The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (6 Viewers)

[Oldsman71442]

Any ideas why my drivers side torsion bar is extremely hard to turn and the passenger side is easy. It’s not cross threaded or corroded. I have completely removed the assembly and reinstalled it. It’s proving to be a pain in the butt getting my pressure in spec

 

[IndroCruise]

Any ideas why my drivers side torsion bar is extremely hard to turn and the passenger side is easy. It’s not cross threaded or corroded. I have completely removed the assembly and reinstalled it. It’s proving to be a pain in the butt getting my pressure in spec

Sometimes there can be minor corrosion at the thread within the adjuster, not visible but enough to resist turning. Several soakings over several days with your favourite penetrating oil may help. Also try raising to "HI" to reduce load on torsion bar, or even jack vehicle until wheel is off the ground, to help get started (place safety stands under vehicle) -- just make sure that all actual height and pressure measurements are made with wheels on ground at "N" height.

 

[Oldsman71442]

Sometimes there can be minor corrosion at the thread within the adjuster, not visible but enough to resist turning. Several soakings over several days with your favourite penetrating oil may help. Also try raising to "HI" to reduce load on torsion bar, or even jack vehicle until wheel is off the ground, to help get started (place safety stands under vehicle) -- just make sure that all actual height and pressure measurements are made with wheels on ground at "N" height.

Thanks. I am measuring it in normal height and even in high/system off and wheel off ground it’s super difficult. I think I finally got my pressures in spec but seriously took everything I had to turn the drivers and my 2 year old could have done the passenger one lol

 

[ramangain]

Thanks. I am measuring it in normal height and even in high/system off and wheel off ground it’s super difficult. I think I finally got my pressures in spec but seriously took everything I had to turn the drivers and my 2 year old could have done the passenger one lol

This is normal BTW on every AHC equipped Hundy I've come across. I've always had to use a 2''+ long cheater pipe on the drivers side.

 

[Jaz]

Thanks for all the hard work putting together this thread, I am against removing AHC and specifically bought a car with this feature.
The information here will hopefully let me keep it working and I will certainly be giving it a good check over when I have room in the garage.

 

[auchief]

Hello, looking for some feedback on these numbers.

I went from these:

To these have 6 full cranks on the Tabs:

Height measurements:
PS Front 19.25 in
DS Front 19.5 in

PS Rear 20.75 in
DS Rear 20 in

I'm thinking I need new springs in the rear to get that pressure right.

Also, noticed that my AHC reservoir is overfull maybe? I had the Lexus dealership flush and replace my fluid a couple of years ago when I bought the truck and just now noticed this in N.

 

[drspace5]

Anyone know any specialists in or near Denver that can perform a full test/servicing of AHC system?

 

[Muhammad Rais]

Here is a little run down of what led me in to this situation. Due to the condition of the existing parts I replaced UCA/ LCA, CV axle boots from Toyota, front diff seals on the both sides, outer tie rod end, front brakes and rotor, including re grease wheel bearings, new bushings for all 5 rear control arms. I used super pro bushings and 555 ball joints from cruiser outfitters. During all this work I had take torsion bars off for lower control arm bushings chassis. I didn’t mark anything on torsion bars and put it back. I don’t even remember about the front height sensors. I installed them back but not sure what adjustment it was before. As far the rear sensor that was installed wrong initially. We installed rear upper control arms in a wrong way so the bracket was in the opposite direction. Didn’t realize that till I 1st test drive and there was OFF blinking at the dash. So I looked at it and found rear sensor was squeezed because of wrong arm installation. Before I fixed it the height was higher than I correctly install the arm and sensor. Once I re installed them it sits way low and doesn’t move at all on L or N. Front of the vehicle still moving on L N H but nothing happening on the rear. System was totally working fine before all this work took place. I was able to connect tech stream and found 1 fault code and took AHC data screenshot.
I ordered a used oem rear sensor and also new aftermarket one just to see which one works. Didn’t get a chance to install them yet. Before I saw this thread looking at YotaMD video on YouTube I contacted him and described everything. My next plan is to install the new rear height sensor and go from there. I am concerned about 3 major points.
1. Both of the front sensors installed but not in the past position on the sliders because I don’t have any before pictures.
2. Rear height sensors sliding position
3. I didn’t mark up anything on torsion bars so have no clue what will be the right way to install.
I was looking for a reindex torsion bar thread but didn’t find anything helpful.
once I install the rear sensor I will let you all know. Here are the screenshots with faulty sensor.

I found this thread yesterday and keep reading every pages. I really hope I can fix my AHC otherwise have no clue how to proceed. I reached out to few local guys for help but nothing yet.
this thread is an awesome source for AHC. Thank you all for put it together. It’s full of knowledge about AHC.

 

[IndroCruise]

Hello, looking for some feedback on these numbers.

I went from these:
View attachment 2673471

To these have 6 full cranks on the Tabs:

View attachment 2673468

Height measurements:
PS Front 19.25 in
DS Front 19.5 in

PS Rear 20.75 in
DS Rear 20 in

I'm thinking I need new springs in the rear to get that pressure right.

