AHC (1 Viewer)

[HarperKE]

Hi guys, I just got an LX470. the previous owner had removed the original height control shocks and installed stiff gas shocks. Everything else related to this system is intact so i bought a set of OEM shocks and have installed them. The problem is now the pump cuts off when i try to raise the car and the error code shows insufficient pressure on the pressure sensor. What am i missing??

 

[BullElk]

You bought OEM AHC "shocks" ?

 

[HarperKE]

Yes genuine shocks from the dealer.

 

[BullElk]

Smarter than I will chime in.

 

[Surfy]

AHC is a oil based suspension system. My mechanic says it is not so easy to do maintenance.

Did you fill in AHC Liquid and did follow the work instructions?

 

[HarperKE]

I have owned 2 cars before this and I have followed all the instructions. I own a garage so know my way about mechanicals. Used the original fluid....

 

[utflowerman]

.

 

[HarperKE]

I have checked almost everything... Changing the pressure sensor too.

 

[Shortpencils]

My first guess would be air in the system still.

 

[dbfw]

I've only done basic maintenance on my AHC system, but have read through lots of threads on it and my FSM. I think the consensus is going to be "you need to bleed the air out of the system." I'm sure this will go hand in hand with verifying that all lines are connected properly and not leaking, then followed by some cycles of fill with fluid, attempt to raise to N, bleed, repeat.

Edit: I recall a thread a couple months ago where someone struggled to get their system re-primed just from leaving the bleeder valve open too long during a fluid flush. With all of your lines full of air, I'm sure it's going to take quite a bit of bleeding to chase it all out. Maybe someone with more knowledge of the system than me can chime in as to whether trying to pull a vacuum from any of the bleeders is possible. I'm not sure that it is if the right valves aren't open, etc.

 

[BullElk]

I suggest retrieve fluid from reservoir and bleed entire system. If that fluid isn’t real good, replace with new fluid and bleed until a bit of new fluid comes out then top off reservoir. Then try the AHC as it was meant to be used.

If your experience suggests a solution please pass it on to us fellow mudders.

 

[HarperKE]

I'm thinking the same but how to bleed it out... Everytime I set the code kicks in and that's it

 

[dbfw]

I seem to recall some way to force the pump to run without being commanded by the AHC ECU. Might be as simple as just putting +12V to it, but I'd wait for the resident AHC experts to confirm that before risking any damage to it. I'm not sure what the duty cycle is, but I know it can overheat if run too long continuously.

Found that thread I was thinking of. Lots of good discussion of bleeding techniques here. The problem turned out to be air in the system: AHC Inop after fluid change 2007 lx C1751 and C1762 - https://forum.ih8mud.com/threads/ahc-inop-after-fluid-change-2007-lx-c1751-and-c1762.1233088/

 

[ramangain]

What is the current state of the rig? Is it sitting on the bump stops because you've drained the old fluid, or have you not gotten to that step yet?

 

[dbfw]

What is the current state of the rig? Is it sitting on the bump stops because you've drained the old fluid, or have you not gotten to that step yet?

Good point, when the conversion to standard suspension was done, were the TBs and rear coils replaced as well with beefier parts? If so, there might not be enough weight on the hydraulics to properly force it down to do the bleed. OP, when you switched back to AHC shocks, did you also confirm you have AHC TBs and coils? They're softer than the standard LC versions.

 

[HarperKE]

Is there a way to "cheat" the AHC ECU that the pressure sensor is ok and working? Coz this would then run the pump long enough to push the fluid thru... The problem with directly running the pump is the solenoid block under the chassis won't open to let fluid flow.

 

[ramangain]

Did you say you changed the pressure sensor and the error code still remains?

 

[HarperKE]

Yes I did and same code still...

 

[HarperKE]

Good point, when the conversion to standard suspension was done, were the TBs and rear coils replaced as well with beefier parts? If so, there might not be enough weight on the hydraulics to properly force it down to do the bleed. OP, when you switched back to AHC shocks, did you also confirm you have AHC TBs and coils? They're softer than the standard LC versions.

It has the original coils and TBs... Only heavy duty shocks were installed. The car is now sitting low on the bump stops

 

[LXKevin]

Do you have Techstream?