AHC won't raise to High

[Toyo72]

I did a thorough search of the forums and couldn't find this specific problem, so here goes.
I'm looking at an '07 LX, a little over 100k miles. All seemed good, the vehicle is really clean and appears to have been well kept. The only issue I found was I couldn't get the AHC to raise to H. It would go from N to L, and would raise once the car hit ~20mph. Tried everything and it wouldn't raise to H to no avail.
Fluid would raise about 5 gradations between L and N. It also looked like one shock had been seeping fluid, as the lower tube was oily.
Likely a sensor, or could it be other things as well, including the shock? Pass on this one and keep looking?

 

[TXLX100]

Could be low fluid, weak pump, weak rear coils & torsion bars need adjustment. My 98 started doing that with a trailer on. New coils fixed it.

 

[Toyo72]

Thanks. Hadn't thought about the pump potentially being weak, I assumed it was likely ok as it did raise from L to N. Fluid level looked good, although it did look dirty.

 

[TXLX100]

Thanks. Hadn't thought about the pump potentially being weak, I assumed it was likely ok as it did raise from L to N. Fluid level looked good, although it did look dirty.

It could potentially be a bad sensor, but they usually act wonky when a sensor goes out. It requires more pressure to raise the vehicle from low to neutral, than neutral to high. If HIGH is selected and it tries to go to high, but cannot... The system doesn't have enough pressure to raise the vehicle (due to the pump, fluid, weak coils/TBs, etc). It probably has a DT code stored for "abnormal pressure" if that is the case.

If it's otherwise a good car, have the seller fix it contingent upon the sale, in my opinion.

 

[Wilsil]

Get a mini-VCI with techstream and see what your pressures are.

 

[Toyo72]

I don't have a mini-VCI (yet) so likely not enough time to get one and then go to inspect the car, and assuming that he would let me connect it.
I'll probably pass on the car, unless the seller comes back with an offer a couple grand lower than original asking price, then it might be worth taking the chance.

 

[Toyo72]

update - Lexus service reports that this one had separate repairs of one front and one rear leaking shock as well as front and rear height sensors between 20-40k miles. Of course this may or may not have any relevance to the current problem, but it is interesting that leaky shocks and failed sensors occurred in less than 40k miles. Not in a salty road area, either.

 

[PADDO]

update - Lexus service reports that this one had separate repairs of one front and one rear leaking shock as well as front and rear height sensors between 20-40k miles. Of course this may or may not have any relevance to the current problem, but it is interesting that leaky shocks and failed sensors occurred in less than 40k miles. Not in a salty road area, either.

It would seem this vehicle has an unflattering AHC history. To experience failed front and rear height sensors, combined with failed shock actuators under 40k miles makes it an outlier. Rear height sensors received improved environmental sealing via TSB in 2005 iirc, the front sensor design remains unchanged to the best of my knowledge. The shock actuators are a robust design that should provide many years and miles of leak free service. Two things that will cause premature failure leakage of the shock actuators are running at too high neutral pressure for too long and contamination, either chemical (wrong fluid used in the system) or particulate contamination due to poor hydraulic hygiene, swarf in the system or the like. The sensors, though part of the "system" are just rheostats and are independent to the hydraulics. There isn't a common link between the two that would cause early life failure in a vehicle used and maintained iaw the manufacturers intent. When I read your OP I thought "yeah, another under maintained system that has too high neutral pressures, should be pretty straight forward fix". But that history is a bit concerning, particularly the leakage. If these repairs were done under warranty it wouldn't be unheard off for a dealer to throw as many parts as Corporate, Region or whomever would pay for so the repair history could be skewed, but, coming from an AHC fanboy I'd proceed with caution. Could be that the original vehicle had some AHC hiccups that were corrected and now it has a simple over pressure problem that can be fixed with TB adjustment and new coils - or maybe not. Comes down to your appetite for risk and reward. Good luck.

 

[Toyo72]

Thanks PADDO. I thought this was odd history. The LX is otherwise very clean, interior is near perfect, but the service history at Lexus, doesn't show routine things like oil changes, so most maintenance must have been done elsewhere. Unless the price comes down substantially ($3k... at least), I'll pass.

I also forgot to mention that it was sold at around 45k miles as a Certified car by Lexus, even after all the AHC issues.

 

[scrappyslexus]

My truck had the AHC fluid contaminated by the dealer. It had all types of issues with the system not raising or lowering and bouncing. The dealer changed all the height sensors 5 plus times I lost count. They changed 1 or 2 shocks. It was only after reading about the pressures and the globes on this site that I realized dealer did not know anything about the system.

When I mentioned to the dealer how the system worked and what was occurring they decided to bring a lexus regional guy in. He found all the globes to be bad. Recommended changing the entire system. Over 10 k.

What I did was change all the globes. Had to call 6 lexus dealers, 5 dealers never heard or did the job. The one dealer had done it and got the job. Globes lasted from 75k to 133k. At 133k truck is bouncing changed fronts. the lexus shop I used is good but had no clue on system or the required pressures. They brought lexus engineer in and trained few senior techs on doing the globe change.

Some folks say globes should last a long time. I live in northeast bad roads, hilly and a lot of pot holes. I look at globes as shocks tha that néed changing.

Read all u can on Ahc system on this board and try to get it checked out.

Forgot to mention. Only one bad sensor from 75k to 133 k. About $300 at dealer. Kept old sensor and opened it up it the springs inside where corroded, probably road salt.

I hope all this helps.

 

[Toyo72]

Thanks @scrappyslexus - and I agree, this forum is invaluable with the knowledge base and so many people willing to help.

I have a feeling that may be what happened, at some point the fluid was contaminated, maybe the dealer doomed it from the start. I'm going to pass on this one, as he isn't coming down enough in price (it was priced reasonably well to begin with) to make it worth the risk and the hassle. Its a shame too, as the interior was absolutely perfect, no leather cracks or marked up door panels, and only one repaired scratch on the exterior.

Found another one I'm looking at that has all service documented routinely through Lexus, for more money of course.