The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (3 Viewers)

[js47]

Those guys are a couple of bucks each if you can get what’s left of it cleanly out. I have a handful of them on hand for such an event, but have never had to use one. Part No 49189-60010

49189-60010 Genuine Lexus Plug, BLEEDER Suspension

Genuine 49189-60010 Plug, BLEEDER Suspension fits 1998-2021 Lexus LX470, LX570. LexusPartsNow offers 4918960010 for $2.74.

www.lexuspartsnow.com

Thanks Tim, good to know that replacements are easy to come by. But how to get it out in the first place? Plus, the accumulator is still full of fluid.

 

[tjb]

Thanks Tim, good to know that replacements are easy to come by. But how to get it out in the first place? Plus, the accumulator is still full of fluid.

Depends on what you’ve got left to spin out of there. WEAR EYE PROTECTION.

In fact, someone knowledgeable should weigh in on whether this can be safely done. Not sure what the pressures are in that guy.

 

[IndroCruise]

HELP!! I was flushing my AHC today and snapped off the accumulator bleeder.... Will post photos below. No fluid has left the accumulator but I am still in L mode. I wonder if the partial bleeder can handle the pressure?

The system is otherwise in great condition –– globes and shocks replaced by PO at Lexus <40k miles ago, 14+ graduations before the flush. I was not expecting anything to break considering the young age of the system, but I guess the accumulator must be original. Any suggestions for what I should do?

TIA


View attachment 2639527
View attachment 2639528

Late Edit: Labels on pic of Height Control Accumulator were corrected on 22nd May 2021

Deepest sympathy!! This is one of the most frustrating things that can happen on the AHC system. I recently participated in an IH8MUD thread on this problem -- will post the link as soon as I find it again.

Meanwhile, it looks like the bleeder has refused to turn. If so, it means that the thread is frozen/corroded in place. In the closed condition, the blind tip of the bleeder then blocks fluid flow from the Height Control Accumulator from reaching the small bypass hole which allows fluid to exit when the bleeder is opened. The first picture is not exactly the same as the AHC bleeders but it is near enough to visualise what happens when the bleeder is in place. The second picture shows the actual AHC bleeders and caps and part numbers as already mentioned by @tjb

In your case, it does not look like the threaded part of the bleeder has moved at all while you were trying to open it and the bleeder has broken above the thread. No leakage is visible in your pictures. It is highly unlikely that the bleeder remnant in the accumulator will turn, almost impossible for it to be blown out with hydraulic pressure, and it will have to be removed from the accumulator. Removal is quite a process, more about that later.

Note in the hydraulic circuit that the bleeder is on the accumulator side of the solenoid valve and the solenoid valve remains closed unless the ECU tells it to open to assist raising the vehicle, or, when the accumulator is being recharged by the AHC pump. That means that the pressure in the accumulator is "locked in" unless released by operation of the solenoid valve, or, released by opening the bleeder on the accumulator. The accumulator pressure is not released merely by opening the bleeder on any of the 'globes'. The Height Control Accumulator pressure usually recorded by Techstream and other scanners is around 10.5MPa.

If this were my vehicle, I would now raise to HI height and observe whether there is any leakage at the bleeder. It would be good if there is because it would tell me that the bleeder has been loosened a little, meaning that eventual extraction will be easier. However, it is much more likely that there will be no movement and no leakage and that the bleeder is well and truly stuck and that it is not going anywhere any time soon.

If the bleeder is stuck, then I would complete the bleed process but only at the four 'globes'. The vehicle is then driveable. The AHC system will work as it should, unless some air remains in the system. Repeated HI to LO movements and repeated bleeding may help clear remaining air -- this relies on repeated operation of the solenoid valve when the Height Control Accumulator raises the vehicle and is recharged.

I will revert with more about removal of the stuck bleeder as soon as I find the relevant thread rather than type out the whole story again.

The attached document at Page 4 will help you identify the age of the accumulator. The document is not otherwise relevant.

PLEASE WEAR GOOD INDUSTRIAL GRADE EYE PROTECTION WHEN DEALING WITH THE AHC SYSTEM, AND ESPECIALLY WHEN DEALING WITH THIS PROBLEM.

 

[IndroCruise]

Deepest sympathy!! This is one of the most frustrating things that can happen on the AHC system. I recently participated in an IH8MUD thread on this problem -- will post the link as soon as I find it again.

Meanwhile, it looks like the bleeder has refused to turn. If so, it means that the thread is frozen/corroded in place. In the closed condition, the blind tip of the bleeder then blocks fluid flow from the Height Control Accumulator from reaching the small bypass hole which allows fluid to exit when the bleeder is opened. The first picture is not exactly the same as the AHC bleeders but it is near enough to visualise what happens when the bleeder is in place. The second picture shows the actual AHC bleeders and caps and part numbers as already mentioned by @tjb

View attachment 2639649


View attachment 2639650

View attachment 2639666

View attachment 2639679

In your case, it does not look like the threaded part of the bleeder has moved at all while you were trying to open it and the bleeder has broken above the thread. No leakage is visible in your pictures. It is highly unlikely that the bleeder remnant in the accumulator will turn, almost impossible for it to be blown out with hydraulic pressure, and it will have to be removed from the accumulator. Removal is quite a process, more about that later.

Note in the hydraulic circuit that the bleeder is on the accumulator side of the solenoid valve and the solenoid valve remains closed unless the ECU tells it to open to assist raising the vehicle, or, when the accumulator is being recharged by the AHC pump. That means that the pressure in the accumulator is "locked in" unless released by operation of the solenoid valve, or, released by opening the bleeder on the accumulator. The accumulator pressure is not released merely by opening the bleeder on any of the 'globes'. The Height Control Accumulator pressure usually recorded by Techstream and other scanners is around 10.5MPa.

If this were my vehicle, I would now raise to HI height and observe whether there is any leakage at the bleeder. It would be good if there is because it would tell me that the bleeder has been loosened a little, meaning that eventual extraction will be easier. However, it is much more likely that there will be no movement and no leakage and that the bleeder is well and truly stuck and that it is not going anywhere any time soon.

If the bleeder is stuck, then I would complete the bleed process but only at the four 'globes'. The vehicle is then driveable. The AHC system will work as it should, unless some air remains in the system. Repeated HI to LO movements and repeated bleeding may help clear remaining air -- this relies on repeated operation of the solenoid valve when the Height Control Accumulator raises the vehicle and is recharged.

I will revert with more about removal of the stuck bleeder as soon as I find the relevant thread rather than type out the whole story again.

The attached document at Page 4 will help you identify the age of the accumulator. The document is not otherwise relevant.

PLEASE WEAR GOOD INDUSTRIAL GRADE EYE PROTECTION WHEN DEALING WITH THE AHC SYSTEM, AND ESPECIALLY WHEN DEALING WITH THIS PROBLEM.

Hi @js47,

The link below – and the links within this link and the associated attachments may be of assistance.

Removal of Height Control Accumulator? - https://forum.ih8mud.com/threads/removal-of-height-control-accumulator.1243255/#post-13687084

Unfortunately, today there is no time to edit this lengthy information into a shorter form for you.

Basically, my recommendations are

• after checking for leaks and completing the bleed as described in my previous post #183 in this thread today, the vehicle can be driven,

• the Height Control Accumulator can be removed from the vehicle at a convenient time,

• the solenoid valve on the accumulator should be operated by connection to a battery to release the internal pressure under safe conditions with the accumulator secured to the vehicle or to a bench and covered, all done in way that there is no chance of the accumulator becoming a projectile when pressure is released and with appropriate industrial grade personal protective equipment so that there is no chance of high pressure fluid causing eye damage or skin penetration.

• the broken bleeder valve should carefully and safely removed using an EZ-OUT or similar or better procedure.

Unless very comfortable with the procedures, risks and safety precautions involved, this work should be carried out by a workshop with hydraulic capabilities and experience.

Alternatively, the Height Control Accumulator could be replaced with a new or secondhand unit.

@Budmac is tagged in case he can add something from his experience with a similar problem in February 2021 and @suprarx7nut and @2001LC are tagged for their general knowledge.

Hopefully this gives you a start in finding a useful and safe way forward.

 

[js47]

@IndroCruise thank you so much for your replies here and on other threads! No need to edit anything down, I read it all. I am very impressed by your deep knowledge of the system.

My accumulator says 8819 so it is indeed original.

What I Have Done Thus Far:

1. I proceeded normally with the flush as if nothing had gone wrong during the accumulator bleeding step. I bled one front and one rear globe, then raised to N. Then I bled a small amount from each of the four globes until fresh fluid came out.
2. I raised the suspension to H as per @IndroCruise’s recommendation and left it that way overnight. As of this morning, no fluid has bypassed what remains of the bleeder. My broken bleeder looks slightly different from the photos posted above as the threads go all the way to the hex head, but I do not think any of the load-bearing threads were compromised. I will post higher quality closeups of my broken bleeder at the end of this post.

Question: I have been reading the “New Car Features” PDF (New Car Features > Chassis > Suspension > AHC) linked to in one of @IndroCruise ’s excellent earlier posts and it seems that when raising the vehicle from L to N or N to H, all of the fluid in the accumulator gets directed to the four globes. Therefore, given that I raised the suspension to N as part of the normal bleeding procedure, wouldn’t the accumulator now be full of exclusively fresh fluid? And all of the old fluid that was in the accumulator was removed from the system when I rebled all four globes while in N?

The only thing that makes me question that assumption is that it does not jive with the recommended bleeding procedure from Post #1 in this thread. So either the accumulator bleeding step is slightly redundant, or I am not understanding something properly. A screenshot of the relevant pages is below.