Also, noticed that my AHC reservoir is overfull maybe? I had the Lexus dealership flush and replace my fluid a couple of years ago when I bought the truck and just now noticed this in N.

View attachment 2673470

Basically, these are good numbers!

Starting point: Front cross-level is good -- only 0.25 inches difference Left to Right -- which is within FSM tolerance of 0.39 inches (10 millimetres) -- see attached. Maybe you could tweak the Torsion Bar adjusters just a little, if you wanted to pursue perfection at the recommended 19.75 inches equal hub-to-fender at the front. Theoretically, if Left Front (DS) was a little low, then you could expect the diagonally opposite Right Rear (PS) to be a little high, which does not show here, but it only takes small differences -- side-to-side tyre types, or tyre wear, or tyre pressures, or wheel alignment, or wear in suspension parts and bushes, or not quite level ground where measurements were taken, or vehicle load or fittings not quite distributed evenly, or imperfections in this 18 year old chassis -- to make small but measurable differences in how a vehicle sits. The 'tolerance' mentioned in the FSM acknowledges these kinds of effects.

Next, consider 'ride heights' all round. The tape measurements are best taken at "N" height in FSM weight condition (no load, no driver, no pax, full fuel) with engine and AHC still running on a level surface after a trip around the block to make sure that the suspension is settled and that the AHC system has finished doing any auto-levelling. The measurements look reasonable -- comments as above. Height adjustment is done with the Height Control Sensor adjusters (not the torsion bar adjusters except for cross-levelling at the front) but does not appear to be worth the trouble based on the final measurements given above.

Then consider Height Sensor readings on Techstream. The final measurements above just scrape into the FSM tolerance of +/- 5 millimetres (+/- 0.2 inches). Tweaking cross-level as above would have some effect and may bring these readings closer together without any further effort. With heights correct at "N", as measured hub-to-fender by tape measure (looking for Front 19.75 inches and Rear 20.50 inches), you could consider adjusting the Height Control Sensors to zero -- involves Techstream connected and watched, ignition key "ON" but engine "OFF" (don't want AHC doing any auto-levelling during adjustments), move slider adjusters (or heim bolts) to achieve as close as possible to zero on the Techstream read-out. This is chasing perfection and does not seem worthwhile in your case.

Then with vehicle 'ride heights' correct as measured hub-to-fender by tape measure, operate AHC: "N" to "LO" (allow to settle), then "LO" to "HI" (allow to settle, ensure pump has stopped after re-charging Height Control Accumulator), then record AHC pressure readings -- repeat measurements say three times to be sure of reliable readings.

Front AHC pressure is good. Rear AHC pressure does suggest new OEM rear springs to reduce AHC pressure (add spacers to give a little more pressure reduction), or, upgrade to King KTRS-79 springs if consistent heavy loads or fittings are in your future.

Finally, with AHC pressures correct, it is good to check overall 'globe' condition by observing the AHC Tank level at "LO" and at "HI". A difference of 14 graduations indicates that 'globes' are as new; 7 graduations indicates that it is time to replace 'globes'. 'Globes' are 'wear items' and eventually require replacement.

The depicted excessive AHC Fluid level is harmless unless the vehicle is travelling over very steep gradients when spillage from an overfull tank is a possibility. If the last AHC Fluid change was "a couple of years ago", it would be good to change the fluid again so as to better maintain the overall AHC system. This is an easy DIY task, well explained in several good IH8MUD threads.

 

[auchief]

Basically, these are good numbers!

Starting point: Front cross-level is good -- only 0.25 inches difference Left to Right -- which is within FSM tolerance of 0.39 inches (10 millimetres) -- see attached. Maybe you could tweak the Torsion Bar adjusters just a little, if you wanted pursue perfection at the recommended 19.75 inches equal hub-to-fender at the front. Theoretically, if Left Front (DS) was a little low, then you could expect the diagonally opposite Right Rear (PS) to be a little high, which does not show here, but it only takes small differences -- side-to-side tyre types, or tyre wear, or tyre pressures, or wheel alignment, or wear in suspension parts and bushes, or not quite level ground where measurements were taken, or vehicle load or fittings not quite distributed evenly, or imperfections in this 18 year old chassis -- to make small but measurable differences in how a vehicle sits. The 'tolerance' mentioned in the FSM acknowledges these kinds of effects.

Next, consider 'ride heights' all round. The tape measurements are best taken at "N" height in FSM weight condition (no load, no driver, no pax, full fuel) with engine and AHC still running on a level surface after a trip around the block to make sure that the suspension is settled and that the AHC system has finished doing any auto-levelling. The measurements look reasonable -- comments as above. Height adjustment is done with the Height Control Sensor adjusters (not the torsion bar adjusters except for cross-levelling at the front) but does not appear to be worth the trouble based on the final measurements given above.

Then consider Height Sensor readings on Techstream. The final measurements above just scrape into the FSM tolerance of +/- 5 millimetres (+/- 0.2 inches). Tweaking cross-level as above would have some effect and may bring these readings closer together without any further effort. With heights correct at "N", as measured hub-to-fender by tape measure (looking for Front 19.75 inches and Rear 20.50 inches), you could consider adjusting the Height Control Sensors to zero -- involves Techstream connected and watched, ignition key "ON" but engine "OFF" (don't want AHC doing any auto-levelling during adjustments), move slider adjusters (or heim bolts) to achieve as close as possible to zero. This is chasing perfection and does not seem worthwhile in your case.

