Calling AHC experts

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Jul 30, 2009
Hello everyone,

Been reading quite a lot on the site. I have had a 1998 LC 100 4.2TD for a year now, car has 115K miles on clock. I had it fully serviced when I bought it but about 3 month ago a fault with AHC developed.
Symptoms are: AHC would blink OFF and light move to L on startup. this would generally happen after the car has stood still for some time. Usually the next day it becomes ok again.

Just been at toyota for annual service. They saw code C1732. They said they tested the pump and sometime 'it did not provide the correct values' (don't ask). They suggested the pump was fine but the problem was the whole control unit. To their credit they said the part was too expensive (got a quote at EUR 1500 for part alone) and I should rather live with it.

So it does not seem to be a sensor or sphere problem but a random issue with the control unit. The car is in south of France and I am struggling to find a decent specialist that could track down the fault and make an effective repair rather than replacing every component of the system. My specialist in the UK has been very helpful but I am not really mechanically gifted and I don't really fancy the round trip to the UK. He offered a used AHC control unit as a swap but I don't want to try without being quite confident this would cure the problem.

I have been reading extensively the various LC forms on the AHC issues but I haven't come across anything similar to my issue.

Anyone can help me in figuring out best course of action?

Many thanks for your help


I would have thought a component or wiring loom fault is more likely than an ECU fault. It will probably be next to impossible to diagnose when it's working and really needs checking over when it has the fault condition. When it fails, if you switch the ignition off and then try again does it stay failed? How often does the fault happen?
Switching off and on does not solve the problem. Typically I have to wait for the next day and then mysteriously things go back to normal. I would simply push the up button right after start and normal operAtion is resumed. One thing my car does is that front lifts first, then back then car levels.
I don't even know where the control is located so I can't inspect connectors. Toyota dealer told me they didvisual inspection and put spray to help lectric contacts on butnothing was obvious.
That is quite annoying !
Have you ever tried disconnecting the batteries for a while when this happens to see if that resets the fault? I think it might be useful to know if the fault condition is momentary but needs time to elapse for the ecu to reset or if it lasts for hours and an ECU reset doesn't help clear it. If it lasts for hours then a good auto electrician armed with the FSM might be able to track down the fault for you. I don't think a visual inspection of wiring / connectors is going to help much with a fault like this.
Ok, I will give it try.
It's very difficult to track down a decent car electrician these days.
I am not an expert BTW, I'm just filling in till a real one comes along :)
First, 1732 is the Front Leveling Solenoid circuit, meaning you could have a loose connection, most likely at the valve body sitting on the inside your left frame rail.

Second, and the first thing to consider is:
This car is 12 years old. The springs (TBs & coils) are worn out. After 12 years of sitting on those steel springs, they will not give the same "lift" as they used to. That means that the AHC system, gas spheres & fluid, has to do more of the weightlifting. If the coils have not been changed, and the TBs not adjusted, the first thing to do is to measure the Neutral Pressure. That will tell you the state of the springs. The AHC is not designed to lift more than a certain part of the weight and will just give up if the steel doesn't do it's part. The AHC Neutral Pressure can be measured by a mechanic with a LSPV gauge kit and the FSM.
My guess is that you will have to change the coil springs in the rear, while you might get away with adjusting the TBs up front.
Now, if the gas spheres have not been changed ever, they will also be quite worn, particularly as the steel springs are getting lazier. So, you have to consider whether to start changing AHC parts, or just give it up and change to conventional suspension.

Now, if you want to keep the AHC, I suggest checking the cable & plugs between the ECU & the valve body, as well as the valve body and the ECU itself. All details in the FSM. Next, and compulsory on an AHC-system more than 5 years old, check the Neutral Pressure. Another thing that can screw up the system without giving reliable trouble codes is faulty height sensors.

Would you have a picture showing where the various items are so I can check for loose connections ? the FSM that I got from the internet does not cover the AHC....

