Another AHC Question

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T

tomsawyer

10 Year
Joined
Nov 7, 2015
Threads
17
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49
Location
North Jersey
Hey Everyone - I did a search but didn't see this particular issue but I'm sure for the more experienced people this might be an easy one but not for a newbie. I have an 03 w/ 94k.

I have the AHC set to N and I believe everything is operating/set to where its supposed to be. To the naked eye, the truck looks like a normal height, not sagging anywhere, etc. When I switch the AHC to Low, the truck goes down like I believe it's supposed to and sits low - the light is solid green.

However, if the truck is set to N and I set the switch to High, the truck starts to move up. The H light is solid green. Then, at a certain point, it seems like the system is "struggling" to make it to the highest point and the system gives up, drops and goes back to N - and then the OFF light starts blinking. If I shut the truck off and restart it, the blinking off light goes away. Any idea what's going on?

Thanks to all who answer.
 
What is your fluid level? When is the last time you flushed the fluid? It is easy for the truck to drop down, as it is just releasing hydraulic fluid back into the reservoir, but to go to high it has to build more pressure. The first thing to start with is the condition of your fluid, since if it is contaminated, your system is working very hard to try to build that pressure.
 
If you read a few posts on the ahc, you'll find your problem covered.
The weight of the truck is carried by both the steel springs (rear coils, front torsion bars) and the ahc gas spheres. If the springs are old and weak (>5 yrs), or the height of the truck is adjusted up, there will be too much lifting to do for the ahc system. You need to check your heights and to measure the ahc neutral pressure in order to find the condition of the springs.
 
I hope this isn't a stupid question, but I'm just using the truck as a daily commuter - no off-roading or anything like that. I don't have any precise measurements or the capability to measure what's going on but in normal mode, I believe the truck to be riding nicely and adjusting slightly up and down (I'm not talking H - N- L) but rather slight height adjustments based on various conditions, such as parked, highway. If everything is working ok in N mode, do I need to worry about H if I'm not using it?

Thanks
 
That's not a stupid question, quite reasonable actually. Here's my take on it. Firstly, you should bear in mind that not only is it an active height control system it is also an adaptive variable suspension system and the two are intrinsically linked. Now if, as @uHu stated above, your neutral pressures are high - and it is 99.9% guaranteed they are if the system hasn't been regularly maintained and adjusted - due to your mechanical springs aging and taking a set or being too high then the consequences are: reduced load carrying capacity; inability to lift itself to H; accelerated external leakage in the shock actuators; accelerated wear on other components like the height accumulator and damper accumulators and degraded, harsh damping. It's the harsh, degraded damping that is usually the first thing people observe and identify as an issue. So do you need to worry about not raising to H if you're not using it? Well yes, it should be addressed just for the sake of improving your damping and not unduly stressing the system.
 
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I would not necessarily overthink this. Suspensions can be complicated, especially if were talking torsion bars, IFS, and AHC. Sounds like in general you AHC is in working order. I think the simplest place to start is to just to PM on the AHC and flush the fluid. I did this with a buddy in the last couple months and I would estimate it took 30 minutes, most of the time spent removing the old fluid from the reservoir. There are great write-ups on here and it really was straight forward. We each used 1.5 bottles of fluid, so keep that in mind.

Following that as uhu stated, your stock mechanical system (the torsion bars and rear springs) have probably relaxed over time and are relying more heavily on the hydraulic system to pick up the slack. This will cause early failure of your system, even in neutral height. Adjusting the torsion bars is a pretty easy task, but you really should have techstream to tell you the fluid pressures when you turn or "pre-load" the torsion bar to get the pressure back to the correct range. Keep in mind, these pressures are massive, like ~700 psi, so this is not something you ill measure like a vehicle tire, and why you need the techstream.

I am not sure if you can find someone locally with the techstream, or just buy the module and download the software. My understanding is you can pick up this equipment for very cheap considering. Since you are from New Jersey, just make sure you soak your bolts, nuts, and anything that you plan to turn with PB Blaster at least the day before you adjust things. Currently, you know your system is "kind of" not working, its way easier and less expensive to treat it now before it "really" is not working.
 
PADDO said:
That's not a stupid question, quite reasonable actually. Here's my take on it. Firstly, you should bear in mind that not only is it an active height control system it is also an adaptive variable suspension system and the two are intrinsically linked. Now if, as @uHu stated above, your neutral pressures are high - and it is 99.9% guaranteed they are if the system hasn't been regularly maintained and adjusted - due to your mechanical springs aging and taking a set or being too high then the consequences are: reduced load carrying capacity; inability to lift itself to H; accelerated external leakage in the shock actuators; accelerated wear on other components like the height accumulator and damper accumulators and degraded, harsh damping. It's the harsh, degraded damping that is usually the first thing people observe and identify as an issue. So do you need to worry about not raising to H if you're not using it? Well yes, it should be addressed just for the sake of improving your damping and not unduly stressing the system.
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Guys, I appreciate all the info. Unfortunately, I am not very mechanically inclined nor do I have the tools to do certain things. As such, if I wanted the AHC/suspension system diagnosed/tested, is that something I would need to take to the dealer to do? I'm in northern NJ and I don't know of any Lexus/Toyota indy's around here (unless I'm not looking in the wrong places?). So, if you do recommend the dealer, I know they charge by the hour but how much would you think a diagnosis/suspension adjustment with fluid flush cost? Thanks
 
I feel you, but fluid flush is really really easy. I just did it myself based on a write up here. You literally need one tool. Paddo is the guru of AHC, and you need to address this in the medium to long run. But a fluid change is cheap, easy, and gives some insight into your system.
 
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