Possible AHC Height Control Accumulator Failure

[Zer0zg]

Hey guys,

First, I wanted to say I've been lurking this forum for a few months as I searched for my LX and you all seem extremely knowledgeable and helpful. I'm excited to join the community. Now onto my problem...

I recently purchased my first 100, an 04 LX with 180k miles. I got a great deal on it because of an AHC issue, and I'm pretty handy so I figured I could take it on(with your help) or in the worst case LC swap it. My use will be heavily street biased, so if I can reasonably keep the AHC I'd like to. I've done some searching, but this seems like a relatively uncommon failure mode, so I wanted some expert opinions.

When the dealership posted the ad for it, it stated that the truck was stuck in N with the light displaying OFF (i believe flashing). By the time I got the car, the car was stuck in L with OFF flashing. If you press raise, it flashes N for a bit then stops. So basically sounds like it's in fail safe mode.

My understanding is that this is often a sensor or a sensor/signal wire issue, however when I pull up the service history, it seems that this was diagnosed as a Height Control Accumulator Failure by a Lexus dealer 15k miles ago, and the repair was declined. I have not yet acquired a Techstream to pull down the errors. Looking at the forum, this doesn't appear to be all that common, so before I go down that road I wanted to see how likely this is to be the cause of failure, or whether it might be the dealer looking for a more expensive repair that fixing a corroded connector.

I just picked up the car(I'm not actually home yet), so I haven't had a chance to really get under it to dig around, but I wanted to get some advice so I know where to start. Thanks in advance!

 

[ArnieC]

Get Techstream running and see what codes it has and go from there. Could be 100 things but without the codes and data screens it would be a guess. AHC parts are expensive so it pays to diagnose properly.

 

[PADDO]

You’re correct in that the system has gone into a failsafe mode, based on the description. I’ve somewhere betwen zero and very little confidence in any dealer related AHC/AVS diagnosis - no fault codes or investigative description was entered by the dealer so my guess is that they guessed. Obviously can’t rule out a failed height accumulator via the interwebs but it’s the earlier model years that had potential issues, not 04s. You can manually check for DTCs and clear codes whilst waiting for Techstream, or a suitable code reader, but you should do a quick check of reservoir fluid level, loose connectors, broken harness, fuses too. Pretty much every solenoid or component test that can be done in Techstream can also be achieved manually fwiw.

 

[FxFormat]

If the truck is from New York, it's a rust bucket, and one thing that likes to break is the sensor linkage rod. Like this

It could also be a whole lot of other issue, blown shocks, bad pump, blown lines...check the fluid level in the reservoir and signs of leaks, inspect all the sensors, there's 2 in the front and one in there rear right infront of the spare tire.

 

[Zer0zg]

Thanks for the help guys, once it stops raining I’ll spend some time digging around under the car. The techstream is on the way, so once I have the codes hopefully they’ll help narrow it down.

And yeah, the car appears to have spent most of its life in Princeton NJ, but from what I’ve seen rust doesn’t look too bad, though I haven’t removed any bolts yet. I come from a 70’s Datsun background, so this thing is immaculate on my scale.

 

[Zer0zg]

Alright. So, I spent some time under the car and got the Techstream hooked up today. All of the sensors and linkages looked good, and I'm getting the C1762 low pressure for pump code. Took a closer look at the pump/reservoir and what I thought was the fluid level turned out to be dirty residue of fluid stuck to the sides of the tank, and the reservoir is basically empty. I didn't see any obvious leaks at the shocks or globes, but the car has been sitting /driven in the rain, so that may not be conclusive. The height control accumulator wires were a little wet with something, and the whole assembly was a bit rusty, but the accumulator itself felt dry. Plan is to refill the reservoir, give it some exercise and see if I can nail down the leak.

 

[Zer0zg]

Holy s*** it actually works! Filled up the fluid and the car actually lifts and drives amazingly smooth.

Drove it around for a mile or two and pulled over again to check for leaks. Sure enough, it appears to be coming from a gnarly looking hose that feeds the passenger side rear shock. Main worry now is getting the rusty old piece off...

Also checked my pressures and they look a bit high, though I do have my jack and toolbox in the rear. I'll plan on new rear springs and cranking the TB's pretty soon.

