been no bleed from a working bleeder at the Height Control Accumulator, then there is no fluid in the Height Control Accumulator -- or possibly (but unlikely) the Height Control Accumulator is faulty** -- meaning that it is much more likely that the AHC Pump HAS NOT re-charged the Height Control Accumulator.

**LATE EDITED NOTE 2: Note that Height Control Accumulators pre-November 2002 are the subject of the warning in Technical Services Bulletin Reference CP-3006 (attached) which specifically advises of breakdown of an O-ring within the Height Control Accumulator, leading to blockage of the Inlet Strainer inside the AHC Pump and which specifically nominates DTC C1762. However, the Height Control Accumulator was replaced with new OEM in 2023.

For all of that, I would be VERY happy -- in fact delighted -- to be proved wrong on all and any of the above issues. It certainly would make clearing air and gas problems sooo much easier!!

If the Levelling Valves and/or the Height Control Accumulator Solenoid Valve (on Techstream: SLFL = SoLenoid Front Levelling; SLRL = SoLenoid Rear Levelling; (Left and Right are not distinguished on Techstream); and SLAC = SoLenoid ACcummulator) are preventing fluid discharge from the AHC Pump, then strange noises are entirely unsurprising from a churning positive displacement gear pump.

When the AHC Pump operates, as a Gear Pump it must force fluid to flow somewhere, or stop, or break -- like any other Gear Pump, large or small. Several DTC protections exist on the AHC Pump because, unlike industrial gear pumps, there is no pressure relief valve protecting the AHC Pump. Unlike some other kinds of pumps (such as a centrifugal pump) a Gear Pump requires actual movement of fluid and cannot simply churn in an incompressible liquid.

If the discharge is blocked or valves are closed downstream, the only fluid routes available to the AHC Pump are via the clearances around the gear cases and gear shafts inside the Pump, then through the Bypass Strainer and back to the Pump Inlet Strainer, probably with some cavitation along the way -- or maybe -- directly across the top and bottom planes of the gears and around the gear perimeter if there has been enough wear to provide sufficient clearances. Whatever, any of these are very high resistance paths, pump performance will be poor and also very noisy.

Just to be clear. This is not a competition. It is an international effort by different people volunteering their own time, experience and energies to help find a solution by exploring different ideas and opinions. Better advice will not be found elsewhere!

Suggested next steps:

1. [LATE EDIT]: A replacement Pressure Sensor is on the way -- suggest for self-satisfaction double check that it is correct Part Number for the vehicle VIN, then install after conducting the FSM test procedure to ensure that the test voltages are in the correct range of 1.48 volts to 1.85 volts. If this is successful in overcoming the current breakdown -- GREAT!! We all learn something. If not successful, then the following further steps are suggested:
2. Break the line at the AHC Pump discharge and/or after the Attenuator (below the Pump) and check for positive discharge from the AHC Pump with direct connection to the 12 volt battery,
3. Persist with multiple repetitions of clearing DTC C1762 and re-starting over and over again to see whether flow can be developed and vehicle height maintained,
4. Consider gel blockage of the Inlet Strainer inside the AHC Pump sub-assembly OR the kind of Inlet Strainer blockage advised in TSB CP-3006, if that is relevant to the Manufacture Date of the Vehicle or the Height Control Sensor -- check the date code on the Accumulator with the information in TSB CP-3006,
5. Further ideas will follow later ….. including discussion of ideas by @2001LC on harness and wiring issues -- enough for now at 9:06pm in Eastern Australia.

Frustrations by @suprasvobodea are understood and respected -- we have all been there during the 'learning process'!!

 

[Moridinbg]

If I open the bleeder on the Accumulator and manually apply 12V to the pump, shouldn't I be spraying oil all over the underside of the LX from the cracked accumulator bleeder ..?
When I ran the 12V directly and loosened up the bleed screw on the accumulator, with a hose attached to it in a bottle to collect it.......... NOTHING CAME out! or even leaked on the ground. I guess I need to lose the outlet line from the pump tomorrow and start the motor to see if oil is forced out .. from there.! I know it will drip out .

There is a solenoid (SLCA in Techstream) that opens and closes the valve between the Accumulator and the pump. If you apply 12V in the expected direction (+ is the bottom pin, negative i the top on the motor plug) it will very quickly (<1sec) reach high pressure with a loud knock. I do not recommend keeping power in that way. I have toyed with the idea to manually open the solenoid and then apply power to the motor, but not yet

I have had some success with applying reverse polarity to the motor plug (negative bottom, positive top pin) for 5-7 seconds, which usually allows the system to pressurise for a while. In my case the issue is air in the fluid and accumulator with a broken off bleeder. Sometimes I have to run it in reverse 4-5 times to be able to lift it to N and rise pressure in the Acc.

 

[IndroCruise]

There is a solenoid (SLCA in Techstream) that opens and closes the valve between the Accumulator and the pump. If you apply 12V in the expected direction (+ is the bottom pin, negative i the top on the motor plug) it will very quickly (<1sec) reach high pressure with a loud knock. I do not recommend keeping power in that way. I have toyed with the idea to manually open the solenoid and then apply power to the motor, but not yet

I have had some success with applying reverse polarity to the motor plug (negative bottom, positive top pin) for 5-7 seconds, which usually allows the system to pressurise for a while. In my case the issue is air in the fluid and accumulator with a broken off bleeder. Sometimes I have to run it in reverse 4-5 times to be able to lift it to N and rise pressure in the Acc.