Then with vehicle 'ride heights' correct as measured hub-to-fender by tape measure, operate AHC: "N" to "LO" (allow to settle), then "LO" to "HI" (allow to settle, ensure pump has stopped after re-charging Height Control Accumulator), then record AHC pressure readings -- repeat measurements say three times to be sure of reliable readings.

Front AHC pressure is good. Rear AHC pressure does suggest new OEM rear springs to reduce AHC pressure (add spacers to give a little more pressure reduction), or, upgrade to King KTRS-79 springs if consistent heavy loads or fittings are in your future.

Finally, with AHC pressures correct, it is good to check overall 'globe' condition by observing the AHC Tank level at "LO" and at "HI". A difference of 14 graduations indicates that 'globes' are as new; 7 graduations indicates that it is time to replace 'globes'. 'Globes' are 'wear items' and eventually require replacement.

The depicted excessive AHC Fluid level is harmless unless the vehicle is travelling over very steep gradients when spillage from an overfull tank is a possibility. If the last AHC Fluid change was "a couple of years ago", it would be good to change the fluid again so as better maintain the overall AHC system. This is an easy DIY task, well explained in several good IH8MUD threads.

Excellent and thorough reply, confirming basically what I thought. I can chase perfect height numbers, but I feel like maybe I should leave it alone. I figured based on the numbers I need some new springs. I don't have a lot of heavy towing in my future so I'm thinking new OEM (probably the Toyota part numbers from the AHC equipped later model 100 LCs). Thanks again, and I will update if/when I start chasing those height numbers and/or get new springs.

 

[IndroCruise]

Here is a little run down of what led me in to this situation. Due to the condition of the existing parts I replaced UCA/ LCA, CV axle boots from Toyota, front diff seals on the both sides, outer tie rod end, front brakes and rotor, including re grease wheel bearings, new bushings for all 5 rear control arms. I used super pro bushings and 555 ball joints from cruiser outfitters. During all this work I had take torsion bars off for lower control arm bushings chassis. I didn’t mark anything on torsion bars and put it back. I don’t even remember about the front height sensors. I installed them back but not sure what adjustment it was before. As far the rear sensor that was installed wrong initially. We installed rear upper control arms in a wrong way so the bracket was in the opposite direction. Didn’t realize that till I 1st test drive and there was OFF blinking at the dash. So I looked at it and found rear sensor was squeezed because of wrong arm installation. Before I fixed it the height was higher than I correctly install the arm and sensor. Once I re installed them it sits way low and doesn’t move at all on L or N. Front of the vehicle still moving on L N H but nothing happening on the rear. System was totally working fine before all this work took place. I was able to connect tech stream and found 1 fault code and took AHC data screenshot.
I ordered a used oem rear sensor and also new aftermarket one just to see which one works. Didn’t get a chance to install them yet. Before I saw this thread looking at YotaMD video on YouTube I contacted him and described everything. My next plan is to install the new rear height sensor and go from there. I am concerned about 3 major points.
1. Both of the front sensors installed but not in the past position on the sliders because I don’t have any before pictures.
2. Rear height sensors sliding position
3. I didn’t mark up anything on torsion bars so have no clue what will be the right way to install.
I was looking for a reindex torsion bar thread but didn’t find anything helpful.
once I install the rear sensor I will let you all know. Here are the screenshots with faulty sensor.
View attachment 2681494
View attachment 2681495
I found this thread yesterday and keep reading every pages. I really hope I can fix my AHC otherwise have no clue how to proceed. I reached out to few local guys for help but nothing yet.
this thread is an awesome source for AHC. Thank you all for put it together. It’s full of knowledge about AHC.

Seems like you have done a LOT of good work and already learned a lot of things. You are in good hands with @suprarx7nut – good idea to refresh understandings on AHC matters from his video and “Cheat Sheet”,

… and also review Post #1 and following posts in this thread started by @LndXrsr.

Let’s start with the torsion bars ….

Yes – it would have been better to have marked everything before disassembly so that it could go back together with more confidence – but you already know all about that.

I have attached a ten year old article about Torsion Bars written by IH8MUD Member @Gunney way back in 2011. It contains some good pictures which maybe helpful. The article is about Non-AHC Landcruisers. Be very careful not to become confused. Ignore all the dimensions and measurements. AHC Torsion Bars and how they work with the AHC system are different. However, I thought that some of the pictures could assist.

In the case of your Torsion Bars and how they work on your AHC vehicle, consider the following:

If both torsion bars are “under-indexed” and equal, then there will not be enough spring effect, not enough weight carried by torsion bars, too much weight carried by AHC system, Front AHC pressure will be too high, giving poor damping and a harsh, bumpy ride quality -- and there may not be enough adjustment thread at the torsion bar adjusters to achieve correct AHC pressures.