I agree things are getting a bit old in there. the TB bushes were all changed recently but springs are original. AHC got totally flusher a year ago any new correct fluid in. Sensors were checked by toyota apparently and said to be ok.

many thanks for your help
The lads seem to have it covered. I like:
a) Disconnect battery for 20 minutes to reset the ECU without moving the car first when the problem occurs, or doing anything else, and see if the problem goes away. If the problem does go away, it may go away permanently, since the ECU volatile memory has been cleared. I fixed a problem with my steering wheel power tilt motor that way.
b) Check Normal Position pressure. I'm not sure it was Torsion Bar bushes that would have been changed. Probably bushes on other suspension components, since I don't think TBs have bushes. Anyway, if someone did work on the suspension, they may have loosened the TBs and not adjusted them back to original position. The TBs may also have sagged, and need tightening anyway.
c) Inspect and clean Actuator electrical connectors. Mind you, they are somewhat difficult to get at, and difficult to disconnect to inspect. You will find the most likely suspects by looking under the car at the spheres which are connected to the Actuators which have the electrical connections. Also trace back the wiring underneath the car and check connectors you find.
Ok thank you all fr your help. I will try this.

Can anyone point me to where I could download the few relevant pages of the FSM that deal with the AHC ? just to help me locate the various connectors... I am not very gifted with mechanical / electrical stuff.


Search is your friend, as they say:). E.g. this thread could come up: where there is an illus of the actuator where you find the bleed plug for connecting a pressure gauge. The bleed plug is not marked on that pic, but it looks just like any bleeder.

A toyota dealer should be able to provide a manual, at least if you pay them.:popcorn:
Otherwise, I've seen them for sale on Ebay. (I have put it as a condition when buying a new car, that it would come with a full set of manuals)

Here is a "problem symptoms table" to start you off:banana:. I have to add that it doesn't cover all the situations you may experience; and that most dealers / toyo-garages:wrench: do not comprehend how the system works:hmm:. Further I've noticed that the condition of the height sensors are not covered when it comes to symptoms, and, more importantly, the toyota tester can not detect sensor problems as they don't normally give trouble codes even when completely FU.

(My son demanded that I use some smilies (you NEVER use ANY), so I've scattered a few):bounce::clap::cool:


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Many thanks. One last question: where exactly is that valve body connection ?

then I will have to get started:wrench::wrench::wrench:
Just follow the pipes from the actuators. They all end up connected to da valve body, together w the one from the pump, and the accumulator.
AHC parts:


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Looks clearer now.
I will investigate. I guess for the connectors, the best is to unplug, look for loose wires, clean up and apply some connector spray and put things back together.
Many thanks for your help, I will give it a try next weekend.
AHC diagnosis help

Texasoil here an AHC knowledgeable guy in Houston

send me a private email ( and I will email you jpg's of all the repair manual pages showing how YOU can perform all the diagnostics that a qualified Dealer Tech can do--no special anything needed.

If the system, when hot, will raise from L to H in about 30 sec or less, the hydraulic pump is OK.

The post about adjusting the torsion bars are correct. When the shop reinstalled them, they apparently did not properly adjust them, which means the hydraulic system has to increase its pressure to support the vehicle at the selected ride height (L,N,H).
Just tried to clean all connections. Unfortunately no success.
PM sent
Quick update for these interested.
Spent an hour last weekend under the car cleaning and spraying every AHC connector I could get my hands on. No champagne though.

Car is now booked with one of the recommended specialists in the south of france. They sounded very professional over the phone. They take out a lot of AHC for guys that wanna go wheeling in morocco and stuff. They offer a swap of second hand low-ish mileage ECU and spheres at very competitive price.
Car is 115 K miles so I guess the sheres were due for a change anyway.

Thanks a lot for the support, comments and recommendations. Will post when I have the car back....


My view with the AHC is that once it goes bad I'll have it replaced with a conventional suspension. I have yet to use it for the driving I do anyway.
Hello everybody

Just wanted to give you a quick update on the AHC situation.
Once I had checked the easy things, I realised that anything more comprehensive was out of reach of my non-existent mechanical skills and equipement (thanks guys for Help and info though, all stored for future reference).

Found a specialist in south of France. They have a large business of preparing LCs for rallye / desert expedition. They have a number of new-ish AHC spheres and ECU from cars being built up. They did a replacement of all 4 spheres + ECU + new fluid for EUR 1100 (approx USD 1300), which I think is pretty reasonnable. Given the original system failed after 12 years, I guess this has bought me a few years of service at limited cost (fingers crossed).

Best to all and happy motoring


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