Hi @Moridinbg,

Yes -- another long post -- apologies in advance ….

Noted your observations: “I have had some success with applying reverse polarity to the motor plug (negative bottom, positive top pin) for 5-7 seconds, which usually allows the system to pressurise for a while. In my case the issue is air in the fluid and accumulator with a broken off bleeder. Sometimes I have to run it in reverse 4-5 times to be able to lift it to N and rise pressure in the Acc”.

Over the years, I have followed your threads on your massive “Body-Off Re-build” and also your very adventurous “South American Trip” and other posts -- and all the experience and knowledge that came with all of that. I am in no doubt whatsoever about your above observations.

May I please request your further insights??

I keep looking at my pictures and the diagrams I have prepared over years and also I have disassembled and stared at an old AHC Pump I have in my shed.

At the moment I am trying to figure out what actually happens when the AHC Pump is run in reverse.

Would this mean that the Pump Discharge to the AHC system then becomes the Inlet for all practical purposes?

I have wondered whether this would imply that AHC Fluid then is drawn into the Pump from pipework? Or somehow fluid is drawn from distant parts in the AHC system -- such as the Height Control Accumulator, ‘globes’, ‘shock absorbers’ – and if so, the various solenoid valves -- SLRL, SLFL and SLAC – must somehow allow this to happen?

However, the above idea makes no sense at all and does not fit your observations.

Clearly you have observed discharges and pressure rises in the line, sufficient to raise the vehicle in the circumstances you have described.

So is it more likely that the following happens when the Pump is run in reverse??

1. AHC Fluid floods into the AHC Pump, gravity-fed from the AHC Tank in the usual way,
2. The fluid enters the Inlet Strainer in the usual direction and then enters the gear chamber – but then passes through the middle of the Pump between the two gears while the Pump is operating in reverse, instead of around the outer perimeter of the gears as happens when the pump is rotating correctly and efficiently,
3. The exiting fluid departs through the Pump discharge in the usual way, then the fluid moves onwards into the AHC pipework in the usual way,
4. There will be unusual noise and vibration because the fluid is forced between the teeth as the fluid passes between the gears, also causing side pressure on the gears (which may be pushed into the chamber walls causing wear marks, also slightly tilt the gears causing scribing on the base of the gear chamber), and with side pressures on the gear-shafts and gear-cases as well,
5. Excessive pressure developed between the gear teeth would be relieved (with noise and vibration) by fluid passing via the “notch” where one gear-case joins the other, then the fluid passes through the clearances around the gear-shafts and gear-cases, then passes through the Bypass Strainer in the usual direction, then returns to the Inlet Strainer in the usual way -- in other words, more fluid recirculates than would be the case with the pump in reverse than occurs in correct rotation,
6. There will be sub-optimal flow and pressure developed by this reverse operation of the AHC Pump – but there will be adequate flow and pressure to perform as observed and described above,
7. The fluid flow does not and cannot flow backwards through the Strainers and does not provide any ‘back-washing’ effect,

So I am overthinking this -- or I am missing something basic here?

Can you please help me clear my mental fog??

 

[suprasvobodea]

WITH LATE EDITS ADDED:

Given the previous descriptions, there is no room for doubt that there is air in the AHC system -- which makes this the first cause of DTC C1762 to pursue as held all along by @suprarx7nut [but this is not the only cause, as shown by @BullElk (internal O-rings between the gear carriers and the top-plate of the pump sub-assembly) and others including me (Inlet Strainer just before the gears inside the pump) -- with many previous posts and pictures on this topic].

@suprarx7nut recommends clearing air from system by direct connection of the AHC Pump Motor to a 12 volt battery and running the air out through one or more bleeders.

[The intention to start the attempt with the bleeder at the Height Control Accumulator certainly is a very good idea -- once air-infected fluid is in the Height Control Accumulator, it is sent throughout the system and infects everything when the Height Control Accumulator next participates in raising the vehicle. Eventually, the air-infected fluid returns to the AHC Tank (except for the portion trapped in various places in the system) – and in the AHC Tank it may dissipate to atmosphere, or, the air-infected fluid may be sent through the system again!]

@2001LC also suggests just try the direct 12 volt connection and see what happens.

@Moridinbg reported at Post #251 at The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-13#post-14466838 that he had tried this and it did not work for him (as also noted in my previous post #34 in this this thread), and also describes in the subsequent post below some other experiences.

@IndroCruise (me) is sceptical for reasons given previously about whether direct 12 volt connection would work -- also sceptical that the solenoid valve on the Height Control Accumulator will open without the required signal from the ECU.

LATE EDITED NOTE 1: If there has been no bleed from a working bleeder at the Height Control Accumulator, then there is no fluid in there -- or possibly (but unlikely that the Height Control Accumulator is faulty)** -- meaning that it is much more likely that the AHC Pump HAS NOT re-charged the Height Control Accumulator.

**LATE EDITED NOTE 2: Note that Height Control Accumulators pre-November 2002 are the subject of the warning in Technical Services Bulletin Reference CP-3006 (attached) which specifically advises of breakdown of an O-ring within the Height Control Accumulator, leading to blockage of the Inlet Strainer inside the AHC Pump and which specifically nominates DTC C1762.