If both torsion bars are “over-indexed” and equal, then there will be too much spring effect, too much weight carried by torsion bars, too little weight carried by AHC system, Front AHC pressure will be too low, also giving poor damping but with a ‘springy’ ride quality -- and there may not be enough adjustment thread at the torsion bar adjusters to achieve correct AHC pressures.

If the two torsion bars are indexed very differently, there will be an obvious ‘lean’ across the front of the vehicle when they are equally loaded. Inspect this on level ground with no driver, no load, no pax in vehicle, fuel tanks full, and with engine and AHC “OFF”. In this condition, the Gate Valves in the AHC Control Valve Assembly are open, Left and Right sides of the vehicle are connected hydraulically and are at equal pressures. If there is a ‘lean’ across the front, then it is due to unequal deflections by each torsion bar. If one front corner is low, the diagonally opposite rear corner usually will be high (unless there are some other effects – see Post #209 in this thread).

All is not lost. The situation is recoverable.

First, carry out the ‘cross levelling’ procedure per FSM – see attachment. It is assumed that the torsion bars are in good condition and have the same ‘spring rate’. The purpose of ‘cross levelling’ is to ensure that both torsion bars are carrying equal shares of the vehicle front weight at the same deflection (movement) of the torsion bar. In a vehicle equipped with AHC, ‘cross levelling’ is NOT about final height adjustment. At this stage, it does not matter what the actual hub-to-fender measurements may be provided that they are equal.

If ‘cross levelling’ cannot be achieved because insufficient thread is available on the torsion bar adjusters due to one or other of the above consequences of incorrect fitment of the torsion bars, then removal and re-indexing of the torsion bars will be required.

Then ‘cross levelling’ must be repeated until equal front hub-to-fender heights are achieved, before proceeding further.

Next, proceed to the Height Control Sensors, and, setting the vehicle hub-to-fender heights at “N” height setting ….

Both of the following references are essential reading for much that follows in these notes:

https://lc100e.github.io/manual/ (genuine Toyota LC100 Factory Service Manual including AHC – also relevant to LX470)
Then follow the index tabs, starting at the top left of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control & Skyhook TEMS

This opens to a 20 page general description and diagrams of the Active Height Control (AHC) system and the Toyota Electronic Modulated Suspension (TEMS) system and how these systems operate.

https://lc100e.github.io/manual/, then follow these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > C1711/11 to C1713/13
which opens at Page DI-224 – suggest print all five pages of this article.

The section and diagrams at Page DI-227 headed “2. Check Height Control Sensor” are especially important.

A simple 4.5 volt test arrangement is described in this FSM extract and can be made up from parts acquired from an electronics or automotive shop. A multimeter suitable for automotive work also will be required.

Suggest proceed as follows:

First, check the condition of each of the Height Control Sensors. This means removing the existing Sensors from the vehicle, then inspecting the linkages for freedom of movement and absence of damage or corrosion, then removing the cover plate and gently cleaning the internals. Then electrically test the Sensor per the second FSM extract referenced above, and also test continuity of the connector and harness and also test the voltage supply from the harness to the Sensor.

Visual inspection alone is insufficient as faults may not be visible to the naked eye. The Sensors work in a low voltage range of about 0.45 volts to about 4.05 volts. The voltage signals the Sensors send to the ECU are easily affected by hard-to-see imperfections in the Sensors as well as wear and tear, moisture, corrosion, poor continuity at connectors and harnesses and/or low incoming voltage.

Conflicting, widely different signals from the three Sensors will cause the ECU to adopt ‘fail safe mode’ as described in the FSM extract, with or without DTC’s. Usually, this will show as widely different Height Control Sensor readings on Techstream or other scanner. In ‘fail safe mode’, AHC operation and TEMS active damping are stopped and poor ride quality is experienced in 'fail safe mode'.

Electrical testing is a ‘must do’ whenever Sensors come off a vehicle AND before installing new Sensors on a vehicle.

Much depends on the correct operation of these Sensors including their connectors and harnesses. It is imperative that they all are reliable. Otherwise, frustration, re-work and wasted time is guaranteed. Height Control Sensor problems are among the most common causes of AHC problems. Depending on the nature of the fault – such as when the Sensor is working but sending an incorrect signal – the Sensor may not throw a Diagnostic Trouble Code (DTC). If in doubt, replace the Sensor.

With ‘cross levelling’ satisfactorily completed AND after fitting tested and reliable Height Control Sensors, it is time to

• adjust the hub-to-fender ‘ride height’ of the vehicle at “N” height, aiming at Front 19.75 inches (500 millimetres), and Rear 20.50 inches (520 millimetres), and also,

• adjust the Height Control Sensors to the correct position (sometimes called the “null position”) in which the Techstream Height Sensor readings are all zero +/- 0.2 inches (or zero +/- 5 millimetres) at “N” height, as specified by FSM. [This corresponds to a signal of about 2.25 volts from the Sensors to the ECU at the “N” height position, as seen in the second FSM extract referenced above. This is the height to which the AHC system is expected to return when “N” is selected at the switch on the centre console, or, when the vehicle is auto-levelling at “N” while in motion. The ECU does this in the background by causing the Levelling Valves and AHC Pump to operate as necessary until the matching ~2.25 volt signal from the Height Control Sensors is found and the required height is achieved with the height switch in “N” position. From this, it can be imagined why the Height Control Sensors and their connectors and harnesses MUST be in good condition for reliable signals and good suspension performance!!]