My Current (Tentative) Plan:

1. Re-bleed the four globes now that I am in H mode, just to be 100% sure that 100% of the old fluid from the unbled accumulator has been purged from the system. I do not expect any old fluid to come out, this is just to make sure.
2. Rattle can the exposed steel of the broken bleeder that is stuck in the accumulator to prevent any further corrosion.
3. Proceed to live my life normally with no accumulator bleeder.
4. If a time presents itself in the future to replace the accumulator, I will do it via the @YvesNL method. Really not sure when that would be though — are accumulator failures common? A failure is the only situation I can imagine where I would replace the accumulator, and I don’t foresee any situation where I would replace only the bleeder.

Thoughts on this plan? Do you see any major downsides to being without an accumulator bleeder for, potentially, the rest of time?

What happens in the unlikely scenario where the bleeder remnant blows out of the accumulator? Theoretically I feel like the system will operate as normal, just using the pump for all height adjustments? Or would the fluid still be pumped via the accumulator and therefore it would be pumped through the bleeder hole and out of the system, so I would just quickly run out of fluid? If I notice in time to unplug or cut the wiring harness to the accumulator solenoid might the system just operate normally, only using exclusively the pump?

 

[saudi]

@IndroCruise thank you so much for your replies here and on other threads! No need to edit anything down, I read it all. I am very impressed by your deep knowledge of the system.

My accumulator says 8819 so it is indeed original.

What I Have Done Thus Far:

1. I proceeded normally with the flush as if nothing had gone wrong during the accumulator bleeding step. I bled one front and one rear globe, then raised to N. Then I bled a small amount from each of the four globes until fresh fluid came out.
2. I raised the suspension to H as per @IndroCruise’s recommendation and left it that way overnight. As of this morning, no fluid has bypassed what remains of the bleeder. My broken bleeder looks slightly different from the photos posted above as the threads go all the way to the hex head, but I do not think any of the load-bearing threads were compromised. I will post higher quality closeups of my broken bleeder at the end of this post.

Question: I have been reading the “New Car Features” PDF (New Car Features > Chassis > Suspension > AHC) linked to in one of @IndroCruise ’s excellent earlier posts and it seems that when raising the vehicle from L to N or N to H, all of the fluid in the accumulator gets directed to the four globes. Therefore, given that I raised the suspension to N as part of the normal bleeding procedure, wouldn’t the accumulator now be full of exclusively fresh fluid? And all of the old fluid that was in the accumulator was removed from the system when I rebled all four globes while in N?

The only thing that makes me question that assumption is that it does not jive with the recommended bleeding procedure from Post #1 in this thread. So either the accumulator bleeding step is slightly redundant, or I am not understanding something properly. A screenshot of the relevant pages is below.

View attachment 2640188


My Current (Tentative) Plan:

1. Re-bleed the four globes now that I am in H mode, just to be 100% sure that 100% of the old fluid from the unbled accumulator has been purged from the system. I do not expect any old fluid to come out, this is just to make sure.
2. Rattle can the exposed steel of the broken bleeder that is stuck in the accumulator to prevent any further corrosion.
3. Proceed to live my life normally with no accumulator bleeder.
4. If a time presents itself in the future to replace the accumulator, I will do it via the @YvesNL method. Really not sure when that would be though — are accumulator failures common? A failure is the only situation I can imagine where I would replace the accumulator, and I don’t foresee any situation where I would replace only the bleeder.

Thoughts on this plan? Do you see any major downsides to being without an accumulator bleeder for, potentially, the rest of time?

What happens in the unlikely scenario where the bleeder remnant blows out of the accumulator? Theoretically I feel like the system will operate as normal, just using the pump for all height adjustments? Or would the fluid still be pumped via the accumulator and therefore it would be pumped through the bleeder hole and out of the system, so I would just quickly run out of fluid? If I notice in time to unplug or cut the wiring harness to the accumulator solenoid might the system just operate normally, only using exclusively the pump?

View attachment 2640194
View attachment 2640205

 

[saudi]

These are my readings if I alter the sensor n reading to zero won’t the height be all over the place if my heights are correct now ( they aren’t)

 

[IndroCruise]

@IndroCruise thank you so much for your replies here and on other threads! No need to edit anything down, I read it all. I am very impressed by your deep knowledge of the system.

My accumulator says 8819 so it is indeed original.

What I Have Done Thus Far:

1. I proceeded normally with the flush as if nothing had gone wrong during the accumulator bleeding step. I bled one front and one rear globe, then raised to N. Then I bled a small amount from each of the four globes until fresh fluid came out.
2. I raised the suspension to H as per @IndroCruise’s recommendation and left it that way overnight. As of this morning, no fluid has bypassed what remains of the bleeder. My broken bleeder looks slightly different from the photos posted above as the threads go all the way to the hex head, but I do not think any of the load-bearing threads were compromised. I will post higher quality closeups of my broken bleeder at the end of this post.

Question: I have been reading the “New Car Features” PDF (New Car Features > Chassis > Suspension > AHC) linked to in one of @IndroCruise ’s excellent earlier posts and it seems that when raising the vehicle from L to N or N to H, all of the fluid in the accumulator gets directed to the four globes. Therefore, given that I raised the suspension to N as part of the normal bleeding procedure, wouldn’t the accumulator now be full of exclusively fresh fluid? And all of the old fluid that was in the accumulator was removed from the system when I rebled all four globes while in N?

The only thing that makes me question that assumption is that it does not jive with the recommended bleeding procedure from Post #1 in this thread. So either the accumulator bleeding step is slightly redundant, or I am not understanding something properly. A screenshot of the relevant pages is below.

View attachment 2640188


My Current (Tentative) Plan:

1. Re-bleed the four globes now that I am in H mode, just to be 100% sure that 100% of the old fluid from the unbled accumulator has been purged from the system. I do not expect any old fluid to come out, this is just to make sure.
2. Rattle can the exposed steel of the broken bleeder that is stuck in the accumulator to prevent any further corrosion.
3. Proceed to live my life normally with no accumulator bleeder.
4. If a time presents itself in the future to replace the accumulator, I will do it via the @YvesNL method. Really not sure when that would be though — are accumulator failures common? A failure is the only situation I can imagine where I would replace the accumulator, and I don’t foresee any situation where I would replace only the bleeder.

Thoughts on this plan? Do you see any major downsides to being without an accumulator bleeder for, potentially, the rest of time?

What happens in the unlikely scenario where the bleeder remnant blows out of the accumulator? Theoretically I feel like the system will operate as normal, just using the pump for all height adjustments? Or would the fluid still be pumped via the accumulator and therefore it would be pumped through the bleeder hole and out of the system, so I would just quickly run out of fluid? If I notice in time to unplug or cut the wiring harness to the accumulator solenoid might the system just operate normally, only using exclusively the pump?

View attachment 2640194
View attachment 2640205

Responses to @js47 questions and comments are interpolated below .....

Question by @js47:

I have been reading the “New Car Features” PDF (LC100 Workshop Manual - https://lc100e.github.io/ -- New Car Features > Chassis > Suspension > AHC) linked to in one of @IndroCruise ’s excellent earlier posts and it seems that when raising the vehicle from L to N or N to H, all of the fluid in the accumulator gets directed to the four globes. Therefore, given that I raised the suspension to N as part of the normal bleeding procedure, wouldn’t the accumulator now be full of exclusively fresh fluid? And all of the old fluid that was in the accumulator was removed from the system when I rebled all four globes while in N?

Yes -- if your 22+ year old Height Control Accumulator (HCA) and its solenoid valve and also the AHC Pump are still in close-to-new condition, then the HCA could be expected to have discharged completely in the LO > N raise and then to have been recharged by the AHC Pump. The pump would run for 15 seconds (per FSM) but maybe up to 30 (?) seconds (depending on the condition of both the pump and the HCA) after the vehicle has arrived at N height, and eventually shows approximately 10.5MPa on Techstream or other scanner when the pump stops. However, the internal condition of the HCA piston and actual remaining nitrogen gas pressure behind the piston within the HCA are unknown. They may be adequate but not perfect. Likewise, the AHC Pump also may be adequate but not perfect. The actual extent to which the HCA truly has discharged its full volume is difficult to discern. Usually, the AHC Pump comes to the rescue and assists the raise LO > N (or to HI) -- and the pump usually can be heard to start before the raise is completed. Suspicions about the HCA might be aroused if the raise was slow -- although slow raise can be the result of several different causes including gear pump components or partially blocked strainers inside the pump assembly, overweight vehicle, worn or binding mechanical suspension parts, etc, etc. The situation is not necessarily fatal but it is the reason why multiple cycles are suggested in my earlier post. This may never achieve complete fluid replacement but does aim to achieve massive dilution of any old fluid and any air remaining. The reference to "air" is meant to include air dissolved in fluid (per Kelvin's Law) as well as physical air bubbles.

The only thing that makes me question that assumption is that it does not jive with the recommended bleeding procedure from Post #1 in this thread. So either the accumulator bleeding step is slightly redundant, or I am not understanding something properly.

The mentioned understanding is sound and the assumption might be true in perfect conditions. However, the relevant AHC components are not new -- LC100/LX470 vehicles are now 14 to 22 years old. The AHC system has closed ends at the Shock Absorbers and it is never possible to completely flush out old AHC Fluid from the entire system and replace cleanly with all new fluid by the bleeding process. So the more fluid exit points the better for maximising fluid replacement and minimising (but never quite eliminating) pollution with remaining old fluid carrying air (bubbles or dissolved) within the system. Additionally, the amount of fluid discharged through the Height Control Accumulator (HCA) bleeder (when that is possible!) does give some useful indication of the condition of the HCA. So I remain a strong supporter of of the procedure described by @LndXrsr in Post #1 and onwards in this thread and by his predecessors in earlier threads -- or any variation which is even more efficient at maximising fluid replacement. I see the procedure involving the HCA bleed as cautious and thorough rather than redundant. As discussed later, if the HCA bleeder is broken, then one option IS to retain the damaged HCA and make do without bleeding at this point despite the disadvantages, potentially indefinitely with care and good monitoring, unless and until some serious malfunction develops in the HCA.