However, I would be VERY happy -- in fact delighted -- to be proved wrong on all and any of the above issues. It certainly would make clearing air and gas problems sooo much easier!!

If the Levelling Valves and/or the Height Control Accumulator Solenoid Valve (on Techstream: SLFL = SoLenoid Front Levelling; SLRL = SoLenoid Rear Levelling; (Left and Right are not distinguished on Techstream); and SLAC = SoLenoid ACcummulator) are preventing fluid discharge from the AHC Pump, then strange noises are entirely unsurprising from a churning positive displacement gear pump.

When the AHC Pump operates, as a Gear Pump it must force fluid to flow somewhere, or stop, or break -- like any other Gear Pump, large or small. Several DTC protections exist on the AHC Pump because, unlike industrial gear pumps, there is no pressure relief valve protecting the AHC Pump. Unlike some other kinds of pumps (such as a centrifugal pump) a Gear Pump requires actual movement of fluid and cannot simply churn in a liquid.

If the discharge is blocked or valves are closed downstream, the only fluid routes available to the AHC Pump are via the clearances around the gear cases and gear shafts inside the Pump, then through the Bypass Strainer and back to the Pump Inlet Strainer, probably with some cavitation along the way -- or maybe -- directly across the top and bottom planes of the gears and around the gear perimeter if there has been enough wear to provide sufficient clearances. Whatever, any of these are very high resistance paths and will be very noisy.

Just to be clear. This is not a competition. It is an international effort by different people volunteering their own time, experience and energies to help find a solution by exploring different ideas and opinions. Better advice will not be found elsewhere!

Suggested next steps:

1. [LATE EDIT]: A replacement Pressure Sensor is on the way -- suggest for self-satisfaction double check that it is correct Part Number for the vehicle VIN, then install after conducting the FSM test procedure to ensure that the test voltages are in the correct range of 1.48 volts to 1.85 volts. If this is successful in overcoming the current breakdown -- GREAT!! We all learn something. If not successful, then the following further steps are suggested:
2. Break the line at the AHC Pump discharge and/or after the Attenuator (below the Pump) and check for positive discharge from the AHC Pump with direct connection to the 12 volt battery,
3. Persist with multiple repetitions of clearing DTC C1762 and re-starting over and over again to see whether flow can be developed and vehicle height maintained,
4. Consider gel blockage of the Inlet Strainer inside the AHC Pump sub-assembly OR the kind of Inlet Strainer blockage advised in TSB CP-3006, if that is relevant to the Manufacture Date of the vehicle,
5. Further ideas will follow later ….. including discussion of ideas by @2001LC on harness and wiring issues -- enough for now at 9:06pm in Eastern Australia.

Frustrations by @suprasvobodea are understood and respected -- we have all been there during the 'learning process'!!

WITH LATE EDITS ADDED:

Given the previous descriptions, there is no room for doubt that there is air in the AHC system -- which makes this the first cause of DTC C1762 to pursue as held all along by @suprarx7nut [but this is not the only cause, as shown by @BullElk (internal O-rings between the gear carriers and the top-plate of the pump sub-assembly) and others including me (Inlet Strainer just before the gears inside the pump) -- with many previous posts and pictures on this topic].

@suprarx7nut recommends clearing air from system by direct connection of the AHC Pump Motor to a 12 volt battery and running the air out through one or more bleeders.

[The intention to start the attempt with the bleeder at the Height Control Accumulator certainly is a very good idea -- once air-infected fluid is in the Height Control Accumulator, it is sent throughout the system and infects everything when the Height Control Accumulator next participates in raising the vehicle. Eventually, the air-infected fluid returns to the AHC Tank (except for the portion trapped in various places in the system) – and in the AHC Tank it may dissipate to atmosphere, or, the air-infected fluid may be sent through the system again!]

@2001LC also suggests just try the direct 12 volt connection and see what happens.

@Moridinbg reported at Post #251 at The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-13#post-14466838 that he had tried this and it did not work for him (as also noted in my previous post #34 in this this thread), and also describes in the subsequent post below some other experiences.

@IndroCruise (me) is sceptical for reasons given previously about whether direct 12 volt connection would work -- also sceptical that the solenoid valve on the Height Control Accumulator will open without the required signal from the ECU.

LATE EDITED NOTE 1: If there has been no bleed from a working bleeder at the Height Control Accumulator, then there is no fluid in there -- or possibly (but unlikely that the Height Control Accumulator is faulty)** -- meaning that it is much more likely that the AHC Pump HAS NOT re-charged the Height Control Accumulator.

**LATE EDITED NOTE 2: Note that Height Control Accumulators pre-November 2002 are the subject of the warning in Technical Services Bulletin Reference CP-3006 (attached) which specifically advises of breakdown of an O-ring within the Height Control Accumulator, leading to blockage of the Inlet Strainer inside the AHC Pump and which specifically nominates DTC C1762.

However, I would be VERY happy -- in fact delighted -- to be proved wrong on all and any of the above issues. It certainly would make clearing air and gas problems sooo much easier!!