How to do these two things?

Start the engine, select “N” height at the centre console switch and allow the vehicle to settle.

The Active Test (see last page of the second attachment) can be used to raise the vehicle to the desired height. This involves connecting the pins TS to E1 at DLC1 – this is the receptacle marked DIAGNOSTIC in the engine bay, usually above the Right hand wheel arch. The connector can be an unbent paper clip or similar, nothing special is required. Lights on the dashboard will blink and Techstream will record various faults -- because this connection has the effect of bypassing the controls of the AHC system. This situation will self-correct when the connector is removed later.

When the vehicle is at the required height, turn “OFF” the engine. The Levelling Valves in the Control Valve Assembly will hold the vehicle at this height (assuming all components are healthy) -- unless the engine is turned “ON” again.

Then remove the connector from TS to E1 at DLC1, then turn Ignition Key to “ON” but DO NOT start engine (do not want AHC to attempt auto-levelling during adjustments). If the dashboard AHC light still shows “OFF”, push down on the AHC ON/OFF switch on the centre console to turn “ON” again, select “N” height at the console switch, position the laptop screen so it can be seen using a USB extension cord if that helps, (or use an ELM327 scanner and Bluetooth to a tablet with an app), all doors closed, windows open if desired. (The height selection light in the instrument panel may blink but should show solid green when the adjustments in the next paragraphs are completed).

Then with Ignition Key still "ON", Techstream still "ON", engine still "OFF", and with an eye on the Techstream screen (or other scanner screen) move the sliders on all three proven-healthy Height Control Sensors (two Front, one Rear), one by one, until all Sensor readings are as near as possible to zero, and tighten the locknut. The heim bolts also can be used (front only) but these are very fiddly.

Then pause, check all work so far, drive around the block, re-measure all work, make readjustments as necessary.

With the vehicle now at correct heights front and rear (and only when the vehicle is at correct heights as measured hub-to-fender by tape measure), operate AHC: "N" to "LO" (allow to settle), then "LO" to "N" (allow to settle, ensure pump has stopped after re-charging Height Control Accumulator). Then record AHC pressure readings Front, Rear and Accumulator -- repeat measurements say three times to be sure of reliable readings.

Then turn both of the Torsion Bar adjusters in the same direction until the Front AHC pressure in the correct FSM range is achieved, usually involves about 0.2 Mpa per full turn. The Rear AHC pressure can only be ‘adjusted’ with new OEM springs and spacers or with upgraded springs such as King KTRS-79 if consistent heavy loads or heavy fittings must be considered. The Height Control Accumulator pressure is not adjustable and should be about 10.5 MPa in the pressure test.

Finally, two more points ….

With AHC pressures correct, it is good to check overall 'globe' condition by observing the AHC Tank level at "LO" and at "HI". A difference of 14 graduations indicates that 'globes' are as new; 7 graduations indicates that it is time to replace 'globes'. 'Globes' are 'wear items' and eventually require replacement.

It is good to change the fluid regularly, say every two or three years, so as to better maintain the overall AHC system. This is an easy DIY task, well explained back at Post #1 in this thread and in the video by @suprarx7nut and in several other good IH8MUD threads.

 

[Muhammad Rais]

Seems like you have done a LOT of good work and already learned a lot of things. You are in good hands with @suprarx7nut – good idea to refresh understandings on AHC matters from his video and “Cheat Sheet”,

… and also review Post #1 and following posts in this thread started by @LndXrsr.

Let’s start with the torsion bars ….

Yes – it would have been better to have marked everything before disassembly so that it could go back together with more confidence – but you already know all about that.

I have attached a ten year old article about Torsion Bars written by IH8MUD Member @Gunney way back in 2011. It contains some good pictures which maybe helpful. The article is about Non-AHC Landcruisers. Be very careful not to become confused. Ignore all the dimensions and measurements. AHC Torsion Bars and how they work with the AHC system are different. However, I thought that some of the pictures could assist.

In the case of your Torsion Bars and how they work on your AHC vehicle, consider the following:

If both torsion bars are “under-indexed” and equal, then there will not be enough spring effect, not enough weight carried by torsion bars, too much weight carried by AHC system, Front AHC pressure will be too high, giving poor damping and a harsh, bumpy ride quality -- and there may not be enough adjustment thread at the torsion bar adjusters to achieve correct AHC pressures.

If both torsion bars are “over-indexed” and equal, then there will be too much spring effect, too much weight carried by torsion bars, too little weight carried by AHC system, Front AHC pressure will be too low, also giving poor damping but with a ‘springy’ ride quality -- and there may not be enough adjustment thread at the torsion bar adjusters to achieve correct AHC pressures.

If the two torsion bars are indexed very differently, there will be an obvious ‘lean’ across the front of the vehicle when they are equally loaded. Inspect this on level ground with no driver, no load, no pax in vehicle, fuel tanks full, and with engine and AHC “OFF”. In this condition, the Gate Valves in the AHC Control Valve Assembly are open, Left and Right sides of the vehicle are connected hydraulically and are at equal pressures. If there is a ‘lean’ across the front, then it is due to unequal deflections by each torsion bar. If one front corner is low, the diagonally opposite rear corner usually will be high (unless there are some other effects – see Post #209 in this thread).

