Rear end up in the air (AHC)

[2001LC]

I've no experience with AHC. My 01 LX (new to me) is on the same jack stands I've use for the LC. But front tires are on ground and rear is high in the air. What going on???

What little I do know about this rigs is that in Nov 2014 a shop report stated: "rear shock leaking, recommend replace all due to age". No record or sign of any every being replaced. The AHC fluid is below low level.

Reservoir pic's is with rig on stands. Front jack stands are under frame with rears supporting axle/differential (rear tire off ground).

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[PADDO]

The fluid level is ultra low because the shock actuators are at full extension. Conversely, with the wheels on the ground and when you go to LOW the fluid level in the reservoir rises above its N level. Correct way to check fluid level is when you're on the ground, drop to L, raise to N and wait 30 seconds (leave engine running) to observe the fluid between max and min.
High neutral pressures cause shocks to leak, recommending they be changed due to age (in the absence of an actual failed seal or damage) is BS.
Not following your concern about front tires on ground but rears aren't, compared to your LC there must be different suspension articulation?

 

[2001LC]

It failed to go in low or high (light just blinked) while on the level ground, and fluid level was also as low.

Pic of on sloping ground, front up hill in driveway.

 

[2001LC]

High neutral pressures cause shocks to leak**
Not following your concern about front tires on ground but rears aren't, compared to your LC there must be different suspension articulation

Can you explain what you mean "High neutral pressures". This stuff is new to me, never dealing with AHC before.

I put jack stand under rear axle, too put rear propeller shafts (AKA rear driveshaft) in neutral stance. Propeller shaft slip yoke is extended, as if rear end dangling like when on a lift. Also top of tire to fender distance, indicates rear shock are extended. This has rig tipped forward stands, so that fronts are on ground. Why would rear shock be so extended?

 

[Julian Stead]

Make sure all doors are closed when changing height, this caught me out the first time.

 

[2001LC]

Make sure all doors are closed when changing height, this caught me out the first time.

Does driving also keep from going in low?

 

[Julian Stead]

No, as long as you are below a certain speed then it should work. If you read through PADDO's posts, he explains how the AHC system works and how to maintain it. I serviced my system using the info he provided from previous posts, it was easy to follow and understand. You might have a sensor issue, but if PADDO replies I think he will give you better info than I could on this.

Im a big fan of AHC so it's worth repairing and keeping in my opinion.

 

[PADDO]

Can you explain what you mean "High neutral pressures". This stuff is new to me, never dealing with AHC before.

I put jack stand under rear axle, too put rear propeller shafts (AKA rear driveshaft) in neutral stance. Propeller shaft slip yoke is extended, as if rear end dangling like when on a lift. Also top of tire to fender distance, indicates rear shock are extended. This has rig tipped forward stands, so that fronts are on ground. Why would rear shock be so extended?

"Neutral pressure" are the hydraulic pressures necessary to lift the vehicle to its predefined Normal height as determined by the height sensors. The front and rear are two independent systems (but sometimes they are connected together) and it's the combination of spring and torsion bar forces and hydraulic forces that holds the vehicle up. If the springs/tbs are old and set then the hydraulics has to make up the difference to maintain its normal height, this difference is seen as higher pressures. Same deal if you add weight, the hydraulics has to provide more lift force, again higher system pressures. Now system pressures matter because they oppose the nitrogen precharges in the 4 x damper globes which are remote gas shock reservoirs that absorb fluid pulses (shock compression) and expel fluid (shock rebound) through the electronically variable damper valves. There is an optimal design balance between system pressure (6.9MPa front and 5.6-6.7MPa rear) and globe precharge that provides the best damping responses. If the system pressure is too high then damping is harsh, too low and it is over sprung. Having neutral pressures optimized for your vehicle is crucial for the adaptive variable suspension to work as designed.

Regarding your shock extensions: front shocks have 5 3/4 in stroke and the rears have 8 3/4 in.

 

[PADDO]

Does driving also keep from going in low?

Low mode is restricted to a couple of mph, it's really for hooking up a trailer, helping granny or old dogs get in/out, low garages etc. Its not a normal driving road mode, neither is High for that matter as it's also speed dependent (unless bypassed). A normally operating system will always return to Normal height regardless if you turn it off, put it in Low or High as a function of speed.
Things that inhibit the ability to go up/down are not turned OFF, doors or back hatch open and foot on brake more than 5 seconds. Whilst stationary with doors shut, engine running and foot not on brake it should raise/lower and OFF should not be flashing.