If the Levelling Valves and/or the Height Control Accumulator Solenoid Valve (on Techstream: SLFL = SoLenoid Front Levelling; SLRL = SoLenoid Rear Levelling; (Left and Right are not distinguished on Techstream); and SLAC = SoLenoid ACcummulator) are preventing fluid discharge from the AHC Pump, then strange noises are entirely unsurprising from a churning positive displacement gear pump.

When the AHC Pump operates, as a Gear Pump it must force fluid to flow somewhere, or stop, or break -- like any other Gear Pump, large or small. Several DTC protections exist on the AHC Pump because, unlike industrial gear pumps, there is no pressure relief valve protecting the AHC Pump. Unlike some other kinds of pumps (such as a centrifugal pump) a Gear Pump requires actual movement of fluid and cannot simply churn in a liquid.

If the discharge is blocked or valves are closed downstream, the only fluid routes available to the AHC Pump are via the clearances around the gear cases and gear shafts inside the Pump, then through the Bypass Strainer and back to the Pump Inlet Strainer, probably with some cavitation along the way -- or maybe -- directly across the top and bottom planes of the gears and around the gear perimeter if there has been enough wear to provide sufficient clearances. Whatever, any of these are very high resistance paths and will be very noisy.

Just to be clear. This is not a competition. It is an international effort by different people volunteering their own time, experience and energies to help find a solution by exploring different ideas and opinions. Better advice will not be found elsewhere!

Suggested next steps:

1. [LATE EDIT]: A replacement Pressure Sensor is on the way -- suggest for self-satisfaction double check that it is correct Part Number for the vehicle VIN, then install after conducting the FSM test procedure to ensure that the test voltages are in the correct range of 1.48 volts to 1.85 volts. What specifically do u mean “ Install the new SENSOR, AFTER conducting FSM test procedure ”. Don’t I have to install it in the pump , press the UP-DOWN switch after starting engine to get a Voltage reading..?? This is important… as I don’t want to mess up the sequence…& ruin something in this repair. Please REPLY , ASAP , as I need to know these details before beginning.

1. If this is successful in overcoming the current breakdown -- GREAT!! We all learn something. If not successful, then the following further steps are suggested:
2. Break the line at the AHC Pump discharge and/or after the Attenuator (below the Pump) and check for positive discharge from the AHC Pump with direct connection to the 12 volt battery,
3. Persist with multiple repetitions of clearing DTC C1762 and re-starting over and over again to see whether flow can be developed and vehicle height maintained,
4. Consider gel blockage of the Inlet Strainer inside the AHC Pump sub-assembly OR the kind of Inlet Strainer blockage advised in TSB CP-3006, if that is relevant to the Manufacture Date of the vehicle,
5. Further ideas will follow later ….. including discussion of ideas by @2001LC on harness and wiring issues -- enough for now at 9:06pm in Eastern Australia.

Frustrations by @suprasvobodea are understood and respected -- we have all been there during the 'learning process'!!

 

[suprasvobodea]

Indocruise

I responded to your question above in RED about the install of new PS & voltage reading … Need clarification on this procedure please .

 

[IndroCruise]

Question from @suprasvobodea:

What specifically do u mean “ Install the new SENSOR, AFTER conducting FSM test procedure ”. Don’t I have to install it in the pump , press the UP-DOWN switch after starting engine to get a Voltage reading..?? This is important… as I don’t want to mess up the sequence…& ruin something in this repair. Please REPLY , ASAP , as I need to know these details before beginning.

Answer from @IndroCruise:

Yes -- exactly that -- per last page of the FSM extract as attached -- just wanted to clarify. And apologies for confusion, the word "after" should not have appeared in my sentence, main point was for engine to be running, which you have now clarified.

 

[2001LC]

2001 LC

PLEASE SEE MY ANSWERS IN RED TO YOUR STATEMENTS/QUESTIONS ABOVE. What is IIRC ..?
Update after 2 hr of diagnostic fun :
I started doing the electrical troubleshooting per your suggestion
I disconnected the Accumulator 2-pin connector and checked impedance through all the intermediate connectors directly to the AHC ECU pin #24 (SLB) and pin 6 (SLAC) on the AHC ECU. I got 3 ohms on both leads from the connector back to the ECU so they are good! Also got 3 ohms on the 3 wires on the pressure switch connector back to the ECU. That is the only connector I touched besides the 3 pump connectors in the engine bay.
I think I found that gray connector in the DS rear axle on top of the frame, but it is even MORE inaccessible than the top of the strut that I cut a hole to access the top two 10 mm bolts and end cap! I too had to raise the rear with jack stands, as my LX is resting on the stops (and is as low as a Corvette now,). Please let me know if anyone can tell me HOW to access this large gray connector that rests on top of the frame rail on the driver's side I might try to disconnect it, but it may not be worth it. I don't think I need to go there, as the system DID WORK with a new PS after I installed it and I ran the reservoir to almost empty and heard that "noise " of an empty tank! and shut down the engine.
I cleared the 1762 code and as soon as I turned on the car and did the active test by pushing the DOWN switch, it immediately got 1762.

Im again past frustrated and ready to sell this damn thing. The electrical wire issue I tried ( between the Accumulator and ECU was good. ) I can't access the large gray connector on top of the frame on the Drives side rear wheel ( per 2001LC -body-off-frame pictures in post

The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-13#post-14465654

from 2001 LC is nice, but the truck's body is removed! Since my LX was working before I opened up the system and replaced everything, and I didn't touch anything electrical under the back rear vehicle ( just the midsection to remove the supply line from the accumulator to the pump attenuator by the PS frame- due to a rounded flare nut!!!! ).