All is not lost. The situation is recoverable.

First, carry out the ‘cross levelling’ procedure per FSM – see attachment. It is assumed that the torsion bars are in good condition and have the same ‘spring rate’. The purpose of ‘cross levelling’ is to ensure that both torsion bars are carrying equal shares of the vehicle front weight at the same deflection (movement) of the torsion bar. In a vehicle equipped with AHC, ‘cross levelling’ is NOT about final height adjustment. At this stage, it does not matter what the actual hub-to-fender measurements may be provided that they are equal.

If ‘cross levelling’ cannot be achieved because insufficient thread is available on the torsion bar adjusters due to one or other of the above consequences of incorrect fitment of the torsion bars, then removal and re-indexing of the torsion bars will be required.

Then ‘cross levelling’ must be repeated until equal front hub-to-fender heights are achieved, before proceeding further.

Next, proceed to the Height Control Sensors, and, setting the vehicle hub-to-fender heights at “N” height setting ….

Both of the following references are essential reading for much that follows in these notes:

https://lc100e.github.io/manual/ (genuine Toyota LC100 Factory Service Manual including AHC – also relevant to LX470)
Then follow the index tabs, starting at the top left of the opening page:
New Car Features > CHASSIS > Suspension > Active Height Control & Skyhook TEMS

This opens to a 20 page general description and diagrams of the Active Height Control (AHC) system and the Toyota Electronic Modulated Suspension (TEMS) system and how these systems operate.

https://lc100e.github.io/manual/, then follow these tabs:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > C1711/11 to C1713/13
which opens at Page DI-224 – suggest print all five pages of this article.

The section and diagrams at Page DI-227 headed “2. Check Height Control Sensor” are especially important.

A simple 4.5 volt test arrangement is described in this FSM extract and can be made up from parts acquired from an electronics or automotive shop. A multimeter suitable for automotive work also will be required.

Suggest proceed as follows:

First, check the condition of each of the Height Control Sensors. This means removing the existing Sensors from the vehicle, then inspecting the linkages for freedom of movement and absence of damage or corrosion, then removing the cover plate and gently cleaning the internals. Then electrically test the Sensor per the second FSM extract referenced above, and also test continuity of the connector and harness and also test the voltage supply from the harness to the Sensor.

Visual inspection alone is insufficient as faults may not be visible to the naked eye. The Sensors work in a low voltage range of about 0.45 volts to about 4.05 volts. The voltage signals the Sensors send to the ECU are easily affected by hard-to-see imperfections in the Sensors as well as wear and tear, moisture, corrosion, poor continuity at connectors and harnesses and/or low incoming voltage.

Conflicting, widely different signals from the three Sensors will cause the ECU to adopt ‘fail safe mode’ as described in the FSM extract, with or without DTC’s. Usually, this will show as widely different Height Control Sensor readings on Techstream or other scanner. In ‘fail safe mode’, AHC operation and TEMS active damping are stopped and poor ride quality is experienced in 'fail safe mode'.

Electrical testing is a ‘must do’ whenever Sensors come off a vehicle AND before installing new Sensors on a vehicle.

Much depends on the correct operation of these Sensors including their connectors and harnesses. It is imperative that they all are reliable. Otherwise, frustration, re-work and wasted time is guaranteed. Height Control Sensor problems are among the most common causes of AHC problems. Depending on the nature of the fault – such as when the Sensor is working but sending an incorrect signal – the Sensor may not throw a Diagnostic Trouble Code (DTC). If in doubt, replace the Sensor.

With ‘cross levelling’ satisfactorily completed AND after fitting tested and reliable Height Control Sensors, it is time to

• adjust the hub-to-fender ‘ride height’ of the vehicle at “N” height, aiming at Front 19.75 inches (500 millimetres), and Rear 20.50 inches (520 millimetres), and also,

• adjust the Height Control Sensors to the correct position (sometimes called the “null position”) in which the Techstream Height Sensor readings are all zero +/- 0.2 inches (or zero +/- 5 millimetres) at “N” height, as specified by FSM. [This corresponds to a signal of about 2.25 volts from the Sensors to the ECU at the “N” height position, as seen in the second FSM extract referenced above. This is the height to which the AHC system is expected to return when “N” is selected at the switch on the centre console, or, when the vehicle is auto-levelling at “N” while in motion. The ECU does this in the background by causing the Levelling Valves and AHC Pump to operate as necessary until the matching ~2.25 volt signal from the Height Control Sensors is found and the required height is achieved with the height switch in “N” position. From this, it can be imagined why the Height Control Sensors and their connectors and harnesses MUST be in good condition for reliable signals and good suspension performance!!]

How to do these two things?

Start the engine, select “N” height at the centre console switch and allow the vehicle to settle.