Current (Tentative) Plan by @js47

1. Re-bleed the four globes now that I am in H mode, just to be 100% sure that 100% of the old fluid from the unbled accumulator has been purged from the system. I do not expect any old fluid to come out, this is just to make sure.
2. Rattle can the exposed steel of the broken bleeder that is stuck in the accumulator to prevent any further corrosion.
3. Proceed to live my life normally with no accumulator bleeder.
4. If a time presents itself in the future to replace the accumulator, I will do it via the @YvesNL method. Really not sure when that would be though — are accumulator failures common? A failure is the only situation I can imagine where I would replace the accumulator, and I don’t foresee any situation where I would replace only the bleeder.

Thoughts on this plan? Do you see any major downsides to being without an accumulator bleeder for, potentially, the rest of time?

This is a reasonable and rational plan. However, there is not much point in focusing on HI mode. As discussed above, there is nothing to guarantee a 100% purge from from a single movement. Instead, consider multiple raise/lower/bleed cycles using the recommended bleed method -- with no short-cuts other than the omission of the Height Control Accumulator (HCA) bleed due only to the broken bleed valve. Suggest be guided by exiting fluid quality in the normal way and by the ride quality of the vehicle. If in doubt, N > LO > N and bleed again -- and N > LO > N and bleed again ....

While the circumstances are quite different, the long thread below leading up to Post #243 by @aharlan001 shows how frustrating bleeding can be and the persistence which may be required:

AHC Inop after fluid change 2007 lx C1751 and C1762 - https://forum.ih8mud.com/threads/ahc-inop-after-fluid-change-2007-lx-c1751-and-c1762.1233088/page-13#post-13517321

The Height Control Accumulator (HCA) with broken bleed valve could remain on the vehicle indefinitely unless or until some HCA malfunction emerges which mandates further action. Active Height Control (AHC) and Toyota Electronic Modulated Suspension (TEMS) would continue to operate normally in the absence of other faults. Monitoring of the action of the HCA could include physically listening/feeling the operation of its solenoid valve in its correct sequence during a raise, and observing whether that corresponds to the relevant signal from the ECU which can be seen on Techstream or other scanner -- look for "SLAC" (Solenoid Accumulator) on the usual readout page during a raise. Monitoring raise times also may be useful despite the multiple causes mentioned earlier. Testing the solenoid valve also is a useful indicator -- see LC100 Workshop Manual - https://lc100e.github.io/, then Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS > C1731 to C1736 (Control Valve Solenoid and Accumulator Solenoid Circuit at Page DI-239 and onwards including the ACTIVE TEST procedure on Page DI-241, and the electrical continuity test at Page DI-242).

What happens in the unlikely scenario where the bleeder remnant blows out of the accumulator? Theoretically I feel like the system will operate as normal, just using the pump for all height adjustments? Or would the fluid still be pumped via the accumulator and therefore it would be pumped through the bleeder hole and out of the system, so I would just quickly run out of fluid? If I notice in time to unplug or cut the wiring harness to the accumulator solenoid might the system just operate normally, only using exclusively the pump?

Your Height Control Accumulator (HCA) bleeder remnant is well-rusted and locked in place, no less so that when the bleeder was intact. It is no more likely to blow out now than it was before removal was attempted. Suggest look again at the diagram of the HCA cross-section. In the unlikely event that the bleeder did blow out, then the HCA would discharge to atmosphere, meaning, spray AHC fluid wildly under the vehicle. The AHC Pump may start as a result of the ECU recognising a pressure drop in the HCA. If so, the fluid pumped into the HCA also would short-circuit immediately to atmosphere through the bleeder hole. The vehicle would not raise. I leave it to you to inspect the various fault conditions which might then arise and ascertain whether the AHC Pump would stop before it runs dry (when it will stop): see https://lc100e.github.io/, then Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS.

Could the Height Control Accumulator (HCA) be isolated from the AHC system by unplugging the electrical connector at the rear of the HCA? I don't know the answer to that. I suspect that because the HCA feeds fluid and pressure to to the Control Valve Assembly (which in turn directs fluid to the Front and Rear Levelling Valves), disconnection of the HCA may result in multiple faults (and the relevant DTC's) and may result in the 'fail safe mode' specified at Page DI-239. This involves the ECU prohibiting height control and fixing the damping force at sports mode. However, nothing prevents you trying this disconnection immediately. If the action does generate faults, then these will be cleared immediately when the connector is replaced and the DTC's are cleared from the record on Techstream or other scanner. If no such faults nor 'fail safe mode' occurs, then you will have found something of value and interest to owners of LC100/LX470 vehicles with AHC! Please let us know what you discover .....

SAFETY REMINDERS:

Wear Industrial strength eye protection and skin protection whenever dealing with hydraulic fluids under pressure. In the absence of relevant personal knowledge and competencies, always obtain qualified workshop help.

Use locked vehicle stands under chassis rails whenever a person works under a vehicle on the AHC system to ensure that the vehicle body cannot descend onto a human body

 

[saudi]

I initially put this in the Definitive list of AHC maintenance items thread, but at almost 800 posts long and growing, it's going to get buried and the thread itself is very unwieldy.

In an attempt to make as focused a summary as possible, I present "The ABCs of AHC." It's intended as a comprehensive, linear checklist for anyone who needs to get their AHC back into factory tune. Information gathered from as many sources as I could find on this forum; I take no credit for developing any of this, just bringing it all together as much as possible. Special shout outs to @PADDO, @uHu, @IndroCruise, @PabloCruise and @2001LC for many of the details, specs, and procedures I've included in here. Feedback more than welcome, will make edits as appropriate based on what I hear.


A - Assess: Figure out where you’re starting from

1. Wheels on level ground, no ramps, jacks, or stands needed for parts A, B, or C. DO NOT PUT YOURSELF PHYSICALLY UNDER THE VEHICLE FOR ANY OF THIS.
2. Get your rig loaded/unloaded to what is “typical” for your use.
   • FSM calls for no driver or passengers, full tank of fuel.
3. Measure ride height at all 4 corners from center of wheel cap vertically to fender lip on a level surface
   • Front OEM: 19.75” (50.2cm)
   • Rear OEM: 20.5” (52.1cm)
   • Drive a bit, then park in the same level place. Take 3-5 measurements and get a mean or median.
4. Measure difference in AHC tank level between H and L suspension heights
   • >7 graduations acceptable, 14 graduations new from factory
   • Need to replace globes/spheres if <7 after parts A, B, and C are complete.
   • Backlight AHC fluid tank with a light to help see fluid level
   • Again, 3-5 measurements and take a mean or median value
5. Measure your front/rear pressures, accumulator pressure, and sensor heights using Techstreamand a Mini-VCI cable, a manual inline gauge, or an advanced OBDII reader (iCarsoft, TYT II, OBDLink, VGate, etc.)
   • Front spec: 6.9MPa +/- 0.5
   • Rear spec: 5.6-6.7MPa
   • Accumulator spec: 10-10.6MPa
   • Start car, connect Techstream, make sure you choose your exact model, not the default Land Cruiser with no AHC installed
   • Open AHC channel and select "data list" to monitor values
   • Cycle from N to L to N again. Take a screenshot of your values. There are Front R and Front L height sensors but only one rear sensor for pressure and height. May need to disconnect the AHC temp sensor to get accurate rear readings per FSM.
   • Again, 3-5 measurements and take a mean or median value for each data point.

B - Bleed: Flush out the old AHC fluid

1. Procure three 1L bottles of OEM AHC fluid (08886-81221)
2. Put AHC in Low, turn engine off
3. Suck all old fluid out of AHC tank (~1L if level was between Max/Min at N height)
4. Pour in new fluid to top of tank (~2.5L)
5. Bleed accumulator until fluid stops (long cylinder on left side frame rail) (~300mL, 10mm wrench)
   • Bleeder torque spec: 62 in-lbf (5.5 ft-lbf, 7.5 N-m)
6. Bleed one front and one rear damper (globe unit) until both front and rear are on the bump stops and fluid stops flowing (~300-400mL each)
   • Bleeder torque spec: 73 in-lbf (6.0 ft-lbf, 8.1 N-m)
   • Careful, as the car will lower significantly during this process. Don't put yourself under the vehicle!
7. Start car, put AHC in Neutral until pump stops, turn off again
8. Bleed the remaining front and rear dampers on the other side of the car for just a second until fresh fluid and no air comes out (~50mL each)
9. Start car, cycle to AHC to L then back to N
10. Top off AHC fluid in the reservoir. Should be between Max/Min at N height.
11. Recheck graduations in the tank as described in step A2. May see some improvement, may not.