If ANYONE reading this thread has any more specific ideas about specific connectors or impedance checks on specific wire harnesses per the TSM or your own experience, PLEASE let me know. I truly appreciate all the suggestions so far and have implemented them ( except for that large gray rear connector on top of the DS rear frame rail- as explained above)

All I can think of anymore ., is to wait till another new PS arrives, install it, fill the reservoir, start the LX with the ACTIVE TEST, and see if it will work again. I am truly at the end of my game here and don't know what to try to think to do anymore...... I wish one of you guys was close to Dallas TX. I would like to meet you first of all, and then tackle this problem, in the flesh until we beat it int submission.

BTW. Color fonts, are used when answering right next to a question in a quote. Sometime @IndroCruise showed me and uses very well.

Again all issues began after you serviced. So focus is first on what you touched, order of procedures and failures.

I do not thing electric fault your issue:

My bring electric fault back into the picture. Was a 2% chance, sometime just happen to happen (like rodent or moisture) while vehicle had been sitting for months. I brought back up for 2 reason. 1) you asked; how to test wires. 2) in the event DTC cleared and came back with IG key ON (without starting engine)

Since you were able to run pump, IG key on engine off. Without getting a DTC C1762, until engine running. This reduces the chance of a fault in wires from CPU to undercarriage wire harness on to accumulator, controller, globes and rear height sensor. I'm not saying you don't have a wire harness fault. Just that we've moved from 2%, to less than 2% chance. Because you ran pump from TS, engine off.

Just put the below info, on the back burner:

I understand correctly, you tested wires from accumulator to the CPU. That is end to end. Wire runs from CPU, along inside of body under thresholds to rear 1/4 in cabin driver side (DS). It then penetrates body DS rear 1/4 and comes out near bumper, where we can see multiple wire housing connection blocks. This is where undercarriage wire harness connect. Undercarriage wire harness connect to high sensor, controller and accumulator. So you can also test CPU to controller. While wire harness connection block off controller, test control also.

Those farme off picture, that show some gray wire connector blocks, aren't easily accessible. If we happen to isolate a wire, that passes through those. We just run a jumper wire bypassing it/them.

Laying on the ground behind DS rear mud flap, near rear bumper looking up.
Between DS rear body 1/4 tip and frame. Is where wire harness from cabin penetrate body and undercarriage wire harness connect. I've found two of the wire hosung block contain wire to AHC accumulator and controller.These wire are also for rear height sensor, globes, ABS trail lights etc.

This is the harness connected to accumulator, control, etc. That connect to the gray wire blocks hidden by body on top of frame.

 

[IndroCruise]

WITH LATE EDITS ADDED:

Given the previous descriptions, there is no room for doubt that there is air in the AHC system -- which makes this the first cause of DTC C1762 to pursue as held all along by @suprarx7nut [but this is not the only possible cause, other examples exist such as

• example by @BullElk (worn internal O-rings between the gear carriers and the top-plate of the pump sub-assembly),
• example by @IndroCruise and others (fully or partially blocked Inlet Strainer just before the gears inside the pump with many previous posts and pictures given on this topic),
• possible Pressure Sensor failure (extremely rare, not experienced by AHC professionals such as @suprarx7nut and @2001LC, not found by Search in IH8MUD100 series Forum,
• DTC C1762 also has been reported in parallel with other DTC's and conditions which were the root cause.

@suprarx7nut recommends clearing air from system by direct connection of the AHC Pump Motor to a 12 volt battery and running the air out through one or more bleeders.

[The intention to start the attempt with the bleeder at the Height Control Accumulator certainly is a very good idea -- once air-infected fluid is in the Height Control Accumulator, it is sent throughout the system and infects everything when the Height Control Accumulator next participates in raising the vehicle. Eventually, the air-infected fluid returns to the AHC Tank (except for the portion trapped in various places in the system) – and in the AHC Tank it may dissipate to atmosphere, or, the air-infected fluid may be sent through the system again!]

@2001LC also suggests just try the direct 12 volt connection and see what happens.

@Moridinbg reported at Post #251 at The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-13#post-14466838 that he had tried this and it did not work for him (as also noted in my previous post #34 in this this thread) -- with other experiences further described by @Moridinbg in his subsequent post #50, next below in this thread.

@IndroCruise (me) is sceptical for reasons given previously about whether direct 12 volt connection would work -- also sceptical that the solenoid valve on the Height Control Accumulator will open without the required signal from the ECU.

LATE EDITED NOTE 1: If there has been no bleed from a working bleeder at the Height Control Accumulator, then there is no fluid in the Height Control Accumulator -- or possibly (but unlikely) the Height Control Accumulator is faulty** -- meaning that it is much more likely that the AHC Pump HAS NOT re-charged the Height Control Accumulator.

**LATE EDITED NOTE 2: Note that Height Control Accumulators pre-November 2002 are the subject of the warning in Technical Services Bulletin Reference CP-3006 (attached) which specifically advises of breakdown of an O-ring within the Height Control Accumulator, leading to blockage of the Inlet Strainer inside the AHC Pump and which specifically nominates DTC C1762. However, the Height Control Accumulator was replaced with new OEM in 2023.