The Active Test (see last page of the second attachment) can be used to raise the vehicle to the desired height. This involves connecting the pins TS to E1 at DLC1 – this is the receptacle marked DIAGNOSTIC in the engine bay, usually above the Right hand wheel arch. The connector can be an unbent paper clip or similar, nothing special is required. Lights on the dashboard will blink and Techstream will record various faults -- because this connection has the effect of bypassing the controls of the AHC system. This situation will self-correct when the connector is removed later.

When the vehicle is at the required height, turn “OFF” the engine. The Levelling Valves in the Control Valve Assembly will hold the vehicle at this height (assuming all components are healthy) -- unless the engine is turned “ON” again.

Then remove the connector from TS to E1 at DLC1, then turn Ignition Key to “ON” but DO NOT start engine (do not want AHC to attempt auto-levelling during adjustments). If the dashboard AHC light still shows “OFF”, push down on the AHC ON/OFF switch on the centre console to turn “ON” again, select “N” height at the console switch, position the laptop screen so it can be seen using a USB extension cord if that helps, (or use an ELM327 scanner and Bluetooth to a tablet with an app), all doors closed, windows open if desired. (The height selection light in the instrument panel may blink but should show solid green when the adjustments in the next paragraphs are completed).

Then with Ignition Key still "ON", Techstream still "ON", engine still "OFF", and with an eye on the Techstream screen (or other scanner screen) move the sliders on all three proven-healthy Height Control Sensors (two Front, one Rear), one by one, until all Sensor readings are as near as possible to zero, and tighten the locknut. The heim bolts also can be used (front only) but these are very fiddly.

Then pause, check all work so far, drive around the block, re-measure all work, make readjustments as necessary.

With the vehicle now at correct heights front and rear (and only when the vehicle is at correct heights as measured hub-to-fender by tape measure), operate AHC: "N" to "LO" (allow to settle), then "LO" to "N" (allow to settle, ensure pump has stopped after re-charging Height Control Accumulator). Then record AHC pressure readings Front, Rear and Accumulator -- repeat measurements say three times to be sure of reliable readings.

Then turn both of the Torsion Bar adjusters in the same direction until the Front AHC pressure in the correct FSM range is achieved, usually involves about 0.2 Mpa per full turn. The Rear AHC pressure can only be ‘adjusted’ with new OEM springs and spacers or with upgraded springs such as King KTRS-79 if consistent heavy loads or heavy fittings must be considered. The Height Control Accumulator pressure is not adjustable and should be about 10.5 MPa in the pressure test.

Finally, two more points ….

With AHC pressures correct, it is good to check overall 'globe' condition by observing the AHC Tank level at "LO" and at "HI". A difference of 14 graduations indicates that 'globes' are as new; 7 graduations indicates that it is time to replace 'globes'. 'Globes' are 'wear items' and eventually require replacement.

It is good to change the fluid regularly, say every two or three years, so as to better maintain the overall AHC system. This is an easy DIY task, well explained back at Post #1 in this thread and in the video by @suprarx7nut and in several other good IH8MUD threads.

Thank you Indro and rest of all the dedicated members who worked hard to put all this information here. I was overwhelmed but at then end I am pretty happy with what I achieved.

Front left/ right sensor are pretty dialed in at this point. On my tech stream it shows MM instead of inches.
FR sensor 3.4mm (0.13 inches)
FL sensor -2.2mm (-0.08 inches)
Rear sensor -2.0mm (-0.07 inches)
I think they are in the specs.
Front pressure is 7.8
Rear pressure 6.8
Front height left 19.75
Front height right 19.90
Rear left 20.50
Rear right 20.25
I am maxed out on thread for driver side torsion bars. It’s already 1am in Texas so tomorrow will re index driver side torsion bars to lower front pressure sensor.
still have plenty thread left on passenger side torsion bars.
Quick question once AHC settled, I have new wheels and tires ready to go. Should I go for alignment 1st then wheels and tires or install wheels and tires then go for alignment. I am upgrading from 16 to 18 inches wheels.
Thanks again to everyone for help.

 

[Muhammad Rais]

At the time to adjust front pressure sensor do I need to turn of the the engine and AHC off? Or just turn off the engine and put AHC on N height. I am not clear at this step. I know to lower my front pressure sensor I need to CW torsion bars. Please let me know. Thanks.

 

[IndroCruise]

At the time to adjust front pressure sensor do I need to turn of the the engine and AHC off? Or just turn off the engine and put AHC on N height. I am not clear at this step. I know to lower my front pressure sensor I need to CW torsion bars. Please let me know. Thanks.

To answer your question:

1. Set vehicle at desired hub-to-fender heights for “N”,
2. Engine “OFF”,
3. Techstream connected and vehicle Ignition Key “ON” (so that Height Sensor readings can be seen on laptop or scanner screen),
4. Engine remains “OFF” (do not want vehicle to auto-level by starting AHC Pump etc and trying to counter-act your efforts while you are actually making adjustments to each Sensor -- unhelpful and dangerous ),
5. Loosen locknut and move each slider while watching Techstream or other scanner screen, achieve as close to zero reading for Height Sensor on screen as possible,
6. Tighten locknut,
7. Remove Techstream or other scanner,
8. Start engine and test drive vehicle,
9. Return and re-measure hub-to-fender heights for “N” and re-check Height Sensor readings on Techstream,
10. Expect some “fine tuning” as vehicle settles in the new settings and re-adjust until satisfied,

A comment on your numbers in Post #212:

Your numbers in your Post #212 already are very close to specification, except for Front AHC pressure as you already recognise.