C – Crank/Check: Adjust the side-to-side height and neutral pressures front/rear

1. Remeasure your ride heights as in Step A1. Measure twice, cut once.
2. Fix any left-to-right ride height imbalance, i.e. lean. This is commonly called “cross-leveling” throughout this thread. This is done entirely by adjusting the front torsion bars (TBs), not height sensors.
   • Tighten (CW) a TB nut to raise a low side, loosen (CCW) to lower a high side. 30mm wrench/socket
   • Mark your TB nuts (permanent or paint marker) so that you don’t lose track of where a full turn is
   • Place AHC in H to lessen pressure on TBs and make turning easier. Put back to N for measurements.
   • ~1/8” correction in left-to-right height imbalance per full turn of a TB nut
   • Best to turn TBs equal amounts in opposite directions until level
   • Drive a bit, repeat, measure until satisfied with left and right ride heights being equal
3. Adjust the three ride height sensors as needed to achieve as close to 0mm on all values at N in Techstream.
   • Engine off, ignition on. Monitor changes in real time on Techstream.
   • Raise: Shorten heim joint (the adjustable threaded rod) or move the top of the joint up in its slider
   • Lower: Lengthen heim joint or move the top of the joint down in its slider
   • Rear sensor only has a slider
   • <10mm (0.3-0.4in) between the two most discrepant sensors is acceptable
   • Recheck ride height as in step A2. If all sensors at/near 0mm, ride height should be very close to OEM spec, otherwise sensor(s) may be malfunctioning.
4. Adjust front N height pressures by cranking the TBs
   • Place AHC in H to lessen pressure on TBs and make turning easier
   • Lower pressures: tighten (CW) both TBs the same amount
   • Raise pressures: loosen (CCW) both TBs the same amount
   • ~0.2MPa change in pressure per full turn of a TB nut
   • Cycle H to L to N. Recheck pressures as in step A5.
5. Check rear N height pressure
   • OEM specs in step A5
   • May need to disconnect the AHC temp sensor to get accurate rear readings per FSM (Decreases pressures ~0.8-1). Try it both ways.
   • Rear pressures can be changed with new springs (OEM or King), spacers, airbags, or rear sensor height adjustments (but this last one also change the height of your rear and the car’s rake front to back).
6. Check graduations in the tank as described in step A2. Again, may see some improvement, may not.

Good luck! Hope folks find this a helpful all-in-one reference for tackling their AHC. Maybe it will prevent a few of you from ripping out a great system. Save the AHCs!

im so confused here , i know yo adjust the torsen bars to level car, but dont you then adjust the sensors to get ride height?. if you just adjust to get 0 n wont height be all over the place.my fluid is all new 15 on graduation test it does need to be levelled slightly , but my front n readings are fr 13.4 fl -17.4.HELP

 

[IndroCruise]

These are my readings if I alter the sensor n reading to zero won’t the height be all over the place if my heights are correct now ( they aren’t)

View attachment 2640281

Late edit: Pictures inserted, Front and Rear Sensors

Second request in Post #189 in this thread also is noted in which @saudi asked:

im so confused here , i know yo adjust the torsen bars to level car, but dont you then adjust the sensors to get ride height?. if you just adjust to get 0 n wont height be all over the place.my fluid is all new 15 on graduation test it does need to be levelled slightly , but my front n readings are fr 13.4 and fl -17.4.HELP

The frustrations are understood and respected and your Techstream readout is very strange indeed. Maybe the following notes will help you and maybe help others with similar questions:

• All three Height Control Sensors and their linkages, electrical connectors and harnesses must be confirmed to be in reliable condition and capable of performing as intended. If in doubt, removal, dis-assembly, cleaning, electrical testing are essential. Replacement of old Sensors may be the best course of action.

• As you already recognise, ‘cross-leveling’ at the Front must be done properly at the start. All height adjustments of any kind are done with vehicle on a level surface, no driver nor passengers nor any other variable load on board, except fuel which should be full. It is vital to equalise static front hub-to-fender heights, with the vehicle set at “N”height, using a tape-measure (nothing to do with Techstream or other scanners), must be done before anything else, with Torsion Bar adjusters only, with engine and AHC “OFF” per attached FSM extract, within 10 millimetres (0.39 inches) side-to- side difference or better, actual measurements do not matter, just equalise Front Right and Front Left in this step – otherwise all else that follows will be built on a mistake and ongoing frustration is guaranteed,

• With ‘cross-levelling’ correct, move to adjusting ‘operating heights’ (also called ‘ride heights’) of the vehicle. The relevant targets for ‘ride heights’ for a non-lifted vehicle are the well-known IH8MUD recommendations: Front 19.75 inches or 500 millimetres on both sides; Rear 20.50 inches or 520 millimetres on both sides These are reliable approximations of the more detailed height measurements prescribed in the FSM. All measurements are by tape-measure, with the vehicle set at “N”height, nothing to do with Techstream or other scanners – these are not yet required. The Front heights are set correctly (or nearly correct) first. Setting Rear height comes later and ‘fine tuning’ Front and Rear also comes later.

• The easiest way to raise height in a controlled manner is to use the “ACTIVE TEST” per FSM, or, see last page of second attachment (bridging relevant pins at DLC1 is easier than at DLC3). Raise the front to the desired hub-to-fender distance. Maybe raise a little (or lower), measure with tape-measure, raise again until correct tape-measured front hub-to-fender height is reached. When satisfied, stop and switch engine “OFF. The vehicle will stay at this tape-measured height -- unless there is a problem with, say, internal leakage at the Levelling Valves inside the Control Valve Assembly or with the Return Valve at the AHC Pump, or some other unusual problem, or unless the engine is switched “ON” and the AHC is allowed to self-level. So engine and AHC remain ‘’OFF” for now. Techstream or other scanner are not required yet.

• Alternatively, (and many people do it this way), use front Height Control Sensor slide adjusters (easier than heim bolts) to cause the Front to raise (or lower), maybe in a couple of steps, until the required front hub-to-fender tape-measured height is achieved. For safety, move both sliders a little with the engine “OFF”, then restart engine to allow vehicle and AHC to find the new height, drive around the block if necessary, then tape-measure the front hub-to-fender heights again while engine and AHC are still “ON”. Repeat until satisfied that the required tape-measured hub-to-fender 'ride height' has been achieved, then switch the engine “OFF”. As above, the vehicle will stay at this height unless something is very wrong in the system or unless the vehicle is re-started and moved, causing the system to attempt to self-level unhelpfully.

• FOR PERSONAL SAFETY, AVOID ADJUSTING HEIGHT CONTROL SENSORS WITH HEAD OR HANDS OR OTHER BODY PARTS IN THE WHEEL ARCHES OR UNDER THE BODY WHILE THE ENGINE IS “ON” AND THE AHC SYSTEM IS ACTIVE. A MISTAKE OR UNINTENDED MOVEMENT OF THE VEHICLE BODY ONTO THE HUMAN BODY WOULD EASILY CAUSE SERIOUS INJURY.

• @PADDO describes a safe method at this Post #2 in this thread:
  High as a kite, hard as a rock! (Yes AHC again...) - https://forum.ih8mud.com/threads/high-as-a-kite-hard-as-a-rock-yes-ahc-again.1119157/#post-12149330

• When the vehicle is stationary, the Gate Valves in the Control Valve Assembly are open and Front Right and Front Left AHC pressures are equal. The Front Right and Front Left hub-to-fender heights CANNOT be set differently by using the Right and Left front Height Control Sensor slide adjusters or heim adjuster bolts. [Note: The LC100/LX470 AHC system is a two-channel system capable of raising/lowering Front and Rear of the vehicle. It cannot raise/lower each of the four corners independently – this would require a four-channel system]. So no need to try too hard for exactly equal Height Control Sensor movements nor even bother with Techstream at this stage because Sensor differences cannot cause different 'ride heights' on either side. The aim is simply to achieve the required tape-measured Front hub-to-fender 'ride height'. The engine is still "OFF". Techstream or other scanner is not required at this stage.

• Now double-check that ‘cross-level’ is still correct and has not been disturbed. Some variation can occur, mainly due to wear or differences in mechanical components of the suspension. Readjust ‘cross-level’ if necessary, with engine still “OFF”, using only Torsion Bar adjusters.

• The engine and AHC system remains “OFF” until the relevant step later in the sequence below.

• When satisfied that the vehicle has been correctly ‘cross-levelled’ at the Front AND when satisfied that Front ‘ride height’ is now correct, the next aim is to set the Front Height Control Sensors to read zero +/- 5 millimetre or +/- 0.20 inches at this ‘ride height’.

• The AHC system is designed to self-level the vehicle at the ‘ride height corresponding to “N” at height select switch on the centre console. The Front hub-to-fender height has now been established in the foregoing procedure and the vehicle is now sitting at the correct Front hub-to-fender 'ride height' for “N”. If the centre console switch is set to “LO” or to “HI”, then the ECU will choose the heights that correspond to those settings. It is not necessary make further adjustments for “LO” or “HI” height selections. [More detail on the operation of the AHC system and the role of the Height Control Sensors has been written up in a different thread for a different purpose but may assist with understanding – see Ahc problems. - https://forum.ih8mud.com/threads/ahc-problems.1242268/#post-13722174 ]

• Anyway, now is the time to break out Techstream or other scanner and connect to the vehicle with the Ignition Key “ON” but DO NOT start the engine as this would cause the AHC ECU to attempt an unwanted self-levelling effort. Now read both Front Height Control Sensor readings on Techstream or other scanner WITHOUT starting the engine.

• Now move both Front Height Control Sensor slider adjusters WITHOUT starting the engine until the reading is as close as possible to Zero +/- 5 millimetre or +/- 0.20 inches. The heim threaded bolt can be used for fine adjustment but be aware that this is very fiddly.

• When satisfied, tighten all lock-nuts. Start the vehicle engine, test drive around the block until the suspension settles, then re-check all tape-measurements and also the Techstream readout and make such further adjustments as may be necessary. Some iterations and fine tuning should be expected.

