AHC stuck in Lo (1 Viewer)

[astrolex]

Hi all,

Apologies if this has been answered elsewhere, I’m on a road trip with wife and three kids so don’t have time to search forums.

The AHC is showing it in Lo setting and it won’t rise into N or High setting. If I press the down button, it does sink into Lo setting. Pressing the up button brings the car up to what looks to be normal height, but the Lo light remains on. We’ve travelled almost 800kms with this issue without any issues so far.

Fluid levels are good. We have 5 people on board plus a full load in the back and on the roof. Suspension was working fine before we loaded the car up and set off.

Should I be concerned?

Thanks

Michael

 

[jLB]

You may want to read this thread for ideas:

AHC stuck in low...emergency help

Hi all! I am brand new here, first post. 2004 Toyota Land Cruiser Turbo Diesel We are in Nicaragua and I found some good information of how to go through the system and debug the issues, but we are currently stuck in the middle of the jungle and the ride height is set to LOW and won't go back...

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[IndroCruise]

Need to be aware of AHC pressures and the effect of vehicle weight causing increased AHC pressures -- meaning weight of everything in or on the vehicle above its 'stock' weight. If the effect of weight raises AHC pressures beyond the system limits, then the system will protect itself (and the vehicle and its occupants) by dropping to LO height to reduce AHC pressures. This is one of the 'fail safe functions' of the system. If this has happened, the vehicle also will refuse to raise from LO to N height because that requires increased AHC pressures and the vehicle certainly will refuse to raise from N to HI height because that requires even higher AHC pressures.

Short of ditching a lot of weight, this will be hard to fix on the run -- unless inclined to stop and make the adjustments necessary for the weight being carried which means --

• adjusting Front torsion bars to carry a greater share of weight and relieve Front AHC pressures (a few minutes work but allow a half-hour), and,
• adding more weight carrying capacity in the Rear to relieve Rear AHC pressures -- by pre-loading Rear springs with spacers, better still, upgrading these springs, or maybe settling for supplementary airbags inside existing Rear springs which can be inflated to meet temporary load requirements (maybe a few hours work if the parts and the wherewithal to do the job are on hand), and,
• having the wherewithal to measure and monitor AHC pressures.

For future trips, suggest read up in IH8MUD on what can be done to carry the weight described -- not hard, not expensive, there are multiple IH8MUD threads with excellent advice on this.

There are many very heavy LC100's and LX470's all around the world, running very successfully and maintaining all the self-levelling and height flexibility benefits of Active Height Control (AHC) in real time, along with the ride comfort and roadholding provided by the Toyota Electronic Modulated Suspension (TEMS) which provides adaptive variable damping in 16 steps, responding to road conditions, speed, braking, acceleration, cornering, etc, also in real time while travelling, with driver options in four 'maps' from "Comfort" through to "Sport".

Long term excessive AHC pressures and lack of routine AHC system maintenance (at the least per Owners Manual) eventually will result in damage to system seals and valves, leaks, repair bills, loss of the excellent ride comfort, responsiveness and flexibility of which these AHC/TEMS-equipped vehicles are capable, reduced vehicle and system longevity, unhappiness -- all easily and inexpensively avoided with due care.

Load guidance extracted from the Factory Service Manual (based on stock vehicle configuration):

 

[astrolex]

Thanks Indrocruise, that’s all great advice. I have read plenty of the AHC threads on here and had intended to adjust the torsion bars before heading off, but simply ran out of time.

Assuming I can’t lose much weight and the vehicle stays in Lo for the remainder of the trip, will any damage be caused to the system? We’re not travelling off road at all so the current level of clearance - somewhere between N and L - will suffice.

Thanks again

 

[GTV]

At a minimum I'd go find a 30mm socket and give the torsion bars a few turns. Or find a shop that can do it. Once you get home read your pressures and correct them.

 

[IndroCruise]

At a minimum I'd go find a 30mm socket and give the torsion bars a few turns. Or find a shop that can do it. Once you get home read your pressures and correct them.

Agree with above suggestion by @GTV

 

[astrolex]

At a minimum I'd go find a 30mm socket and give the torsion bars a few turns. Or find a shop that can do it. Once you get home read your pressures and correct them.

Ok will try. Do I need to have the wheels off the ground to do this? Which height setting should the AHC be in when do it?

Many thanks

 

[GTV]

Ok will try. Do I need to have the wheels off the ground to do this? Which height setting should the AHC be in when do it?

Many thanks

You're stuck in LO... It's not advised to adjust them in LO so I've never tried. Wheels off the ground and lubing the adjuster threads first will make the bolts easiest to turn.

 

[astrolex]

You're stuck in LO... It's not advised to adjust them in LO so I've never tried. Wheels off the ground and lubing the adjuster threads first will make the bolts easiest to turn.

I’ve unloaded everyone and everything and can do get into N and High.

 

[GTV]

I’ve unloaded everyone and everything and can do get into N and High.

Put it in HI, it will be fine.

 

[IndroCruise]

Ok will try. Do I need to have the wheels off the ground to do this? Which height setting should the AHC be in when do it?

Many thanks

As indicated by @GTV while I was writing, it is easier to wind the torsion bar adjusters with the vehicle on the ground in HI height setting on a level surface engine and AHC OFF, or, with wheels off the ground -- because the torsion bars are carrying less load in those conditions -- if you can do either while camped and much of the load and persons are out of the vehicle.