It is up to you to decide but further work on vehicle hub-to-fender heights and Sensor readings would be “pursuit of perfection” – and may not be worth the further effort. The AHC and TEMS system should work well when the planned correction is made to Front AHC pressure.

 

[LndXrsr]

Quick question once AHC settled, I have new wheels and tires ready to go. Should I go for alignment 1st then wheels and tires or install wheels and tires then go for alignment. I am upgrading from 16 to 18 inches wheels.

Do your wheels and tires, then get the alignment. Alignment best done after any changes to suspension, wheel/tire, or steering rack rather than before.

 

[uHu]

I am upgrading from 16 to 18 inches wheels.

That's a downgrading. More rim means less rubber. Less rubber means less offroad-worthy.

 

[IndroCruise]

To answer your question:

1. Set vehicle at desired hub-to-fender heights for “N”,
2. Engine “OFF”,
3. Techstream connected and vehicle Ignition Key “ON” (so that Height Sensor readings can be seen on laptop or scanner screen),
4. Engine remains “OFF” (do not want vehicle to auto-level by starting AHC Pump etc and trying to counter-act your efforts while you are actually making adjustments to each Sensor -- unhelpful and dangerous ),
5. Loosen locknut and move each slider while watching Techstream or other scanner screen, achieve as close to zero reading for Height Sensor on screen as possible,
6. Tighten locknut,
7. Remove Techstream or other scanner,
8. Start engine and test drive vehicle,
9. Return and re-measure hub-to-fender heights for “N” and re-check Height Sensor readings on Techstream,
10. Expect some “fine tuning” as vehicle settles in the new settings and re-adjust until satisfied,

A comment on your numbers in Post #212:

Your numbers in your Post #212 already are very close to specification, except for Front AHC pressure as you already recognise.

It is up to you to decide but further work on vehicle hub-to-fender heights and Sensor readings would be “pursuit of perfection” – and may not be worth the further effort. The AHC and TEMS system should work well when the planned correction is made to Front AHC pressure.

Here are some pictures which may help ....

 

[Muhammad Rais]

Here is the new screenshots after reindex torsion bars on the driver side. It took some time to fine tune it but I think it’s within the specs or close to it. Way better than originally started so overall I am really happy. Hopefully will flush AHC fluid soon.

All 3 of height control sensors are in .0 inches versus mm.
.4 mm= 0.01 inches
.6 mm= 0.02 inches
-1 mm= -0.03 inches
Front heights are very close to 20 inches and rear is 20.75.
Also checked graduations in the tank and found 8 which is acceptable
Accumulator pressure sensor 10.5
Yes now I can tell through all your hard work I also know how AHC works.
will flush AHC fluid soon.
to all the members who put this information together and helped me to understand and tackle this issue on my car, I am great full to you all.
Thanks. Have a blessed day.

 

[IndroCruise]

Here is the new screenshots after reindex torsion bars on the driver side. It took some time to fine tune it but I think it’s within the specs or close to it. Way better than originally started so overall I am really happy. Hopefully will flush AHC fluid soon.
View attachment 2683830


All 3 of height control sensors are in .0 inches versus mm.
.4 mm= 0.01 inches
.6 mm= 0.02 inches
-1 mm= -0.03 inches
Front heights are very close to 20 inches and rear is 20.75.
Also checked graduations in the tank and found 8 which is acceptable
Accumulator pressure sensor 10.5
Yes now I can tell through all your hard work I also know how AHC works.
will flush AHC fluid soon.
to all the members who put this information together and helped me to understand and tackle this issue on my car, I am great full to you all.
Thanks. Have a blessed day.

Great outcome, well done!!

There was some trial and error while learning at the start (as we all did), then successfully followed correct sequence under standard FSM-specified conditions:

1. Equalised tape-measured Front ‘cross-level’ hub-to-fender heights using Torsion Bar adjusters,
2. Adjusted tape-measured ‘Ride heights’ to IH8MUD recommendations at "N" height by Height Control Sensor adjusters,
3. Adjusted Height Sensors to near-zero reading on Techstream at "N" height,
4. Adjusted Front AHC pressure Torsion Bar adjusters to give Front AHC pressure on Techstream per FSM specification at "N" height, including re-indexing of Torsion Bars,
5. Checked Rear AHC pressure on Techstream per FSM specification at "N" height,
6. Accumulator pressure checked against expectation of ~10.5 Mpa (although not showing on Techstream),
7. Checked overall ‘globe’ condition against FSM specification per differences in HI to LO graduations at AHC Tank,

Changing AHC Fluid will complete the project.

Techstream is still showing one DTC -- fluid temperature showing -30degC, so maybe due to disconnected Temperature Sensor during Rear AHC pressure measurement?

 

[Muhammad Rais]

Temperature sensor was unplugged per post #1. After driving for a bit I will recheck everything just to make sure. Now I know torsion bar doesn’t raise heights for AHC equipped vehicle.