For all of that, I would be VERY happy -- in fact delighted -- to be proved wrong on all and any of the above issues. It certainly would make clearing air and gas problems sooo much easier!!

If the Levelling Valves and/or the Height Control Accumulator Solenoid Valve (on Techstream: SLFL = SoLenoid Front Levelling; SLRL = SoLenoid Rear Levelling; (Left and Right are not distinguished on Techstream); and SLAC = SoLenoid ACcummulator) are preventing fluid discharge from the AHC Pump, then strange noises are entirely unsurprising from a churning positive displacement gear pump.

When the AHC Pump operates, as a Gear Pump it must force fluid to flow somewhere, or stop, or break -- like any other Gear Pump, large or small. Several DTC protections exist on the AHC Pump because, unlike industrial gear pumps, there is no pressure relief valve protecting the AHC Pump. Unlike some other kinds of pumps (such as a centrifugal pump) a Gear Pump requires actual movement of fluid and cannot simply churn in an incompressible liquid.

If the discharge is blocked or valves are closed downstream, the only fluid routes available to the AHC Pump are via the clearances around the gear cases and gear shafts inside the Pump, then through the Bypass Strainer and back to the Pump Inlet Strainer, probably with some cavitation along the way -- or maybe -- directly across the top and bottom planes of the gears and around the gear perimeter if there has been enough wear to provide sufficient clearances. Whatever, any of these are very high resistance paths, pump performance will be poor and also very noisy.

Just to be clear. This is not a competition. It is an international effort by different people volunteering their own time, experience and energies to help find a solution by exploring different ideas and opinions. Better advice will not be found elsewhere!

Suggested next steps:

1. [LATE EDIT]: A replacement Pressure Sensor is on the way -- suggest for self-satisfaction double check that it is correct Part Number for the vehicle VIN, then install after conducting the FSM test procedure to ensure that the test voltages are in the correct range of 1.48 volts to 1.85 volts. If this is successful in overcoming the current breakdown -- GREAT!! We all learn something. If not successful, then the following further steps are suggested:
2. Break the line at the AHC Pump discharge and/or after the Attenuator (below the Pump) and check for positive discharge from the AHC Pump with direct connection to the 12 volt battery,
3. Persist with multiple repetitions of clearing DTC C1762 and re-starting over and over again to see whether flow can be developed and vehicle height maintained,
4. Consider gel blockage of the Inlet Strainer inside the AHC Pump sub-assembly OR the kind of Inlet Strainer blockage advised in TSB CP-3006, if that is relevant to the Manufacture Date of the Vehicle or the Height Control Sensor -- check the date code on the Accumulator with the information in TSB CP-3006,
5. Further ideas will follow later ….. including discussion of ideas by @2001LC on harness and wiring issues -- enough for now at 9:06pm in Eastern Australia.

Frustrations by @suprasvobodea are understood and respected -- we have all been there during the 'learning process'!!

Picking up the trail again ….

Vehicle Background and Symptoms:

Vehicle: 2002 – LX470,
Correspondent: @suprasvobodea
Location: Dallas, Texas, USA,
Fall 2023: Four new OEM ‘globes’ installed ex Impex,
Fall 2023: New OEM Height Control Accumulator installed ex Impex,
Jan 2024: Front ‘Shock Absorbers’ removed to replace bushes, then re-installed,
Jan 2024: Rear ‘Shock Absorbers’ removed to replace bushes, then re-installed,
Mar 2024: New OEM AHC Pump sub-assembly installed ex Impex

Persistent DTC C1762 arose and is continuing after finalising the above replacements and re-installations.

“Active Test” generally is not responding to either Techstream method nor manual method of shorting Ts & E1 at DLC1 along with correct operation of console switches.

It is possible (?) that Techstream was left connected at DLC3 when the manual method of “Active Test” was attempted at DLC1 -- in which case a conflict will prevent “Active Test” from working. “Active Test: should be attempted using manual method at DLC1 per attachment provided long ago by @PADDO, without Techstream connected at DLC3.

No other continuing DTC’s are reported.

The stance of vehicle is unclear -- except that the vehicle is in the “LO” height position or on the bump-stops and all attempts to raise the vehicle have been unsuccessful.

No information is given on

• Front cross-level of vehicle,
• Rake of the vehicle,
• Height Control Sensor readings from Techstream,
• Condition of Height Control Sensors,
• Corresponding physical hub-to-fender ‘ride heights’ measured by tape-measure, and,
• any indications of inconsistency of hub-to-fender measurements with conditions and readings of Height Control Sensors.

Note: Absence of DTC’s C1711, C1712 and C1713 DOES NOT indicate that the respective Height Control Sensors are healthy and working correctly or reliably.

Large differences in signal voltages from Height Control Sensors are one of the common causes of a “Fail Safe Mode” even without any DTC recorded -- but this is not the only possible cause. The other 8 (?) "Fail Safe Mode" possibilities -- all slightly different but all prohibiting AHC/TEMS operation -- can be explored in the AHC DIAGNOSTICS section of the FSM.

Elsewhere, DTC C1762 has been reported in parallel with DTC's C1711, C1712, C1713 and may have been the 'root cause' of some incidences of DTC C1762.