Hit the adjuster threads and mechanism with generous thread penetrating lubricant several times, wind the adjusters clockwise looking up from below, equally on both left and right sides, say four turns because the loaded vehicle as described really is quite heavy. Four turns is nothing more than a wild guess because the current actual AHC pressures and the actual weight of the loaded vehicle are unknown -- but it seems unlikely to need less than this. The only consequence of overdoing it is too much weight carried by the Front torsion bars, then Front AHC pressure becomes too low, then there is less damping capability and the ride becomes a little 'springy' -- but at least more weight is now being carried by the torsion bars.

Back off the torsion bar adjusters if road test suggests this is necessary, or wind more turns on if felt necessary. Without Techstream or other suitable scanner, the only measuring tool is backside-in-seat. After adjustment, drive around the block to see what the change feels like, allow the suspension to settle into the adjusted position and then check Front 'cross level' -- measure with a tape (or a piece of string or marks on a stick) hub-to-fender at Front LHS and Front RHS -- these need to be equal (to load the torsion bars equally) otherwise the ride and steering will feel different on Left turns versus Right turns.

This effort will transfer weight from the Front AHC system, basically from the 'shock absorbers' (which really are weight-bearing hydraulic struts on an AHC-equipped vehicle), to the Front torsion bars. Damping actually is done at the Damping Force Control Actuators to which the 'globes' are attached, not in the mis-named 'shock absorbers' whose primary function is to regulate the height of the vehicle under the control of the Suspension Electronic Control Unit (ECU) and signals from the Height Control Sensors (two at the Front, one in the Rear).

It also is important to have more travel in the Front suspension than is available at LO height setting -- otherwise there is not much distance to the bump stops and the Lower Control Arms will take a beating in rough conditions. Cracked Lower Control Arms are a known issue in Australia. Later, when suspension work is done on the vehicle, suggest include the prescribed reinforcements in this area.

The Front AHC system and the Rear AHC system are not hydraulically connected but changes at the Front will have some effect at the Rear.

The Rear AHC pressures almost certainly will remain excessive, especially when much of the load will be towards the Rear while travelling. Not much can be done about that on the run -- just be conscious of it and go easy on the vehicle, go slow in any rough conditions encountered.

Suggest check that the level of AHC Fluid in the AHC Tank is adequate. If it is necessary to add fluid, use only genuine Toyota/Lexus AHC Fluid Part Number 08886-01805 -- it might be a struggle to find a Dealer open for business in Adelaide before Tuesday to get this stuff over the counter. The need to add AHC Fluid would indicate that the fluid has gone somewhere -- and there are only two places for it to go -- into failing 'globes' (cannot do much about that short of changing out the 'globes'), or, fluid is leaking out of the system -- so check for leaks around the AHC system under the vehicle, especially around the 'shock absorbers'. Damp-looking 'shock absorbers' due to a minor leak can be lived with -- but monitor closely. A major leak which accumulates on the ground is a much more serious matter -- needs to be fixed before roaming to remote places.

For all of that, enjoy the trip!! The Flinders Ranges and Lake Eyre should be spectacular after the recent rains. If you can set up camp and remove much of the load except passengers from the vehicle, you will be able to explore the environs freely in a relaxed frame of mind. There are lots of great trails in these areas -- some of the tracks in the North Flinders around Arkaroola are spectacular.

Whatever else, don't forget to carry plenty of water and make sure that someone else has details your travel plans and whereabouts over time. Mobile phone reception will be non-existent in much of these areas. Suggest consider hiring a satphone for emergencies and breakdowns.

 

[suprarx7nut]

I'd go 10 turns up on each side or until you run out of adjustment. If you're unable to hit N you're way over spec on pressure.

Get the car in H and use a breaker bar with some WD-40, penetrating oil, etc..

Enjoy the trip!

 

[AtinLango]

I'd go 10 turns up on each side or until you run out of adjustment. If you're unable to hit N you're way over spec on pressure.

Get the car in H and use a breaker bar with some WD-40, penetrating oil, etc..

Enjoy the trip!

This is very useful. So if I don't want to jack up the car, I would just raise it to H and be able to turn the torsion. Is this right?

Secondly, using WD-40, where exactly should one spray it?

 

[suprarx7nut]

This is very useful. So if I don't want to jack up the car, I would just raise it to H and be able to turn the torsion. Is this right?

Secondly, using WD-40, where exactly should one spray it?

1. Yes. Adjusting the torsion bar is easier in H. It's still laborious, but easier.
2. On the adjusting bolt threads where the nut is.

 

[AtinLango]

1. Yes. Adjusting the torsion bar is easier in H. It's still laborious, but easier.
2. On the adjusting bolt threads where the nut is.

Appreciated!

 

[AtinLango]

Now I notice that the rear left side (hub to fender) is a little higher than the rear right side by about 0.75 inch. Just wondering what could have caused this, and any possible solution?

I know we fidgeted with the rear height adjuster a bit while trying to resolve the original problem of rear stuck in L. Could this have caused the height difference?

 

[IndroCruise]

Now I notice that the rear left side (hub to fender) is a little higher than the rear right side by about 0.75 inch. Just wondering what could have caused this, and any possible solution?

I know we fidgeted with the rear height adjuster a bit while trying to resolve the original problem of rear stuck in L. Could this have caused the height difference?

There are a few ideas at this post .....

Props to PADDO's AHC fluid replacement method!

Did my measurements in N mode. 19.5" front and the rears one side is 21" and the other is an inch lower. Do I need to mess with the rear sensor? How full is your gas tank?

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