AHC "Off" light flashes occasionally

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ThirdShore

ThirdShore

10 Year 15 Year
Joined
May 31, 2009
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10
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96
Location
South Carolina
AHC "Off" light flashes occasionally and AHC won't function properly. 2006 LC with 75k miles, and to my knowledge the fluid hasn't been changed. I inquired about changing the fluid it at the 60k maintenance, but the dealership said it wasn't recommended per there recommended maintenance, even though my printed maintenance guide says to change the fluid at that point.

Any ideas on the most likely cause of this occasional failure? I don't know if it's all in my head, but the ride seems bumpier than it did when I purchased with 55k miles.
 
Check your AHC fluid levels. I had the same issue when going into HI. Fluid wasn't available and the pump was just pumping air. The car would drop back to normal height and ride level control didn't work. You may be having the same issue, but with even less fluid than me :hhmm:
 
Joebu33 said:
That seems likely. The level is low. Hopefully flushing the system will get me back to a smoother ride as well.
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Let us know the outcome.
 
Is it also possible that the accumulators need to be replaced? I'm no expert on this kind of stuff...just trying to learn.
 
Don't think the accumulators would make the light flash.
 
If the accumulators go flat, there is more room in them for fluid, thus lowering your fluid level in the reservoir and possibly causing the symptoms OP described.
 
Ahh, I stand corrected.
 
hkeller said:
If the accumulators go flat, there is more room in them for fluid, thus lowering your fluid level in the reservoir and possibly causing the symptoms OP described.
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I was wondering about that. I figured the level wouldn't drop so much unless there was a leak???
 
So the dealer just added fluid to the reservoir. They didn't flush the system, and they didn't test the accumulators. I could have done that. I feel like this will address the AHC "Off" light flashing issue, but I don't feel like this will take care of the root of the problem. By the way, it took them from 7am to 5pm to do this.

The ride doesn't seem to have improved with the additional fluid, and I'm not sure if it's all in my head, but it just seems rougher than I remember from my first day in the car (as I recall it used to feel like it was gliding on the road). I know it's a truck, but I just want it performing to up to its capabilities.

I'm wondering if the initial reason the fluid was low is that the accumulators are going bad, as hkeller stated above, and are possibly in need of replacement. I've never taken a wrench to a car, but am wondering if it's time. Is testing and possibly replacing the accumulators something that a rookie with determination can do easily/safely enough?
 
If I were you I would either have them flush the fluid or try doing it yourself (there are numerous posts with good instructions). It is recommended at 60k for a reason and I am surprised that the dealership said you don't need to follow the recommended maintenance.

You can 'test' the accumulators yourself using 2 methods (see site.activesuspensionsystems.com Blog / FAQ: Lexus LX470 and Toyota Landcruiser 100 accumulators. for details). Method 1 is checking the # of gradations from L to H, method 2 is the 'curb test'.

Even if you 'fail' the curb test, I would flush the fluid to see if it improves the ride. If you fail the 7 gradations test there may not be any point in flushing the fluid 'cause something else might be wrong (either pump or accumulator bad etc).

Let us know how it turns out. Personally I flushed the fluid at ~75k and believe I noticed a significant difference.
 
agaisin said:
If I were you I would either have them flush the fluid or try doing it yourself (there are numerous posts with good instructions). It is recommended at 60k for a reason and I am surprised that the dealership said you don't need to follow the recommended maintenance.

You can 'test' the accumulators yourself using 2 methods (see site.activesuspensionsystems.com Blog / FAQ: Lexus LX470 and Toyota Landcruiser 100 accumulators. for details). Method 1 is checking the # of gradations from L to H, method 2 is the 'curb test'.

Even if you 'fail' the curb test, I would flush the fluid to see if it improves the ride. If you fail the 7 gradations test there may not be any point in flushing the fluid 'cause something else might be wrong (either pump or accumulator bad etc).

Let us know how it turns out. Personally I flushed the fluid at ~75k and believe I noticed a significant difference.
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Do you have a thread anywhere out there on the fluid flush? Would love a step by step.