• If all has gone well, at this point the vehicle has been front ‘cross levelled’, front ‘ride height’ at “N” have been set, and the Front Height Control Sensors are set correctly to cause the AHC to self-level the Front to the correct Front hub-to-fender height, with Techstream readings close to Zero +/- 5 millimetre or +/- 0.20 inches

• If the vehicle then fails to self-level at the correct tape-measured front hub-to-fender ‘ride heights and near-zero Sensor readings, then there are problems elsewhere. These may be resolved when the Rear settings are correctly adjusted, or ‘cross levelling’ may be incorrect, or there are one or more faulty Height Control Sensors, linkages, connectors or harness.

• Conduct a similar process to achieve correct Rear hub-to-fender ‘ride height’ and to correctly set the single Rear Height Control Sensor. This task is simpler but the Rear Sensor is less accessible. It is mounted on chassis cross-member in front of the rear diff and connects to the Left Rear Upper Control Arm.

• AGAIN FOR PERSONAL SAFETY, AVOID ADJUSTING HEIGHT CONTROL SENSORS WITH HEAD OR HANDS OR OTHER BODY PARTS UNDER THE BODY WHILE THE ENGINE IS “ON” AND THE AHC SYSTEM IS ACTIVE. A MISTAKE OR UNINTENDED MOVEMENT OF THE VEHICLE BODY ONTO THE HUMAN BODY COULD EASILY CAUSE SERIOUS INJURY. USE LOCKED STANDS UNDER THE CHASSIS TO RESTRICT ANY UNPLANNED MOVEMENT AND FOR PERSONAL PROTECTION.

• When Front and Rear Heights are correct, AHC Neutral Pressures can be measured correctly and compared with FSM specifications – wrong heights means misleading AHC Neutral Pressure results.

• When Front and Rear Heights are correct AND AHC Neutral Pressures also are correct, a correct reading of the difference in the levels of the fluid in the AHC Tank between “LO” and “HI” can be taken to indicate overall globe condition – wrong AHC pressures means misleading results in this test.

Some comments on @saudi data in Post #187:

Front Right Height Control Sensor: +13.4 millimetres (from Techstream)
Front Left Height Control Sensor: -17.4 millimetres (from Techstream)
Rear Height Control Sensor: -2.6 millimetres (from Techstream -- there is only one Rear Sensor)

Actual Sensor differences on @saudi vehicle:

Difference, Right Front to Left Front: 30.8 millimetres
Difference, Right Front to Rear: 16.0 millimetres
Difference, Left Front to Rear: 14.8 millimetres

Factory Service Manual (FSM) specification for Height Control Sensor readings at "N":

zero +/- 5 millimetres or +/- 0.20 inches

Ride quality is not reported for @saudi vehicle – essential information for diagnosis and explanation.

Tape measurements at all four wheels of hub-to-fender ‘Ride heights’ at “N” setting are not reported for @saudi vehicle – essential information for diagnosis and explanation.

Additional Techstream information provided for @saudi vehicle:

Front AHC pressure: 6.1 Mpa -- this is a little low
Rear AHC pressure: 2.4 MPa -- this is incredibly low? What are rear hub-to-fender tape measurements?
Accumulator pressure: 10.6 Mpa – normal

FSM specifications for AHC Neutral Pressures at "N" height is found at https://lc100e.github.io/manual/
then tab Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM (IFS) > ON-VEHICLE INSPECTION

Steering angle: -258.75 degrees – very unusual -- with steering straight ahead this should be close to zero, greater than about 36 degrees will affect Gate Valve operation in the Control Valve Assembly and cause ride quality differences in Left and Right turns due to different operation of the Damping Force Control Actuators on either side of the vehicle. See https://lc100e.github.io/manual/
then tab Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > C1781

The huge differences in the @saudi Height Control Sensor readings reported in Techstream are a worry. Such differences are only possible when

• there is one or more faulty Sensors or damage to mechanical linkages, electrical connectors or harness (Special Note: These faults may not generate a DTC code), or,

• new or secondhand Sensors in proven fault-free, good electrical and mechanical condition have been installed and now require adjustment, or,

• cross-levelling is incorrect, or

• there have been previous unsuccessful attempts to adjust existing Height Control Sensors which have resulted in frustration.

Such large differences may also cause the ECU to place the AHC system into one of several ‘fail safe modes’ with consequences for poor ride quality (no variable damping by TEMS) and limited or no AHC height operation.

 

[saudi]

Second request in Post #189 in this thread also is noted in which @saudi asked:

im so confused here , i know yo adjust the torsen bars to level car, but dont you then adjust the sensors to get ride height?. if you just adjust to get 0 n wont height be all over the place.my fluid is all new 15 on graduation test it does need to be levelled slightly , but my front n readings are fr 13.4 and fl -17.4.HELP

The frustrations are understood and respected and your Techstream readout is very strange indeed. Maybe the following notes will help you and maybe help others with similar questions:

• All three Height Control Sensors and their linkages, electrical connectors and harnesses must be confirmed to be in reliable condition and capable of performing as intended. If in doubt, removal, dis-assembly, cleaning, electrical testing are essential. Replacement of old Sensors may be the best course of action.

• As you already recognise, ‘cross-leveling’ at the Front must be done properly at the start. All height adjustments of any kind are done with vehicle on a level surface, no driver nor passengers nor any other variable load on board, except fuel which should be full. It is vital to equalise static front hub-to-fender heights, with the vehicle set at “N”height, using a tape-measure (nothing to do with Techstream or other scanners), must be done before anything else, with Torsion Bar adjusters only, with engine and AHC “OFF” per attached FSM extract, within 10 millimetres (0.39 inches) side-to- side difference or better, actual measurements do not matter, just equalise Front Right and Front Left in this step – otherwise all else that follows will be built on a mistake and ongoing frustration is guaranteed,

• With ‘cross-levelling’ correct, move to adjusting ‘operating heights’ (also called ‘ride heights’) of the vehicle. The relevant targets for ‘ride heights’ for a non-lifted vehicle are the well-known IH8MUD recommendations: Front 19.75 inches or 500 millimetres on both sides; Rear 20.50 inches or 520 millimetres on both sides These are reliable approximations of the more detailed height measurements prescribed in the FSM. All measurements are by tape-measure, with the vehicle set at “N”height, nothing to do with Techstream or other scanners – these are not yet required. The Front heights are set correctly (or nearly correct) first – setting Rear height comes later and ‘fine tuning’ Front and Rear also comes later.

• The easiest way to raise height in a controlled manner is to use the “ACTIVE TEST” per FSM or last page of second attachment (bridging relevant pins at DLC1 is easier than at DLC3) to raise the front to the desired hub-to-fender distance. Raise a little (or lower), measure with tape-measure, raise again until correct tape-measured front hub-to-fender height is reached. When satisfied, stop and switch engine “OFF. Unless there is a problem with, say, internal leakage at the Levelling Valves inside the Control Valve Assembly or with the Return Valve at the AHC Pump, or some other unusual problem, or unless the engine is switched “ON” and the AHC is allowed to self-level, the vehicle will stay at this tape-measured height. So engine and AHC remain ‘’OFF” for now. Techstream or other scanner are not required yet.

• Alternatively, (and many people do it this way), use front Height Control Sensor slide adjusters (easier than heim bolts) to cause the Front to raise (or lower), maybe in a couple of steps, until the required front hub-to-fender tape-measured height is achieved. For safety, move both sliders a little with the engine “OFF”, then restart engine to allow vehicle and AHC to find the new height, drive around the block if necessary, then tape-measure the front hub-to-fender heights again while engine and AHC are still “ON”. Repeat until satisfied that the required tape-measured hub-to-fender height has been achieved, then switch the engine “OFF”. As above, the vehicle will stay at this height unless something is very wrong in the system or unless the vehicle is re-started and moved, causing the system to attempt to self-level unhelpfully.

• FOR PERSONAL SAFETY, AVOID ADJUSTING HEIGHT CONTROL SENSORS WITH HEAD OR HANDS OR OTHER BODY PARTS IN THE WHEEL ARCHES OR UNDER THE BODY WHILE THE ENGINE IS “ON” AND THE AHC SYSTEM IS ACTIVE. A MISTAKE OR UNINTENDED MOVEMENT OF THE VEHICLE BODY ONTO THE HUMAN BODY WOULD EASILY CAUSE SERIOUS INJURY.

• @PADDO describes a safe method at this Post #2 in this thread:
  High as a kite, hard as a rock! (Yes AHC again...) - https://forum.ih8mud.com/threads/high-as-a-kite-hard-as-a-rock-yes-ahc-again.1119157/#post-12149330

• Note that when the vehicle is stationary, the Gate Valves in the Control Valve Assembly are open and Front Right and Front Left AHC pressures are equal. The Front Right and Front Left hub-to-fender heights CANNOT be set differently with the Right and Left front Height Control Sensor slide adjusters. [Note: The LC100/LX470 AHC system is a two-channel system capable of raising/lowering Front and Rear of the vehicle. It cannot raise/lower each of the four corners independently – this would require a four-channel system].

• Now double-check that ‘cross-level’ is still correct and has not been disturbed. Some variation can occur, mainly due to wear or differences in mechanical components of the suspension. Readjust ‘cross-level’ if necessary, with engine still “OFF”, using only Torsion Bar adjusters.

• The engine and AHC system remains “OFF” until the relevant step later in the sequence below.

• When satisfied that the vehicle has been correctly ‘cross-levelled’ at the Front AND that Front ‘ride height’ are now correct, the aim now is to set the Front Height Control Sensors to read zero +/- 5 millimetre or +/- 0.20 inches at this ‘ride height’.