 

[2001LC]

"Neutral pressure" are the hydraulic pressures necessary to lift the vehicle to its predefined Normal height as determined by the height sensors. The front and rear are two independent systems (but sometimes they are connected together) and it's the combination of spring and torsion bar forces and hydraulic forces that holds the vehicle up. If the springs/tbs are old and set then the hydraulics has to make up the difference to maintain its normal height, this difference is seen as higher pressures. Same deal if you add weight, the hydraulics has to provide more lift force, again higher system pressures. Now system pressures matter because they oppose the nitrogen precharges in the 4 x damper globes which are remote gas shock reservoirs that absorb fluid pulses (shock compression) and expel fluid (shock rebound) through the electronically variable damper valves. There is an optimal design balance between system pressure (6.9MPa front and 5.6-6.7MPa rear) and globe precharge that provides the best damping responses. If the system pressure is too high then damping is harsh, too low and it is over sprung. Having neutral pressures optimized for your vehicle is crucial for the adaptive variable suspension to work as designed.

Regarding your shock extensions: front shocks have 5 3/4 in stroke and the rears have 8 3/4 in.

Great explanation, thank you.

I pick-up a can of AHC from Toyota Dealer, to bleed system. If I can't get out of N on level ground with doors closed, should I still flush? Any thread you can to recommend for testing, bleeding and adjusting complete system?

My 01 LC FSM won't be of any use with AHC. I need to find the FSM for 01LX, or at least the AHC portions.

 

[PADDO]

The "definitive list of AHC maintenance items" thread has some good stuff in it.
To clarify: engine running, doors shut etc and it is staying at N? is off flashing or solid lite?
This is where I'd say use Techstream to check/clear any AHC trouble codes. This can be done manually too but it's hard to catch the flashing light sequences. I'd focus on getting it to respond to the up/down switch before bleeding otherwise you may be stuck on the bumps if you cant get the pump to run. Top up the fluid to above min and keep the remaining fluid for later and we will go from there. I'll find and attach a general procedure for system check out and manual dtc reading.

 

[2001LC]

Ok, I'll top above minimum and see what I get.

First, I'm doing a big cleaning of engine/transmission/suspension this weekend to help find issues & leaks of any fluid (oil, brake, ATF, etc.) along with improving working environment. So any fluid I then get will be fresh leaks, making pin-pointing easier.

Note: I could not find any records of AHC ever being flushed, during my DD inspection. PO said that the system was working because: "See he/we felt height change" when coming to stop at each stop light. My guess was this was from fluid movement in reservoir, then getting to pump inlet, but just an uninformed guess.

 

[PADDO]

If it was doing small leveling corrections at stop lights then that's positive, that's normal operation to do little incremental corrections. Bigger leveling corrections too often suggests a system that might be stressed or have issues.
Just crystal balling but I'd expect your neutral pressures are very high and the fluid may not have been changed. Get your other stuff sorted and we can work on AHC soon

 

[PabloCruise]

Low mode is restricted to a couple of mph, it's really for hooking up a trailer, helping granny or old dogs get in/out, low garages etc. Its not a normal driving road mode, neither is High for that matter as it's also speed dependent (unless bypassed). A normally operating system will always return to Normal height regardless if you turn it off, put it in Low or High as a function of speed.
Things that inhibit the ability to go up/down are not turned OFF, doors or back hatch open and foot on brake more than 5 seconds. Whilst stationary with doors shut, engine running and foot not on brake it should raise/lower and OFF should not be flashing.

It returns t Normal height at speeds in excess of 19 MPH, eh? Does tranny need to be in Park to make changes to AHC height? Or will N work. I know mine will not make height changes with my foot on the brake.

 

[PADDO]

You can raise to H whilst driving, as long as you're under the limit, 19mph? It will drop to L too as long as you're below the lower speed limit.

 

[2001LC]

PADDO, I'd like to clean the reservoir tank internally, before added new fluid.
Is the reservoir easily removed?
If so do you have any tips on how?

Thanks,

 

[PADDO]

Just two bolts holding the reservoir to the pump assembly, front and back of reservoir base. There is a grommet between the reservoir and pump intake that is easily broken if you're not careful. It's listed as a non reusable seal.
If you remove the reservoir you may need to manually drive the pump to get it to prime and make pressure on reassembly and filling.

 

[2001LC]

Great news, you're right system is working. This really makes me feel better about this purchase.

***
High neutral pressures cause shocks to leak, recommending they be changed due to age (in the absence of an actual failed seal or damage) is BS.
**

You're right, PO's shop was full of BS when they said "rears leaking, recommending replace all 4". No leaks see on any shocks in 12 hours in H. However I may have a small leak at rear PS damping globe.
This PS rear looked a little wet, during pre inspection.
What's under that slightly wet cover at tail end of globe? >>>>>>>VVVVVVVV

Just two bolts holding the reservoir to the pump assembly, front and back of reservoir base. There is a grommet between the reservoir and pump intake that is easily broken if you're not careful. It's listed as a non reusable seal.
If you remove the reservoir you may need to manually drive the pump to get it to prime and make pressure on reassembly and filling.

I'll get the grommet from Dealer, and change when I clean tank & flush AHC. Here's a little very dark fluid I pulled, before topping.

I found both lower ball joint boots are torn. Is this common for 100's with AHC?

 

[PADDO]

That cover protects the connector to the damper valve - 5 pin connector that powers the 16 position stepper motor that drives the variable damper.