LX470 Suspension Goes Into Full-Hard Mode By Itself

Tinkerer · 10-04-09, 11:50 AM

Anyone experienced the following with their LX?

After about 40 minutes of highway driving, the suspension becomes stiff, like the "Sport" or full-hard mode. When that happens, it stays in this stiff mode, regardless of user setting.

Shutting off engine and restarting will reset the system to user-set mode, e.g., "Normal" or "Comfort" or whatever user sets.

Happens repeatedly now, with my 99 LX.

Any info appreciated.

TIA - T.

STEVEN XU · 10-08-09, 03:25 PM

The fault of any one of the 3 height sensors might result in this kind of AHC problem. It may not bring up any warning light on the dashboard, but can be detected by checking DTC. Faulted height sensor fools ECU, ECU interprets that suspension is sagged, then pump is activated to compress the absorbers, making the suspension stiff.

Tinkerer · 10-09-09, 06:36 AM

Quote:

Originally Posted by STEVEN XU

The fault of any one of the 3 height sensors might result in this kind of AHC problem. It may not bring up any warning light on the dashboard, but can be detected by checking DTC. Faulted height sensor fools ECU, ECU interprets that suspension is sagged, then pump is activated to compress the absorbers, making the suspension stiff.

But if ECU interprets that suspension is low and activates pump, wouldn't that raise suspension height?

The problem exhibited by my 99 LX is that the suspension damping becomes stiff, like "Sport" mode, by itself (without any user input), regardless of mode setting at the mode setting dial. It does not raise or lower the height when this happens.

When this happens, suspension may be restored to normal operation by shutting off and restarting the engine.

It only happens after about 40 minutes of highway driving.

SWUtah · 10-09-09, 12:53 PM

Quote:

Originally Posted by Tinkerer

But if ECU interprets that suspension is low and activates pump, wouldn't that raise suspension height?

The problem exhibited by my 99 LX is that the suspension damping becomes stiff, like "Sport" mode, by itself (without any user input), regardless of mode setting at the mode setting dial. It does not raise or lower the height when this happens.

When this happens, suspension may be restored to normal operation by shutting off and restarting the engine.

It only happens after about 40 minutes of highway driving.

If you haven't changed your fluid that might be the problem.

LXPearl · 10-21-09, 06:47 PM

It sounds like a problem in the AVS system. It could be old fluid, but also could be a shock gone bad. I had a bad front shock replaced under warranty (both) and the ride was significantly improved. So smooth.

uHu · 10-22-09, 03:57 PM

Could it be that someone forgot to remove the diagnosis jumper in the DCL or Diagnose plug?
When that short-plug is in place, the damping is adjusted one step up (to 16) for each time you step on the brakes.
Long shot

Tinkerer · 10-23-09, 04:47 AM

Problem was first observed while the vehicle was under warrenty in c. 1999-2000, although at that time it would not manifest except rarely. Dealer could not duplicate it, said they did not know what might have caused it. (They probably thought I was imagining it.)

It has gotten gradually more apparent (during highway trips) over the years. Last 200 mile interstate trip, it happened about every 40 minutes, or several times, during the trip.

The fluid was thoroughly changed at about 90k+, using Toyota replacement fluid. Now at 127k+.

Everything else about the AHC system appears to work properly. (I have had the vehicle since new, I would notice unusual operation of the system.)

Any other suggestions/comments appreciated.

uHu · 10-23-09, 10:49 AM

But really, have you checked for the presence of a short-jumper in the DLC3 connector under the dash and in the diagnosis plug in the engine compartment?

tom. · 10-27-09, 01:14 PM

Where is the diagnosis plug in the engine compartment?

Texasoil · 11-07-09, 10:29 AM

on-top of front passenger side fender well.

Never heard of this particular problem Is it TIME related or DISTANCE related? An electronic circuit failing would be temperature sensitive--fails when it finally gets hot enough. If the symptom is not regular, it MAY be caused by a poor connection on the cable plug to the AHC computer. This type of problem is almost ALWAYS caused by a poor connection someplace. Hard parts (the 4 suspension stiffness valves by the accumulators) simply do not behave this way.

It could be caused by a bad ground in the AHC wiring harness somewhere. This is what it 'sounds like' to me. Find all the electrical ground points and tighten/clean them up.

I use a product called 'Stabilant 22' for ALL electrical connections. The stuff was developed in Canada by for good chemists, for a long time was a military secrete and not available commercially. Your good autoparts store can order it for you (about $70 for 10ml liquid kit)--a lifetime supply. It is in the tool box of every IBM and XEROX service tech, exclusively used in all military and aircraft electronic/electrical installations and servicing. It even significantly improves connection quality of clean gold to clean gold!!