• The AHC system is designed to self-level the vehicle at the ‘ride height corresponding to “N” at height select switch on the centre console. The Front hub-to-fender height has now been established in the foregoing procedure and the vehicle is now sitting at the correct Front hub-to-fender height for “N”. If the centre console switch is set to “LO” or to “HI”, then the ECU will choose the heights that correspond to those settings. It is not necessary make further adjustments for “LO” or “HI” height selections. [More detail on the operation of the AHC system and the role of the Height Control Sensors has been written up in a different thread for a different purpose but may assist with understanding – see Ahc problems. - https://forum.ih8mud.com/threads/ahc-problems.1242268/#post-13722174 ]

• Anyway, now is the time to break out Techstream or other scanner and connect to the vehicle with the Ignition Key “ON” but DO NOT start the engine as this would cause the AHC ECU to attempt an unwanted self-levelling effort. Now read both Front Height Control Sensor readings on Techstream or other scanner WITHOUT starting the engine.

• Now move both Front Height Control Sensor slider adjusters WITHOUT starting the engine until the reading is as close as possible to Zero +/- 5 millimetre or +/- 0.20 inches. The heim threaded bolt be used for fine adjustment but be aware that this is very fiddly.

• When satisfied, tighten all lock-nuts. Start the vehicle engine, test drive around the block until the suspension settles, then re-check all tape-measurements and also the Techstream readout and make such further adjustments as may be necessary. Some iterations and fine tuning should be expected.

• If all has gone well, at this point the vehicle has been front ‘cross levelled’, front ‘ride height’ at “N” have been set, and the Front Height Control Sensors are set correctly to cause the AHC to self-level the Front to the correct Front hub-to-fender height, with Techstream readings close to Zero +/- 5 millimetre or +/- 0.20 inches

• If the vehicle then fails to self-level at the correct tape-measured front hub-to-fender ‘ride heights, then there are problems elsewhere. These may be resolved when the Rear settings are correctly adjusted, or ‘cross levelling’ may be incorrect, or there are one or more faulty Height Control Sensors, linkages, connectors or harness.

• Conduct a similar process to achieve correct Rear ‘ride height’ and to correctly set the single Rear Height Control Sensor. This task is simpler but the Rear Sensor is less accessible.

• AGAIN FOR PERSONAL SAFETY, AVOID ADJUSTING HEIGHT CONTROL SENSORS WITH HEAD OR HANDS OR OTHER BODY PARTS UNDER THE BODY WHILE THE ENGINE IS “ON” AND THE AHC SYSTEM IS ACTIVE. A MISTAKE OR UNINTENDED MOVEMENT OF THE VEHICLE BODY ONTO THE HUMAN BODY WOULD EASILY CAUSE SERIOUS INJURY. USE LOCKED STANDS UNDER THE CHASSIS TO RESTRICT ANY UNPLANNED MOVEMENT AND FOR PERSONAL PROTECTION.

• When Front and Rear Heights are correct, AHC Neutral Pressures can be measured correctly and compared with FSM specifications – wrong heights means misleading pressure results.

• When Front and Rear Heights are correct AND AHC Neutral Pressures also are correct, a correct reading of the difference in the levels of the fluid in the AHC Tank between “LO” and “HI” can be taken to indicate overall globe condition – wrong pressures means misleading results in this test.

Some comments on your data:

Front Right Height Control Sensor: +13.4 millimetres (from Techstream)
Front Left Height Control Sensor: -17.4 millimetres (from Techstream)
Rear Height Control Sensor: -2.6 millimetres (from Techsdtream -- there is only one Rear Sensor)

Actual Sensor differences on @saudi vehicle:

Difference, Right Front to Left Front: 30.8 millimetres
Difference, Right Front to Rear: 16.0 millimetres
Difference, Left Front to Rear: 14.8 millimetres

Factory Service Manual (FSM) specification for Height Control Sensor readings at "N":

zero +/- 5 millimetres or +/- 0.20 inches

Ride quality is not reported for @saudi vehicle – essential information for diagnosis and explanation.

Tape measurements at all four wheels of hub-to-fender ‘Ride heights’ at “N” setting are not reported for @saudi vehicle – essential information for diagnosis and explanation.

Additional Techstream information provided for @saudi vehicle:

Front AHC pressure: 6.1 Mpa -- this is a little low
Rear AHC pressure: 2.4 MPa -- this is incredibly low? What are rear hub-to-fender tape measurements?
Accumulator pressure: 10.6 Mpa – normal

FSM specifications for AHC neutral pressures is found at https://lc100e.github.io/manual/
then tab Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM (IFS) > ON-VEHICLE INSPECTION

Steering angle: -258.75 degrees – very unusual -- with steering straight ahead this should be close to zero, greater than about 36 degrees will affect Gate Valve operation in the Control Valve Assembly and cause ride quality differences in Left and Right turns due to different operation of the Damping Force Control Actuators on either side of the vehicle. See https://lc100e.github.io/manual/
then tab Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > C1781

The huge differences in the Height Control Sensor readings reported in Techstream are a worry. Such differences are only possible when

• there is one or more faulty Sensors or damage to mechanical linkages, electrical connectors or harness (Special Note: These faults may not generate a DTC code), or,

• new or secondhand Sensors in proven fault-free, good electrical and mechanical condition have been installed and now require adjustment, or,

• cross-levelling is incorrect, or

• there have been previous unsuccessful attempts to adjust existing Height Control Sensors which have resulted in frustration.

Such large differences may also cause the ECU to place the AHC system into one of several ‘fail safe modes’ with consequences for poor ride quality (no variable damping by TEMS) and limited or no AHC height operation.

Thanks I m a lot clearer amazingly the ahc works ok up down ect and no techstream faults the rear is on king springs and is at 20 inches. I’ve photographed latest techstream nothing has been done yet . It’s funny usa techstream recognises it’s a landcruiser but shows 6 less ecu ahc being one of them. But I’ve now got euro techstream and all ok so I assume as uk landcruiser is an Amazon (uk only) but is spec wise Lexus 470 is

 

[saudi]

Late edit: Pictures inserted, Front and Rear Sensors

Second request in Post #189 in this thread also is noted in which @saudi asked:

im so confused here , i know yo adjust the torsen bars to level car, but dont you then adjust the sensors to get ride height?. if you just adjust to get 0 n wont height be all over the place.my fluid is all new 15 on graduation test it does need to be levelled slightly , but my front n readings are fr 13.4 and fl -17.4.HELP

The frustrations are understood and respected and your Techstream readout is very strange indeed. Maybe the following notes will help you and maybe help others with similar questions:

• All three Height Control Sensors and their linkages, electrical connectors and harnesses must be confirmed to be in reliable condition and capable of performing as intended. If in doubt, removal, dis-assembly, cleaning, electrical testing are essential. Replacement of old Sensors may be the best course of action.

• As you already recognise, ‘cross-leveling’ at the Front must be done properly at the start. All height adjustments of any kind are done with vehicle on a level surface, no driver nor passengers nor any other variable load on board, except fuel which should be full. It is vital to equalise static front hub-to-fender heights, with the vehicle set at “N”height, using a tape-measure (nothing to do with Techstream or other scanners), must be done before anything else, with Torsion Bar adjusters only, with engine and AHC “OFF” per attached FSM extract, within 10 millimetres (0.39 inches) side-to- side difference or better, actual measurements do not matter, just equalise Front Right and Front Left in this step – otherwise all else that follows will be built on a mistake and ongoing frustration is guaranteed,

• With ‘cross-levelling’ correct, move to adjusting ‘operating heights’ (also called ‘ride heights’) of the vehicle. The relevant targets for ‘ride heights’ for a non-lifted vehicle are the well-known IH8MUD recommendations: Front 19.75 inches or 500 millimetres on both sides; Rear 20.50 inches or 520 millimetres on both sides These are reliable approximations of the more detailed height measurements prescribed in the FSM. All measurements are by tape-measure, with the vehicle set at “N”height, nothing to do with Techstream or other scanners – these are not yet required. The Front heights are set correctly (or nearly correct) first. Setting Rear height comes later and ‘fine tuning’ Front and Rear also comes later.

• The easiest way to raise height in a controlled manner is to use the “ACTIVE TEST” per FSM, or, see last page of second attachment (bridging relevant pins at DLC1 is easier than at DLC3). Raise the front to the desired hub-to-fender distance. Maybe raise a little (or lower), measure with tape-measure, raise again until correct tape-measured front hub-to-fender height is reached. When satisfied, stop and switch engine “OFF. The vehicle will stay at this tape-measured height -- unless there is a problem with, say, internal leakage at the Levelling Valves inside the Control Valve Assembly or with the Return Valve at the AHC Pump, or some other unusual problem, or unless the engine is switched “ON” and the AHC is allowed to self-level. So engine and AHC remain ‘’OFF” for now. Techstream or other scanner are not required yet.

• Alternatively, (and many people do it this way), use front Height Control Sensor slide adjusters (easier than heim bolts) to cause the Front to raise (or lower), maybe in a couple of steps, until the required front hub-to-fender tape-measured height is achieved. For safety, move both sliders a little with the engine “OFF”, then restart engine to allow vehicle and AHC to find the new height, drive around the block if necessary, then tape-measure the front hub-to-fender heights again while engine and AHC are still “ON”. Repeat until satisfied that the required tape-measured hub-to-fender 'ride height' has been achieved, then switch the engine “OFF”. As above, the vehicle will stay at this height unless something is very wrong in the system or unless the vehicle is re-started and moved, causing the system to attempt to self-level unhelpfully.

• FOR PERSONAL SAFETY, AVOID ADJUSTING HEIGHT CONTROL SENSORS WITH HEAD OR HANDS OR OTHER BODY PARTS IN THE WHEEL ARCHES OR UNDER THE BODY WHILE THE ENGINE IS “ON” AND THE AHC SYSTEM IS ACTIVE. A MISTAKE OR UNINTENDED MOVEMENT OF THE VEHICLE BODY ONTO THE HUMAN BODY WOULD EASILY CAUSE SERIOUS INJURY.

