Help Diagnosing AHC issue (1 Viewer)

[aphil]

Hey! So I just picked up my (new to me) '99 LX470 with 167,000 miles a few days ago. When I did the test drive everything on the AHC seemed to work fine, but i'm starting to notice some irregularities with it and after much reading I'm thinking it has to do with the pump but not totally sure. It seems to be inconsistent when raising and lowering when stopped.

Turn car off: drops to low sometimes, but other times just stays in N
Turn Car on: Stays in current height and moves to N when driving
Pressing UP or Down or N when stopped: Sometimes will move into position, other times it just blinks. Sometimes it moves to the correct position but just continues blinking. Sometimes it doesn't move but keeps blinking.
Pressing up when stopped: sometimes it moves only the rear up. Sometimes it moves front and rear up. Sometimes nothing happens and the light just blinks
Driving: It seems to automatically move to the correct positions when driving. Moves to N from L when over 5mph and moves from H to N when over 20mph

Comfort/sport mode: Works as expected
AHC Fluid Level: 6 notches between Low and High

So, overall it always automatically moves to the N position when driving, the ride is fantastic and the comfort and sport setting seems to work well (although I don't have a point of comparison). It can move to the low and high positions manually but this behavior is inconsistent - sometimes working, other times not or sometimes taking a very very long time to finally move.

Anyone with experience with this AHC system able to shed any light on this? Thanks!

 

[aphil]

Anyone have a guess on this?

 

[RoaringFork]

I would recommend getting under the truck and giving the AHC system and good inspection. Check the level sensors for damage, check the globes, accumulator, pump for leaks...

Then i would start by flushing the fluid, cheap and easy. You mentioned the level was ok, how is the condition? Degraded/contaminated fluid can cause problems as you describe. After a fluid flush the next step would be acquire techstream(diagnostic software that will talk to the AHC computer), then check for faults, and check the operating pressures.

Replacing anything other than fluid without techstream would just be guessing.

I’ll try and find the threads regarding flushing and techstream.

 

[RoaringFork]

Props to PADDO's AHC fluid replacement method!

I just had my AHC fluid replaced. My local indy shop quoted me over 3 hours labor. After reading many posts here that people were getting it done in an hour or less, I reached out to PADDO for advice. He provided me a step by step process that I gave to the local shop. They ended up following...

forum.ih8mud.com

Post #4 describes the “ @PADDO ” method of the flush. I can attest it works as I have done it this way to my family hauler...

 

[RoaringFork]

...and techstream info

How-To: TechStream In 5 Minutes

Getting Techstream up and running can be a bit of a pain. Hopefully this helps someone get started quickly. Step 1: Purchase an OBD-II / Mini-VCI interface. - I have sold out of my cables and supply chains are back in order, so no reason to purchase more. Anything like this will work: Mini-VCI...

forum.ih8mud.com

 

[RoaringFork]

Good luck, keep us updated on what you find!

 

[aphil]

Thanks for the pointers. I didn’t realize the fluid could cause the irregularity in function like this. Anyone know the best place to purchase the AHC fluid?

 

[RoaringFork]

Thanks for the pointers. I didn’t realize the fluid could cause the irregularity in function like this. Anyone know the best place to purchase the AHC fluid?

Your local Toyota dealer... it’s cheap. My dealer didn’t stock the “cans” so I had to buy 1qt containers. You will have half of one left over...

When I flushed my 06, I purchased 5 1qt containers and flushed it twice(using the @PADDO method), just for peace of mind. I had no issues with the AHC, the fluid level was a little low, but dirty. Without having records of a flush being done, I figured it was best for maintenance...

 

[RoaringFork]

...or Lexus dealer

 

[uHu]

A lot of what you are asking is already covered in several threads in here. You need to become more familiar with the AHC system (read mud and FSM for a day or two) and with TechStream (or similar). Without TechStream and the FSM it's like a blind man building a house.
I suppose you know that AHC will not move if a door is open, or if the height difference between two wheels is to big.

From your symptoms it sounds like you either have a bad sensor, sensor link, cabling/plug; or that your pressure is too high; or both.

 

[aphil]

So, I've checked all the components visually. Don't see any leaks, but the AHC fluid in the reservoir is dark green/black. I'm going to start with the fluid flush and see how that effects things. The other strange thing I'm noticing is that many times just getting out of the truck and getting back in will get it to move into the correct position. Could there be a door closed sensor that's off?

I'm also wondering if the system needed some time to get used to running again. The previous owner had it for 4 years and said he never touched the AHC buttons on the console. They also hadn't driven the truck for a few months and it had just been sitting. I'm only wondering this because it seems to be working more consistently now after lots of up and down adjustments the past few days

I've read nearly every thread on the AHC on mud over the past 3 days and have not found someone having this intermittent working/not working issue or maybe the search function isn't pulling up the correct threads.

 

[uHu]

You are noticing how the ahc works. It's Automatic Height Control, meaning that it controls the set height automatically, not primarily a height adjusting feature. That means that it will automatically adjust the height, without your input, whenever it feels that one axle is out of spec height. The ahc will always work, even when you don't touch the buttons for years. It will adjust the height when you go uphill, when you go downhill, when you stop, when you speed, when you add or remove weight; but only in certain conditions. It will always wait a bit and check height over time (a few secs), and might well adjust when you start up again. All this is in the introduction to the ahc in the FSM and in a few forum posts here. I've posted your search terms under here, gives you a few threads to start with.
And here is one of the important ones - maybe a place to start: forum.ih8mud.com/threads/definitive-list-of-ahc-maintenance-items.604577/

 

[aphil]

UPDATE

flushed the system using @PADDO ’s method. Drained the reservoir (fluid was nearly black). Added 2.5 liters new fluid in. Bled 1 liter from the bottom the DS accumulator and PS globes combined. Started car and moved to N. Then turned off and bled a bit more from DS globes. Then restarted and cycled through the L N H. It seems to be working perfectly now. It moves quickly and consistently into each level within a few seconds. I may have overfilled the reservoir bc in NORMAL I had an inch over the max full line so I sucked an extra half inch out to get closer to that max fill line. Now I have about 8 or 9 lines between the HIGH and LOW position in the reservoir whereas I previously only had 6 with the old fluid. Hopefully the fluid flush was all that was needed thanks for the help!!