01 LX470 AHC Suspension Issues (1 Viewer)

[lawdlc]

Apologies in advance for a long post but I want to get all the facts out there for consideration. First, I have searched and read so many threads on AHC suspension issues and sadly I left nearly more confused than I started. My 01 LX470 has 214,000 on the clock... I am second owner...first owner (before 120,000 miles) replaced some but not all of the accumulators. (I cannot find any records to determine which were replaced).

My truck has the classic SUPER BOUNCY rear end....its not bad driving on smooth roads, or over minor bumps, but undulating road surfaces cause the almost uncontrollable rear end bounce. My system seems to be otherwise working. It lifts to HIGH and drops to LOW when the button is pushed. It returns to N after reaching speed from either H or L setting. Fluid level seems to be appropriate and best I can tell I have not and am not losing fluid.

I removed and opened the rear height sensor hoping and praying that might be the issue...no such luck...zero corrosion, no evidence of any damage or corrosion whatsoever but lightly blew out the interior and reassembled/installed. No change.

I decided last week to schedule an appointment with my local Toyota dealer (Bill Penney Toyota Huntsville Alabama) and one of the largest T dealers in the state. Dropped my truck this morning with very clear instructions that I wanted to pay for AHC suspension diagnostics to determine what was causing the super bouncy rear ride. The service rep didn't exactly give me a warm and fuzzy when I checked in, but I figured hey what the hell. A few hours later I got the call back, service rep says...Oh yeah, Your rear shocks are blown. Need to be replaced. To which I asked How did you arrive at that conclusion. He talked in circles for a few minutes but said I should be thankful as that would cost less than replacing the accumulators. I went to pick up my truck and in person the service rep was even more confused when I asked if they had pulled codes on the AHC system...he replied Your check engine light isn't on. It is actually I reminded him, for an O2 sensor. All along the way I doubt the rep even more than I did to begin with...he simply didn't understand what he was talking about

I asked to speak to the mechanic who looked at my truck. He came out. When I asked how he concluded the shocks were blown and needed to be replaced. He said, Well they are almost 19 years old, and that is one of the cheapest parts to replace. More questioning about codes, and accumulators and it appeared fairly obvious neither the rep or the guy from the back had a clue what he was talking about. The Rep said he couldn't give me a parts quote because the Lexus dealer is closed on Saturday. I asked if the shocks are the same used on the Toyota LC with the AHC system...he replied...Oh yeah, but we have to get Lexus parts. This sounded dubious to me but I honestly don't know if that is true or not.

Long story short. The Dealer was ZERO help. Their diagnostic skills amounted to, Well we can tell that is an original part, it's cheaper, so replace the shocks first. I shared that I wasn't interested in replacing parts until something worked, and reminded them that is why I came to the dealer for their expertise. The rep no charged my diagnostic visit, I am sure so I wouldn't receive a customer satisfaction survey. Serious question. Isn't the whole point of taking your vehicle to the dealer that they supposedly have the best equipment, training, and insight into repairing your particular brand of vehicle ? Incredibly frustrating. A shade tree mechanic can replace parts until something works...that takes no expertise.

I am almost at the end of my rope....I trust the local Lexus dealer even less than the Toyota dealer so unless they have access to some proprietary equipment Toyota does not, I think that will be a waste of time/money too.

Short of replacing both rear accumulator spheres to see if that works does someone here with some experience diagnosing AHC problems have suggestions ? Anyone have decent experience with a dealer or independent shop in North Alabama ? I am willing to drive and pay to find competent help. If I can't find any qualified help, I may have no option but to replace with an active suspension system. (Not what I want but it may be my only hope.). Thanks in advance for taking time to read and share thoughts.

 

[l3n0x]

One thing for sure: If the "shocks" (which are hydraulic rams instead) don't leak or aren't badly rusted, then they are good.

You could do the graduation test on the reservoir & see if the L->N pressures are within specs as an easy diagnostic. Then go from there.

There is a good and detailed thread about troubleshooting and possible issues here. It's a long read, but very worth the time:

Definitive list of AHC maintenance items

My nagging "issue" with AHC is wondering if the suspension doesn't feel quite right. I feel bumps pretty well and I subjectively recall an older 100 series land cruiser standard suspension feeling like being on a cloud vs the small cracks in the road. The question is driving me insane when I'm...

forum.ih8mud.com

 

[uHu]

Heights and pressures at N, and graduations (Lo to Hi), are important inputs to the diagnosis.
But probably, based on age and symptoms, the verdict will be rear spheres (accumulators).
PS
There are many reports of similar experiences with dealers when it comes to ahc diagnosis. The mechs with ahc knowledge are far between.

 

[l3n0x]

Could be the spheres, could be the valves, could be the actuators as well, but agree that most likely it's the spheres.

 

[lawdlc]

Appreciate the input...I suppose the next step is to check levels as described... I love my LX470 but there have been a handful of really PITA problems I (we) have dealt with...the Heater T (mine weeped without detection/unexplained coolant loss for a very long time until I read the threads here and replaced..could have been catastrophic) , the ignition switch lock & replacement, the ignition pot metal piece break and now the AHC suspension issues....all familiar to most owners no doubt... not what one hopes for from Lexus... I hate to say this, but I had fewer problems with a 1995 K2500 LT 6.5 td Chevrolet Suburban I owned for many years (through about 200k miles) and the problems I did have, were much cheaper/simpler to repair...doesn't help my wife drives a Prius...fuel/oil changes/air & cabin filter changes and drive now at about 90,000 miles + one set of Michelins after the factory tires

 

[BEG]

Sorry you're having such a rough go of things. It's a shame, but your experience at the dealer is par for the course when it comes to AHC. All it would take is for them to crack open the FSM, but most are unwilling.

I would recommend to anyone that they save whatever it costs to have the dealer diagnose the AHC and just buy themselves a code reader, whether it be Techstream, OBDLink or, my preference, the iCarsoft TYT II.

As has been mentioned previously, a few simple tests and the diagnostic tool will pinpoint the issue 90% of the time. In your case, the graduation test and the 16 step test will most likely point to flat globes. As the globes age, the membrane that separates the AHC fluid and the nitrogen gas charge starts to deteriorate, either slowly, allowing gas to pass through, or by way of a rupture. When this happens, the spring rate goes way up because there is no longer sufficient gas to compress, and you get a harsh, bouncy ride.

The diagnostic tool will let you know if you are within the pressure range specified by Toyota. If the system is outside of that range by a considerable amount, it will no longer provide proper damping. This can usually be mitigated enough to move on to the other tests by adjusting the torsion bars to increase preload until the system is back within spec, or close to it.

By performing the graduation test, you'll find out if the globes are filled with fluid, since this will yield a lower fluid height delta from L to H than normal.

If you fail the graduation test, you can move on to the 16-step test, where you manually cycle through all 16 damping settings and bounce each corner of the car. Each corner should get progressively harder to bounce as the damping rate is increased. The corner(s) that doesn't respond is the culprit.

None of these are particularly difficult to perform and, aside from a code reader, don't require any specific tools (the graduation test doesn't require any tools and the 16-step requires a paperclip). Just a little bit of specialized knowledge on AHC diagnosis and maintenance, of which there is plenty on this forum.

Take a crack at the tests and post up your results.

 

[baggar11]

Do you have any records on if the rear springs have ever been replaced? That's my bet. It's pretty common that aging rear springs will push more of the load onto the AHC system and cause the bounciness. Try getting some AHC numbers from Techstream and you'll know for sure.