• @PADDO describes a safe method at this Post #2 in this thread:
  High as a kite, hard as a rock! (Yes AHC again...) - https://forum.ih8mud.com/threads/high-as-a-kite-hard-as-a-rock-yes-ahc-again.1119157/#post-12149330

• When the vehicle is stationary, the Gate Valves in the Control Valve Assembly are open and Front Right and Front Left AHC pressures are equal. The Front Right and Front Left hub-to-fender heights CANNOT be set differently by using the Right and Left front Height Control Sensor slide adjusters or heim adjuster bolts. [Note: The LC100/LX470 AHC system is a two-channel system capable of raising/lowering Front and Rear of the vehicle. It cannot raise/lower each of the four corners independently – this would require a four-channel system]. So no need to try too hard for exactly equal Height Control Sensor movements nor even bother with Techstream at this stage because Sensor differences cannot cause different 'ride heights' on either side. The aim is simply to achieve the required tape-measured Front hub-to-fender 'ride height'. The engine is still "OFF". Techstream or other scanner is not required at this stage.

• Now double-check that ‘cross-level’ is still correct and has not been disturbed. Some variation can occur, mainly due to wear or differences in mechanical components of the suspension. Readjust ‘cross-level’ if necessary, with engine still “OFF”, using only Torsion Bar adjusters.

• The engine and AHC system remains “OFF” until the relevant step later in the sequence below.

• When satisfied that the vehicle has been correctly ‘cross-levelled’ at the Front AND when satisfied that Front ‘ride height’ is now correct, the next aim is to set the Front Height Control Sensors to read zero +/- 5 millimetre or +/- 0.20 inches at this ‘ride height’.

• The AHC system is designed to self-level the vehicle at the ‘ride height corresponding to “N” at height select switch on the centre console. The Front hub-to-fender height has now been established in the foregoing procedure and the vehicle is now sitting at the correct Front hub-to-fender 'ride height' for “N”. If the centre console switch is set to “LO” or to “HI”, then the ECU will choose the heights that correspond to those settings. It is not necessary make further adjustments for “LO” or “HI” height selections. [More detail on the operation of the AHC system and the role of the Height Control Sensors has been written up in a different thread for a different purpose but may assist with understanding – see Ahc problems. - https://forum.ih8mud.com/threads/ahc-problems.1242268/#post-13722174 ]

• Anyway, now is the time to break out Techstream or other scanner and connect to the vehicle with the Ignition Key “ON” but DO NOT start the engine as this would cause the AHC ECU to attempt an unwanted self-levelling effort. Now read both Front Height Control Sensor readings on Techstream or other scanner WITHOUT starting the engine.

• Now move both Front Height Control Sensor slider adjusters WITHOUT starting the engine until the reading is as close as possible to Zero +/- 5 millimetre or +/- 0.20 inches. The heim threaded bolt can be used for fine adjustment but be aware that this is very fiddly.

View attachment 2642680

• When satisfied, tighten all lock-nuts. Start the vehicle engine, test drive around the block until the suspension settles, then re-check all tape-measurements and also the Techstream readout and make such further adjustments as may be necessary. Some iterations and fine tuning should be expected.

• If all has gone well, at this point the vehicle has been front ‘cross levelled’, front ‘ride height’ at “N” have been set, and the Front Height Control Sensors are set correctly to cause the AHC to self-level the Front to the correct Front hub-to-fender height, with Techstream readings close to Zero +/- 5 millimetre or +/- 0.20 inches

• If the vehicle then fails to self-level at the correct tape-measured front hub-to-fender ‘ride heights and near-zero Sensor readings, then there are problems elsewhere. These may be resolved when the Rear settings are correctly adjusted, or ‘cross levelling’ may be incorrect, or there are one or more faulty Height Control Sensors, linkages, connectors or harness.

• Conduct a similar process to achieve correct Rear hub-to-fender ‘ride height’ and to correctly set the single Rear Height Control Sensor. This task is simpler but the Rear Sensor is less accessible. It is mounted on chassis cross-member in front of the rear diff and connects to the Left Rear Upper Control Arm.

• AGAIN FOR PERSONAL SAFETY, AVOID ADJUSTING HEIGHT CONTROL SENSORS WITH HEAD OR HANDS OR OTHER BODY PARTS UNDER THE BODY WHILE THE ENGINE IS “ON” AND THE AHC SYSTEM IS ACTIVE. A MISTAKE OR UNINTENDED MOVEMENT OF THE VEHICLE BODY ONTO THE HUMAN BODY COULD EASILY CAUSE SERIOUS INJURY. USE LOCKED STANDS UNDER THE CHASSIS TO RESTRICT ANY UNPLANNED MOVEMENT AND FOR PERSONAL PROTECTION.

View attachment 2642685

• When Front and Rear Heights are correct, AHC Neutral Pressures can be measured correctly and compared with FSM specifications – wrong heights means misleading AHC Neutral Pressure results.

• When Front and Rear Heights are correct AND AHC Neutral Pressures also are correct, a correct reading of the difference in the levels of the fluid in the AHC Tank between “LO” and “HI” can be taken to indicate overall globe condition – wrong AHC pressures means misleading results in this test.

Some comments on @saudi data in Post #187:

Front Right Height Control Sensor: +13.4 millimetres (from Techstream)
Front Left Height Control Sensor: -17.4 millimetres (from Techstream)
Rear Height Control Sensor: -2.6 millimetres (from Techstream -- there is only one Rear Sensor)

Actual Sensor differences on @saudi vehicle:

Difference, Right Front to Left Front: 30.8 millimetres
Difference, Right Front to Rear: 16.0 millimetres
Difference, Left Front to Rear: 14.8 millimetres

Factory Service Manual (FSM) specification for Height Control Sensor readings at "N":

zero +/- 5 millimetres or +/- 0.20 inches

Ride quality is not reported for @saudi vehicle – essential information for diagnosis and explanation.

Tape measurements at all four wheels of hub-to-fender ‘Ride heights’ at “N” setting are not reported for @saudi vehicle – essential information for diagnosis and explanation.

Additional Techstream information provided for @saudi vehicle:

Front AHC pressure: 6.1 Mpa -- this is a little low
Rear AHC pressure: 2.4 MPa -- this is incredibly low? What are rear hub-to-fender tape measurements?
Accumulator pressure: 10.6 Mpa – normal

FSM specifications for AHC Neutral Pressures at "N" height is found at https://lc100e.github.io/manual/
then tab Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM (IFS) > ON-VEHICLE INSPECTION

Steering angle: -258.75 degrees – very unusual -- with steering straight ahead this should be close to zero, greater than about 36 degrees will affect Gate Valve operation in the Control Valve Assembly and cause ride quality differences in Left and Right turns due to different operation of the Damping Force Control Actuators on either side of the vehicle. See https://lc100e.github.io/manual/
then tab Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > C1781

The huge differences in the @saudi Height Control Sensor readings reported in Techstream are a worry. Such differences are only possible when

• there is one or more faulty Sensors or damage to mechanical linkages, electrical connectors or harness (Special Note: These faults may not generate a DTC code), or,

• new or secondhand Sensors in proven fault-free, good electrical and mechanical condition have been installed and now require adjustment, or,

• cross-levelling is incorrect, or

• there have been previous unsuccessful attempts to adjust existing Height Control Sensors which have resulted in frustration.

Such large differences may also cause the ECU to place the AHC system into one of several ‘fail safe modes’ with consequences for poor ride quality (no variable damping by TEMS) and limited or no AHC height operation.

 

[saudi]

FRont now ok rear a bit strange 20mm higher one side on rear , but you cant adjust ive just had a goverment inspection and all good ,new spring 6 months ago so im a bit pereplexed what to do

 

[IndroCruise]

FRont now ok rear a bit strange 20mm higher one side on rear , but you cant adjust ive just had a goverment inspection and all good ,new spring 6 months ago so im a bit pereplexed what to do

Finding one side at Rear 20 millimetres higher than the other with Front OK certainly is strange.

May I assume you are measuring on a level floor?

If the chassis is straight and true then theoretically it should behave like a large stiff rectangle in one plane, meaning that if one corner is high (such as when one rear coil is stronger than the other), then the diagonally opposite corner should be low. The chassis won’t be perfect ex-factory – but it would have been built in a jig with only a narrow manufacturing tolerance, otherwise the whole geometry of the vehicle and its suspension and steering would be compromised even when new. An older vehicle may have lost some dimensional precision over time, especially if it has had a rough life or been involved in an accident at some point in its history, either of which may have resulted in some chassis twist or some suspension damage.

Or there may be an issue with some part of the mechanical suspension – for example, if there is damage or heavy wear (such as deformation of front control arms or disintegrating bushes or worn-out ball joints or worn bearings etc) somehow on only one side of the front suspension, then the chassis may sit lower than it should relative to the wheel hub at that corner. Equalising the front hub-to-fender heights (cross-levelling) will not correct the underlying mechanical condition and instead the diagonally opposite rear corner would then be expected to sit higher than it should.

Also be wary of different overall tyre diameters such as may occur as a result of mixing different types/sizes of tyres, or mixing tyres with very different amounts of wear. Tyre differences also may cause a vehicle to sit unevenly.