Subject to the views of others, the following revised sequence of next steps are suggested:

1. @suprasvobodea advises that a replacement Pressure Sensor is on the way. For his self-satisfaction, and whether or not Pressure Sensor failure is likely, it is suggest to conduct again the previously attached FSM test procedure per DTC C1762 and NOTES below, expecting results of 1.48 volts to 1.85 volts for the existing Pressure Sensor, OR, first double-check that Part Number 89192-60020 of the new Pressure Sensor is correct for the vehicle VIN, then install and test this new Pressure Sensor,
2. NOTES (i): Previous tests of old and replacement Pressure Sensors gave results of around 0.505 volts while the engine was operating but the AHC Pump was NOT OPERATING because operation was prohibited by ECU due to DTC C1762,
3. NOTES (ii): The FSM is unclear on the detail -- one of its shortcomings -- but higher voltages are expected when the engine AND the AHC Pump ARE OPERATING,
4. When the AHC Pump is not operating there is only atmospheric pressure within the AHC Tank and Pump through to the Control Valve Assembly and the contained Levelling Valves -- so higher pressures in the AHC Pump and in the lines and higher test voltages must be expected in the Pressure Sensor when the AHC Pump is operating,
   
   
5. NOTES (iii): At Post #31 of this thread, @suprasvobodea confirms correct voltages (around 5 volts) at relays and connections per FSM Test Procedure for DTC C1762 which indicates electrical good health that far in the system.
6. NOTES (iv): It is then noted that: “Then I tested the Pressure switch both at the connector at the pump and on the Connector at the AHC ECU by the steering wheel and they both were 0.505 V. That is why I say the issue is with the Pressure Sensor .... it's simply sending the wrong voltage to the ECU - thus the continuous fail-safe issue with the pump not working!” This conclusion is not correct. This is where the misunderstandings begin,
7. NOTES (v): The test voltage is low (and is expected to be correct) because the actual pump and line pressures are lower in this non-operating condition than they will be if the AHC Pump is operating – then the pressures and voltages could be expected to reach the FSM-specified voltages,
8. RE-TEST: Suggest connect AHC Pump to 12 volt supply for long enough to re-test Pressure Sensor voltages while AHC Pump is operating and developing pressure and compare with FSM-specified test voltages,
9. Determine then whether the Pressure Sensor is healthy or defective!!
10. If this is successful in overcoming the current AHC breakdown -- GREAT!! We all learn something. If not successful and DTC C1762 persists, then the following further steps are suggested:
11. Usinf a direct 12 volt connection to the AHC Pump Motor, confirm that the AHC Pump operation is unimpaired, by breaking the line at the AHC Pump discharge (or preferably after the Attenuator just below the Pump because the Attenuator has been reported by others as an air/gas trap) and check for a strong positive convincing discharge (not just a leak) from the AHC Pump (without any suspicion of blocked internal strainers), then,
12. If satisfied with AHC Pump operation, close the AHC system, then persist with multiple repetitions of clearing DTC C1762 and then re-starting over and over again, using the 0.6 seconds gap between each start/stop of the AHC Pump to see whether flow can be developed and vehicle height brought back to “N” to allow bleeding at all 5 bleeders, one-by-one starting at the Height Control Accumulator, and if unsuccessful,
13. Consider gel blockage of the Inlet Strainer inside the AHC Pump sub-assembly OR the kind of Inlet Strainer blockage advised in TSB CP-3006 (previously attached), if that is relevant to the Manufacture Date of the Height Control Accumulator -- check the date code on the new OEM Accumulator with the information in TSB CP-3006, and if the above ideas are unsuccessful or irrelevant,
14. Pursue the ideas suggested by the professionals, @2001LC and @suprarx7nut, in their Posts and links/references in reply to the two threads used by @suprasvobodea -- concerning harness, connector and wiring faults -- noting how these can be intermittent (and noting that IIRC means “If I Recall Correctly”), and including consideration of the following:
15. Consider all previously disrupted electrical connections, connectors and nearby portions of the harnesses, which were involved in removal and re-installation of the Height Control Accumulator, AHC Pump, each Front and Rear ‘Shock Absorber’ (a.k.a. strut) and each Damping Force Actuator to which each ‘globe’ is attached,
16. Inspect carefully all parts of the harness visible under the body (preferably with vehicle on a hoist and with a strong light), looking for possible areas of harness damage, especially near any part of the exhaust system, or where harness or connectors are exposed to damage from road debris thrown up while travelling, or where connectors have lost their protective cover and are exposed to water thrown up while travelling (such as at the Control Valve Assembly, all three Height Control Sensors, also the connectors behind the Rear Quarter panel -- especially the AHC junction "BI1" connector visible from below (NOT on top of the chassis rail) and shown on Electrical Wiring Diagrams (EWD) as “BI1” (BRAVO INDIA ONE - all upper case, not Bi1 which is elsewhere),
17. Junction BI1 is a useful test point when looking for causes AHC issues,
18. In the relevant places, test for voltages using the voltage values in the table “Terminals of ECU” in the AHC “DIAGNOSTIC” pages in the FSM,
19. Also test for continuity from one connector to the next available in line in the suspected harness areas. The “Electrical Wiring Routing” pages in the FSM which show where all connectors are located.
20. There will be a solution to the issues on this vehicle -- unlikely to be expensive but likely to require persistence.

