AHC C1751 & C1762 Help/Recommendations/Suggestions (15 Viewers)

[beachbumin]

Hit me up again if I can be any help. With it getting a little cooler I've been back into my AHC on mine too. Good luck!

 

[NC-Grayson]

Hit me up again if I can be any help. With it getting a little cooler I've been back into my AHC on mine too. Good luck!

Thanks! I could use some help if you want to get together!!

 

[NC-Grayson]

just an update. did some very thorough investigating over the past week. Replacement ECU checks out, Relays check out, signals check out...everything checks out.

Ordered a pump sub-assembly and other small gaskets and such.....this is my last resort before ripping it all out

 

[NC-Grayson]

update for any following / future searchers:

The pump sub-assembly and related gaskets/o-rings solved my problem!

I think that makes me ~ 5th, (at least documented...in the world????), who have successfully solved a C1762 by replacing the pump sub-assembly.

For the record, following the FSM diagnostics regarding C1762, I had positive results out of EVERY test in the diagnostics except for the stage that involved the active test. This step simply said to perform the active test. This is the one test out of the five involved with diagnosing a C1762 that did NOT offer an "OK continue" or "NG" (no good) after performing the test.

The resivoir had fluid. The pump had power. The active test did NOT produce any activity. The pump relay checked out. The fluid pressure sensor checked out.

The pump sub-assembly was the key to all my woes.

I am so thankful for this community and the world-wide community that is Toyota.

 

[beachbumin]

Congrats Grayson! North End passes go on sale tomorrow through the 15th for half price

 

[NC-Grayson]

Congrats Grayson! North End passes go on sale tomorrow through the 15th for half price

Thanks Brad! How quickly I'd forgotten!

 

[suprasvobodea]

@YvesNL thanks for all your help, as well as @PADDO

I managed to get through all of the topics you described, and I'm still at a roadblock unfortunately.

Got my step values back to 8 somehow, (not sure what I did, but they're there at 8).

I still CANNOT get the system to "bleed air of AHC & AVS hydraulics system" or step 3 on the C1762 page in the FSM.

I can get the truck's AHC light to flash after pressing down 5x on the switch w/in 5 seconds of turning the key to on, but the truck will NOT raise.

it says, "Hint, at this time the AHC motor relay comes ON in order to raise vehicle height of the front wheels and air inside the AHC/AVS hydraulic system start to bleed with the pump motor operating"

HOWEVER, NONE OF THIS HAPPENS. It's like the ECU is not sending a signal to the motor relay to turn the pump on, because when I do the steps, the pump does not turn on!

12V power direct to pump - pump pumps
jumping AHC relay - pump pumps
bleed air of AHC/AVS hydraulic system - pump DOES NOT TURN ON, pump does not pump!

I'm so lost.

NC-Grayson

It's no coincidence I was steered to you and this thread..... because,............I HAVE THE EXACT SAME PROBLEM AS YOU DO. I CANNOT get the system to "bleed air of AHC & AVS hydraulics system" or step 3 on the C1762 page in the FSM.
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 whoever sees this maybe can help me solve this very puzzling situation I have now replaced 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

This is what i have AFTER replacing the Accumulator, and reinstalling the "shocks". NO PRESSURE!
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. BTW>> 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 time and $$$ if I had 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 12V directly for 30 sec, 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 bleed 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. (It 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!

 

[CrystallineMonk]

NC-Grayson

It's no coincidence I was steered to you and this thread..... because,............I HAVE THE EXACT SAME PROBLEM AS YOU DO. I CANNOT get the system to "bleed air of AHC & AVS hydraulics system" or step 3 on the C1762 page in the FSM.
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 whoever sees this maybe can help me solve this very puzzling situation I have now replaced 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

This is what i have AFTER replacing the Accumulator, and reinstalling the "shocks". NO PRESSURE!
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. BTW>> 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 time and $$$ if I had 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 12V directly for 30 sec, 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 bleed 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. (It 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!