For these kinds of issues, it may be necessary to revert to the actual FSM method of determining vehicle height rather than the commonly used IH8MUD approximations discussed previously. These measurements are fiddly but checking the measurements on the vehicle and comparing them may reveal the cause of variance -- see picture below and
https://lc100e.github.io/manual/ then tabs
Repair Manual > SUSPENSION AND AXLE > FRONT WHEEL ALIGNMENT (IFS) > INSPECTION

In any case, a hub-to-fender variance of 20 millimetres (more than three-quarters of an inch) seems like a lot of difference.

Would you mind please posting the actual hub-to-fender measurements at all four wheel positions?

Rather than speculate further from a great distance, may I also suggest getting a good suspension or wheel alignment workshop to inspect the vehicle? If they are well-experienced, they should be able to identify very quickly why this variance has arisen.

Other IH8MUD Members may be able to offer better ideas.

In addition, I have tagged @Moridinbg because recently has completely dismantled and re-assembled his LC100 with AHC and he may be willing to offer an opinion about the kinds of dimensional effects you are seeing. If you have not seen his amazing, very well illustrated thread, it is definitely worth viewing:
HDJ100 - Body off renovation, now with a hot dip galvanised frame *Picture Heavy* | IH8MUD Forum

 

[saudi]

Finding one side at Rear 20 millimetres higher than the other with Front OK certainly is strange.

May I assume you are measuring on a level floor?

If the chassis is straight and true then theoretically it should behave like a large stiff rectangle in one plane, meaning that if one corner is high (such as when one rear coil is stronger than the other), then the diagonally opposite corner should be low. The chassis won’t be perfect ex-factory – but it would have been built in a jig with only a narrow manufacturing tolerance, otherwise the whole geometry of the vehicle and its suspension and steering would be compromised even when new. An older vehicle may have lost some dimensional precision over time, especially if it has had a rough life or been involved in an accident at some point in its history, either of which may have resulted in some chassis twist or some suspension damage.

Or there may be an issue with some part of the mechanical suspension – for example, if there is damage or heavy wear (such as deformation of front control arms or disintegrating bushes or worn-out ball joints or worn bearings etc) somehow on only one side of the front suspension, then the chassis may sit lower than it should relative to the wheel hub at that corner. Equalising the front hub-to-fender heights (cross-levelling) will not correct the underlying mechanical condition and instead the diagonally opposite rear corner would then be expected to sit higher than it should.

Also be wary of different overall tyre diameters such as may occur as a result of mixing different types/sizes of tyres, or mixing tyres with very different amounts of wear. Tyre differences also may cause a vehicle to sit unevenly.

For these kinds of issues, it may be necessary to revert to the actual FSM method of determining vehicle height rather than the commonly used IH8MUD approximations discussed previously. These measurements are fiddly but they may reveal the cause of variance -- see picture below and
https://lc100e.github.io/manual/ then tabs
Repair Manual > SUSPENSION AND AXLE > FRONT WHEEL ALIGNMENT (IFS) > INSPECTION

View attachment 2643045

In any case, a hub-to-fender variance of 20 millimetres (more than three-quarters of an inch) seems like a lot of difference.

Would you mind please posting the actual hub-to-fender measurements at all four wheel positions?

Rather than speculate further from a great distance, may I also suggest getting a good suspension or wheel alignment workshop to inspect the vehicle? If they are well-experienced, they should be able to identify very quickly why this variance has arisen.

Other IH8MUD Members may be able to offer better ideas.

In addition, I have tagged @Moridinbg because recently has completely dismantled and re-assembled his LC100 with AHC and he may be willing to offer an opinion about the kinds of dimensional effects you are seeing. If you have not seen his amazing, very well illustrated thread, it is definitely worth viewing:
HDJ100 - Body off renovation, now with a hot dip galvanised frame *Picture Heavy* | IH8MUD Forum

Ok tomorrow I’m going to level car with a spirit level that way I can check more accurately. Finding level ground is difficult as uk roads have camber. Will let u know. I have a feeling the ground I’m checking on may not be as level as it seems so a slight lean could cause this

 

[saudi]

Finding one side at Rear 20 millimetres higher than the other with Front OK certainly is strange.

May I assume you are measuring on a level floor?

If the chassis is straight and true then theoretically it should behave like a large stiff rectangle in one plane, meaning that if one corner is high (such as when one rear coil is stronger than the other), then the diagonally opposite corner should be low. The chassis won’t be perfect ex-factory – but it would have been built in a jig with only a narrow manufacturing tolerance, otherwise the whole geometry of the vehicle and its suspension and steering would be compromised even when new. An older vehicle may have lost some dimensional precision over time, especially if it has had a rough life or been involved in an accident at some point in its history, either of which may have resulted in some chassis twist or some suspension damage.

Or there may be an issue with some part of the mechanical suspension – for example, if there is damage or heavy wear (such as deformation of front control arms or disintegrating bushes or worn-out ball joints or worn bearings etc) somehow on only one side of the front suspension, then the chassis may sit lower than it should relative to the wheel hub at that corner. Equalising the front hub-to-fender heights (cross-levelling) will not correct the underlying mechanical condition and instead the diagonally opposite rear corner would then be expected to sit higher than it should.

Also be wary of different overall tyre diameters such as may occur as a result of mixing different types/sizes of tyres, or mixing tyres with very different amounts of wear. Tyre differences also may cause a vehicle to sit unevenly.

For these kinds of issues, it may be necessary to revert to the actual FSM method of determining vehicle height rather than the commonly used IH8MUD approximations discussed previously. These measurements are fiddly but checking the measurements on the vehicle and comparing them may reveal the cause of variance -- see picture below and
https://lc100e.github.io/manual/ then tabs
Repair Manual > SUSPENSION AND AXLE > FRONT WHEEL ALIGNMENT (IFS) > INSPECTION

View attachment 2643045

In any case, a hub-to-fender variance of 20 millimetres (more than three-quarters of an inch) seems like a lot of difference.

Would you mind please posting the actual hub-to-fender measurements at all four wheel positions?

Rather than speculate further from a great distance, may I also suggest getting a good suspension or wheel alignment workshop to inspect the vehicle? If they are well-experienced, they should be able to identify very quickly why this variance has arisen.

Other IH8MUD Members may be able to offer better ideas.

In addition, I have tagged @Moridinbg because recently has completely dismantled and re-assembled his LC100 with AHC and he may be willing to offer an opinion about the kinds of dimensional effects you are seeing. If you have not seen his amazing, very well illustrated thread, it is definitely worth viewing:
HDJ100 - Body off renovation, now with a hot dip galvanised frame *Picture Heavy* | IH8MUD Forum

I see your in Australia I used to live in Albany Western Australia

 

[menancyandsam]

Why does the FSM state a full load w/ full tank but no occupants? There will always be a driver so why leave him/her out in calculating AHC pressures.
With me in car 220lbs I get 6.4/6.2 (Front/Rear).
With me out of the car, I get 5.8/5.7

With me in I'm at spec (a touch low on the front) but if I go by FSM I need to adj. to higher pressures.

 

[IndroCruise]

Why does the FSM state a full load w/ full tank but no occupants? There will always be a driver so why leave him/her out in calculating AHC pressures.
With me in car 220lbs I get 6.4/6.2 (Front/Rear).
With me out of the car, I get 5.8/5.7

With me in I'm at spec (a touch low on the front) but if I go by FSM I need to adj. to higher pressures.

All is good -- nothing to worry about here. It would be very remiss of Toyota/Lexus (or any manufacturer) and also poor engineering to provide specifications such as AHC pressure specifications and test methods without a reference point or defined standard conditions which

• are easy to understand and replicate, and,
• enable easy comparisons, and,
• from which other allowances and adjustments can be made for different load conditions and/or "lifted" height conditions, and,
• without assumptions about, or somehow averaging, the widely different weight of individuals or other loadings (because AHC pressures change with load), and very importantly,
• at a specified standard height as shown in pic at Post #194 in this thread (because AHC pressures change with height) -- for example, pressures will be too high at "N" height in a "lifted" vehicle unless compensated by torsion bar adjustment and spring selection, etc.

None of this restricts the Owner in any way. It simply provides the Owner with basic information so that he/she can make any allowances or adjustments necessary for his/her different circumstances, especially load in or on the vehicle, and, height of the vehicle.

The point of it all is to help Owners understand that AHC pressures must be brought back into the specified range -- and preferably at the lower end -- if best TEMS adaptive variable damping performance (which gives best ride comfort), and, best AHC self-levelling and raise/lower performance, are all to be achieved. In detail, this means that the nitrogen behind the membranes in healthy 'globes' is not so compressed by AHC fluid overpressure that fluid movement through the Damping Force Control Actuators is not so reduced as to inhibit damping, and, "raise" requirements are not beyond the capability of the Height Control Accumulator and the AHC Pump.

Seems like your AHC pressures are very well chosen -- add passengers and their stuff or other loads and accessories (within limits) and your AHC pressures most likely still will be within the specified ranges for good ride comfort. Well done!

It gets worse -- the FSM suggests that an "average person" is 68 kilograms or 150 pounds. I vaguely remember when I was that weight -- I think I was still at school!!

Source: https://lc100e.github.io/manual/, then tabs New Car Features > CHASSIS > Suspension > Active Height Control Suspension & Skyhook TEMS

 

[menancyandsam]

That make sense, thank you.
So measure with me out of the car is best, but 5.8 front seems too low what do you think. I believe spec is 6.9 +- .5

 

[saudi]

Ok tomorrow I’m going to level car with a spirit level that way I can check more accurately. Finding level ground is difficult as uk roads have camber. Will let u know. I have a feeling the ground I’m checking on may not be as level as it seems so a slight lean could cause this

Ok got it as best as I can now level front and rear , I’ve also go height ok however couldn’t do n as the rods too rusted so ordered new ones , here is the readings