 

[2001LC]

Good writeup, as always @IndroCruise.

One thing that been making it difficult to help him. Is his painting with a broad bush, then remembering giving detail after I've draw conclusion and written a response based on statements made. One very important point is, when did failsafe C1762 first accrue. Which I may have wrong. But I have after, shock reinstalled possible after pump R&R. If earlier, say pre globes or after accumulator. This would change where I'd first look.

______________________________________________
"
Vehicle Background and Symptoms:

Vehicle: 2002 – LX470,
Correspondent: @suprasvobodea
Location: Dallas, Texas, USA,
Fall 2023: Four new OEM ‘globes’ installed ex Impex,
Fall 2023: New OEM Height Control Accumulator installed ex Impex,
Jan 2024: Front ‘Shock Absorbers’ removed to replace bushes, then re-installed,
Jan 2024: Rear ‘Shock Absorbers’ removed to replace bushes, then re-installed,
>>>?? Failsafe C1762
Mar 2024: New OEM AHC Pump sub-assembly installed ex Impex
>>>?? Failsafe C1762
"
___________________________________________

Wasn't it after shock install, when first C1762 kick in failsafe. At first, no mention of pre flushing and bleeding of shocks. He then came back and said he did. With, little detail as to how.

Let assume a mistake made, where shock still had some air internal/deep in them. Then in raising LCA with shock attached, so to attach shocks top nut. Shock compressed a bit, and then top nut attached. He in then topped off shock and attached HP fitting. Then removing jack allowing LCA to fully extend shock after HP fitting attached. Any extension of shock, would have drawn in some air from HP line. HP lines to globes, were likely empty of most fluid at this point. He then lowers vehicle, with all bleeders closed. Compressing air, rather than leaving a pathway for escape (open bleeders).

The picture gets foggery, as to how much fluid in reservoir and at what points. Hearing what he thought empty reservoir. Was it empty???. If he had filled to the with 1" top, from a full 2.5L tin, empting tin into reservoir. It can't have emptied, with all good globes, accumulator and shocks pre filled. Unless it was running out of a leak, which he should have seen leak.

Also his 20 second N to H. Very likely due to T-bar out of adjustment, not carrying enough weight.

Conclusion:

Air in AHC shocks and lines, plus carrying to much weight on shocks.

 

[suprasvobodea]

1. RE-TEST: Suggest connect AHC Pump to 12 volt supply for long enough to re-test Pressure Sensor voltages while AHC Pump is operating and developing pressure and compare with FSM-specified test voltages,
   

   Good writeup, as always @IndroCruise.
   
   One thing that been making it difficult to help him. Is his painting with a broad bush, then remembering giving detail after I've draw conclusion and written a response based on statements made. One very important point is, when did failsafe C1762 first accrue. Which I may have wrong. But I have after, shock reinstalled possible after pump R&R. If earlier, say pre globes or after accumulator. This would change where I'd first look.
   
   ______________________________________________
   "
   Vehicle Background and Symptoms:
   
   Vehicle: 2002 – LX470,
   Correspondent: @suprasvobodea
   Location: Dallas, Texas, USA,
   Fall 2023: Four new OEM ‘globes’ installed ex Impex,
   Fall 2023: New OEM Height Control Accumulator installed ex Impex,
   Jan 2024: Front ‘Shock Absorbers’ removed to replace bushes, then re-installed,
   Jan 2024: Rear ‘Shock Absorbers’ removed to replace bushes, then re-installed,
   >>>?? Failsafe C1762
   Mar 2024: New OEM AHC Pump sub-assembly installed ex Impex
   >>>?? Failsafe C1762
   "
   ___________________________________________
   
   Wasn't it was after shock install, when first C1762 kick in failsafe. At first, no mention of pre flushing and bleeding of shocks. He then came back and said he did. With little detail as to how.
   
   Let assume a mistake made, where shock still had some air internal/deep in them. Then in raising LCA with shock attached, so to attach shocks top nut. Shock compressed a bit, and then top nut attached. He in then topped off shock and attached HP fitting. Then removing jack allowing LCA to fully extend shock after HP fitting attached. Any extension of shock, would have drawn in some air from HP line. HP lines to globes, were likely empty of most fluid at this point. He then lowers vehicle, with all bleeders closed. Compressing air, rather than leaving a pathway for escape (open bleeders).
   
   The picture gets foggery, as to how much fluid in reservoir and at what points. Hearing what he thought empty reservoir. Was it empty???. If he had filled to the with 1" top, from a full 2.5L tin, empting tin into reservoir. It can't have emptied, with all good globes, accumulator and shocks pre filled. Unless it was running out of a leak, which he should have seen leak.
   
   Also his 20 second N to H. Very likely due to T-bar out of adjustment, not carrying enough weight.
   
   Conclusion:
   
   Air in AHC shocks and lines, plus carrying to much weight on shocks.

You may be correct SInce i filled the shocks, after attaching the lower bolts and lifting the LCA with a small jack to compress the actuator until fluid overflowed and tightened the top cap. This might have drawn any air back into the shock when I lowered the LCA from the lines running to it. ! But this should NOT cause the ACTIV TEST to not run... should it ..? I mean that's WHY there is a manual test like this ..... to force fluid into the accumulator >> shocks to remove it