 

[Zer0zg]

Ordered both rear lines(driver's side isn't leaking, but is similarly rusty) and some more fluid. I have to say, I'm dreading getting to those shock bolts and stripping/breaking them. Any tips or tricks there?

 

[MongooseGA]

Yes. Get a flex head or even a double-flex head wrench for the upper rear shock bolts. And with the fluid line on the top of it, you might even consider the cargo-area-access-hole mod. If you do the latter, you don't really need the former. That's a personal preference kind of thing, though.

 

[Zer0zg]

Yeah, I just ordered a flex head 6 point for this. I'm not morally opposed to cutting a hole, but I'd like to avoid it if I can. Hopefully that works, if not I'll bust out the hole saw.

I'm excited, I've only driven this thing carefully on the bumpstops until now. The ride is amazing!

 

[MongooseGA]

Yeah, I just ordered a flex head 6 point for this. I'm not morally opposed to cutting a hole, but I'd like to avoid it if I can. Hopefully that works, if not I'll bust out the hole saw.

I'm excited, I've only driven this thing carefully on the bumpstops until now. The ride is amazing!

I don't blame you. On my last suspension install (non-AHC truck) I had relegated myself before the install day to cutting the hole. Luckily I had some extra hands that were more patient/smarter than I and it worked out fine.

The AHC is a fantastic system when it works. I was a little sad to remove it in favor of the foam cells I have in my LX now. Everything worked so well that I kept the big parts should they be useful to someone in the future. Congrats on getting it literally 'back up' again. Hopefully this will be an easy fix for you to enjoy it for many more miles.

 

[ArnieC]

Sure beats buying a line instead of an accumulator!

My coworker was following me out of work the other day - we have a lot of speed bumps in our parking lot. He has a new F150 and crawls over them. He was pretty amazed that I just drive over them at a moderate rate. Gotta love the AHC!

 

[Zer0zg]

Yeah for sure! Looking at my pressures it looks like new springs are in order. Is there a cost effective option out there for new LX springs other than direct from Lexus?

 

[trdcorolla]

You won't really know the current pressures until your system is working properly and hub to fender height is set. Just an FYI, I replaced my rear springs first, but the pressures went down a little but not much. I then added a 30MM spacer that got me in spec (I had to unplug the temp sensor, per the FSM, to get my reading, some don't). A lot of people say springs get tired/saggy so I didn't mind replacing them, made me feel better since I knew I would add sliders/roof rack in the future after I was done baselining it. When I placed an order for LX OEM springs I was told they were discontinued, so I had them order me 06/07 LC AHC rear springs. One spring is taller than the other, so if you replace them, make sure it's on the correct side.

 

[Zer0zg]

Gotcha, is setting the hub to fender height a matter of adjusting the sensors so that 0 on techstream matches an externally measured value, or something done through techstream? I can't seem to find definitive info.

 

[trdcorolla]

Yup, use the sensor to adjust the height. Once your hub to fender is set, use the torsion bars to adjust the pressure. Do this on level ground, with a typical load in the car (without you in it).

 

[Zer0zg]

Awesome, next order of business after I get the lines replaced and do a flush. Thanks again!

 

[FxFormat]

FYI i did my left front AHC line and it was an absolute nightmare, working with rust and trying to get the line out was horrible. I hope the rear is easier for you, but i doubt it. Good luck.

 

[MongooseGA]

Yup, use the sensor to adjust the height. Once your hub to fender is set, use the torsion bars to adjust the pressure. Do this on level ground, with a typical load in the car (without you in it).

I'm glad you mentioned load when adjusting T bars. When I was doing adjustments on my last AHC truck I cranked the bars with the truck on the ground, not knowing any differently. For adjusting the bars with a non-AHC vehicle, the recommendation is to lift the front end from the ground. This is more for my own clarification/curiosity than anything else but are they really supposed to be adjusted with standard load/on the ground?

 

[trdcorolla]

I think you can adjust the TB's anyway you want. I think lifted up or AHC on High will just make turning the bolt easier. The adjustment on level ground I was talking about was more for setting the height and checking the pressures.