I have AHC on my 06, and have noticed over the past 18 months the ride is not nearly as smooth as it used to be....80k miles.
 
Can someone explain to me why changing the fluid in a hydraulic (sp?) system improves the ride? I can understand the need to change it as it can get contaminated through movement of "shocks"; Contaminates could then interfer with sensors, valve gates, etc. However, I just don't get how a fluid change should impact the ride quaility whatsoever.
 
hkeller said:
Can someone explain to me why changing the fluid in a hydraulic (sp?) system improves the ride? I can understand the need to change it as it can get contaminated through movement of "shocks"; Contaminates could then interfer with sensors, valve gates, etc. However, I just don't get how a fluid change should impact the ride quaility whatsoever.
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My understanding is that moisture and other contaminants get into the fluid over time. Hydraulic fluid doesn't have the same properties once it gets contaminated with water etc. Therefore the ride quality would be impacted.

Interesting that other auto manufacturers with hydraulic suspension apparently have shifted to LHM (Hydropneumatic suspension - Wikipedia, the free encyclopedia@@AMEPARAM@@/wiki/File:Merge-arrows.svg" class="image"><img alt="Merge-arrows.svg" src="http://upload.wikimedia.org/wikipedia/commons/thumb/5/52/Merge-arrows.svg/50px-Merge-arrows.svg.png"@@AMEPARAM@@commons/thumb/5/52/Merge-arrows.svg/50px-Merge-arrows.svg.png) that does not absorb water (i.e. hygroscopic). I don't know what kind of fluid Lexus/Toyota uses, whether the water absorbption is a myth or if it's b/c Lex/Toy haven't switch to this other kind of fluid? Can anyone else out there shed any light on the topic?
 
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AHC fluid why change?

'LHM' is the trademarked abbreviation CITROEN uses for their mineral oil (petroleum) they switched to around 1970 (from brake fluid) Brake fluid just loves to soak up water and then start deteriorating into corrosive acids and junk. LHM does not absorb water , Brake fluids are DESIGNED to dissolve water to ensure there are no droplets around to freeze or boil.

LHM is, in my opinion, a very good substitute for Toyota AHC fluid in a pinch. It will not harm anything. Likewise, the BMW and MBZ hydraulic suspension fluids are excellent substitutes.

NEVER use brake fluid. Even small amounts (AN OUNCE) will cause quick failure of the accumulator diaphragms and work on all the other 'rubber' containing parts in the AHC system (about $14,000 worth to buy and R&R at a Dealer book rate)

The AHC oil should be changed at least every 30K miles, or any time the oil in the reservoir does not look new. Oil is cheap compared to the damage old oil will allow. The itty bitty tennie weenie hydraulic pump quickly wears out if the oil is old, the weather is hot, the oil is hot, and the vehicle is loaded. Dealers are happy to sell and install the entire reservoir, housing, sensor assembly ($2100 part + 5 hours) when the pump subassembly (for about $285) and an hours is what is needed.

If the oil has deteriorated to the point it looks dark, black, milky--flush the system thoroughly, drive a week and repeat until it stays as new. There is no filter in the system, and dark oil is one marker of serious contamination. The reservoir oil should look as new--always.
 
Sorry to bump an old thread like this but does anyone else have experience with using LHM over Toyota AHC fluid? Main reason is that LHM is easy to get here but Toyota's fluid has to be ordered from abroad.
 
To add some context I also have an occasionally flashing AHC light and getting error code C1776 (RF sensor) which is most likely corroded at 127K miles in Sweden (harsh winters + salt). I will remove it and see if i can clean it. It looks like the AHC fluid never has been changed and the globes are probably not in top condition (got 7 marks between high and low last time i checked).

Bottom line is I don't want to throw too much money on the AHC system at this mileage and will settle for cleaning up the sensor or changing it and flushing the AHC fluid. I would like to keep it somewhat working for a few more miles though.

The fluid seems pretty much unattainable except through Toyota dealship while LHM/LHM+ is very available. Probably becausae Citroëns are common here.
 
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