I am dealing with the exact same problem and after reading this thread im leaning towards a pump sub assembly replacement with related gaskets and Orings. I am too far in to give up, though I looked at Ironman suspension kits this afternoon in my frustration.

 

[suprasvobodea]

I am dealing with the exact same problem and after reading this thread im leaning towards a pump sub assembly replacement with related gaskets and Orings. I am too far in to give up, though I looked at Ironman suspension kits this afternoon in my frustration.

Crystal Monk

I think your correct in your diagnosis… especially if you have exactly similar issues with your system.
I have a new pump subassembly on order from IMPEX. Waiting till Feb 29 . Before arrives from Japan to test out .
I’ll reply & post the details about Accumulator removal for anyone with seared bleeder valves after getting new pump installed in March

BTW …. STAY , STICK WITH YOUR AHC LEXUS HYDRAULIC SYSTEM. It’s far to great to trash it .& use a conventional one

 

[IndroCruise]

This link leads to a relevant post -- it is a long read but it covers some of your issues, especially under the sub-headings "What to do next?" and "Some notes on so-called ‘over-riding’ of the “fail safe functions”:

AHC Inop after fluid change 2007 lx C1751 and C1762

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...

forum.ih8mud.com

Good information here on pump removal -- not difficult.

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

 

[CrystallineMonk]

Crystal Monk

I think your correct in your diagnosis… especially if you have exactly similar issues with your system.
I have a new pump subassembly on order from IMPEX. Waiting till Feb 29 . Before arrives from Japan to test out .
I’ll reply & post the details about Accumulator removal for anyone with seared bleeder valves after getting new pump installed in March

BTW …. STAY , STICK WITH YOUR AHC LEXUS HYDRAULIC SYSTEM. It’s far to great to trash it .& use a conventional one

so I got my sub pump assembly today from IMPEX after a prolonged wait, referred to the link that IndroCruise posted above and dove in on the replacement... took me an hour start to finish. Lo and Behold it worked! my AHC is back in great working order....I am so super thankful for the information You (Suprasvobodea) and so many others have shared with everyone on this Forum... Long Live ih8Mud !!!

I am beside myself with joy and gratitude.

 

[suprasvobodea]

I am HAPPY and grateful to hear that you had success with your AHC with a new pump assembly!. I was expecting the same joyous revelation however my pressure switch on that pump gave a read out of .505 V which is way out of spec so I think that is still contributing to the inoperativeness of my system.
I had to place ANOTHER order for that very expensive pressure switch from IMPEX in Japan and I’m waiting its delivery.
Hopefully that will be the final solution to my problem and I can join you in joyous celebration and fulfillment.

 

[NicaLX470]

Bought a 2000 LX470 late 2021 with shown mileage of 130K (possibly rolled back?). Garaged it for six months, and then around mid 2022 started doing baseline maint and addressing any key issues. Main was the horrible ride quality. Replaced all globes and did a system flush (with fluid from the "dreaded" black bottles of that timeframe). Added 30mm spacers to top of rear coils (which helped bring down rear pressures to ideal reading).

Three years and 15K miles later, received 1751 and 1762 codes, with a drop to L position (no height change allowed, so stuck in L). Pump was showing some weird behavior (often moving, a bit louder than normal, etc.), but I just ignored. This problem had to addressed.

Drained fluid (black) and noted particles - especially from the driver's side mid-mount Accumulator Control Pump (49130-60010). Refilled with new fluid (from 2.5L can) expecting a miracle, but no fix. Then pulled the AHC pump/motor assembly off and replaced the pump sub-assembly. I was expecting to find a jelly mess inside the original pump, but luckily other than a small bit of dark crud inside the three-bolt end cap, no signs of any jelly. NOTE: my Accumulator Control Pump is original - with a production date code prior to the Oct 25, 2002 - which Toyota recommends changing if you ever see a DTC 1762. This has been ordered and I will replace when received. Fingers-crossed that system holds until then. Update to follow.