Definitive list of AHC maintenance items (7 Viewers)

[2manycruisers]

This seems to have become the go-to AHC troubleshooting thread, but let me know if I'm in the wrong place.
I have a 2000 LX470 with 230k miles. In the spring I replaced the rear coils with new OEM and adjusted torsion bars and IIRC, the rig was within or close to spec front and rear. I've added some weight and on a recent trip overloaded the AHC so I decided to add coil spacers today. I probably didn't disconnect enough things and have caused a problem. I started with the vehicle in H, not N. I disconnected only the sway bar and lower shock/ram mount to add the spacers. I may have stretched, bent, disconnected, or otherwise damaged something because now the rear appears to be in the L height, the dash shows N, and the AHC "OFF" light is flashing. If I press the AHC up or down, they flash a couple times then stay put.

I have to do some work on my computer to get access back to TechStream, I forgot a password. I did read (after my failure) that there is a risk of rear height sensor damage when replacing coils or adding spacers, but I didn't find information on what kind of damage or how to check for it. Any thoughts on what I damaged or what I need to look for in TechStream when I get it up again?
Thanks!

 

[ramangain]

Did you drop the axle just enough to safely remove the springs, or way more than necessary? You probably mangled the r da r height sensor, or if you are lucky you may just have to reconnect it

 

[IndroCruise]

This seems to have become the go-to AHC troubleshooting thread, but let me know if I'm in the wrong place.
I have a 2000 LX470 with 230k miles. In the spring I replaced the rear coils with new OEM and adjusted torsion bars and IIRC, the rig was within or close to spec front and rear. I've added some weight and on a recent trip overloaded the AHC so I decided to add coil spacers today. I probably didn't disconnect enough things and have caused a problem. I started with the vehicle in H, not N. I disconnected only the sway bar and lower shock/ram mount to add the spacers. I may have stretched, bent, disconnected, or otherwise damaged something because now the rear appears to be in the L height, the dash shows N, and the AHC "OFF" light is flashing. If I press the AHC up or down, they flash a couple times then stay put.

I have to do some work on my computer to get access back to TechStream, I forgot a password. I did read (after my failure) that there is a risk of rear height sensor damage when replacing coils or adding spacers, but I didn't find information on what kind of damage or how to check for it. Any thoughts on what I damaged or what I need to look for in TechStream when I get it up again?
Thanks!

Assuming that you have replaced like-for-like OEM rear springs and more recently added the common 30 millimetre spacers or similar, and that there is no obvious mechanical impediment to the vehicle dropping to “LO” when switched or rising to “HI” when switched (if the AHC system were free of faults), then ….

As you probably know, there is only one Rear Height Control Sensor and it is attached to a chassis cross-member slightly forward and to the left of the rear differential. A link from this Sensor then connects to an attachment on the Left Rear Upper Control Arm. In this way, movement of the chassis and body relative to the rear axle is measured. If the chassis is rigid and undamaged and all suspension components front and rear are in good order, including and especially the front Height Control Sensors, then one rear Sensor is all that is necessary.

It is possible that the linkage at the Rear Sensor has become damaged or the sliding adjuster has slipped during other suspension work.

It is easier to see the situation while under the vehicle with the spare wheel removed and out of the way.

PRECAUTION: Put stands under the chassis rails so that there is no chance of any strange AHC event causing the vehicle to descend on you while working under the vehicle!

It is worthwhile to inspect the Sensor and its mechanical linkage and attachment to the Left Rear Upper Control Arm AND the electrical connector. Any damage to mechanical parts will be obvious. For comparison, the attached pics show my recently installed new Rear Sensor, fresh out of the box.

The sensors (Front as well as Rear) are simple and robust potentiometers. If original, these Sensors have been living for 20 years on your vehicle in the most hostile environment known to man – through cycles of heat, cold, humidity, stream crossings, beach adventures, road spray, mud, snow, sand, salt, sticks, stones etc, etc.

If these Sensors have not been part of the reliability maintenance program for the vehicle over the last 20 years, then ‘surprises’ WILL occur.

Height Control Sensor faults may or may not show up as Diagnostic Trouble Codes (DTC’s) on Techstream or other scanner but various ‘fail safe’ symptoms will be experienced as set out in the DIAGNOSTICS section of the FSM. This lengthy FSM reference is worthwhile reading – best not to be too distracted too soon by all the circuit diagrams but follow the logic of the diagnostic process and especially the Problems Symptoms Table.

In any case, whether mechanically damaged or not, it is worth removing the Sensor and linkage for testing and external and internal examination. This is straightforward:

First, mark the position of the bolt at the sliding adjuster so that you know where things were. Undo two bolts at the chassis, one nut at the linkage, one cable clip and one electrical connector and remove the connector. Break out the multimeter and three 1.5 volt batteries (to simulate applied voltage when the Sensor is in use), have a quick read of the simple FSM test procedure and some IH8MUD posts by searching “Height Control Sensors”.

Remove the rear cover – four Philips head screws – and inspect for corrosion of the internal spring-like connectors and their seats and for wear or breaks in the carbon tracks or the tiny brushes. Clean up, re-assemble, re-test and re-install, or if in doubt, replace.

If the connecting tab on the Upper Control Arm has been damaged, repair as necessary.

Before re-installation, use a multimeter to test continuity and voltage at the Sensor plug on the harness on the vehicle.

When the refurbished (or replacement) Sensor is installed, go through the whole process of re-setting the vehicle heights and doing the basic checks of the AHC system, all in the correct sequence:

1. Cross-level front with engine “OFF” – use torsion bar adjusters, NOT height sensor adjusters,
2. Measure all hub-to-fender distances with engine “ON” – front 19.75 inches, rear 20.50 inches. Adjust as necessary with Height Control Sensor adjusters, NOT torsion bar adjusters,
3. With hub-to-fender operating distances correct, check front and rear AHC pressures with the Techstream or other scanner. Adjust as necessary with torsion bar adjusters, NOT Height Control Sensor Adjusters,
4. With both hub-to-fender operating distances correct AND AHC pressures correct, check overall ‘globe’ condition – drop vehicle to “LO” observe and mark AHC fluid level at AHC tank in engine bay, raise vehicle to “HI” and observe and mark AHC fluid level at AHC tank – looking for much better than 8 graduations difference if ‘globes’ overall are healthy.

It is also recommended that the opportunity be taken to check the physical condition and electrical health of BOTH Front Height Control Sensors at this time.

Late edit with further background information:

It is possible that there are other more complicated (but less likely) causes of the symptoms you describe rather than a Height Control Sensor problem -- for example a faulty Control Valve Assembly or problems at the AHC Electronic Control Unit (ECU). However, problems with Height Control Sensors are more likely and are the orderly place to start. If they are healthy, correctly adjusted but the problem persists, then the recommendation is to avoid guessing and methodically work through the Problems Symptoms Table in the AHC DIAGNOSTIC section of the FSM -- see attachment to the link in my para 8 above.

The two general and well-illustrated links below concerning Height Control Sensor condition may be helpful.

A very unhappy Rear Height Control Sensor – with pictures from @Azi

Two posts with more explanation – with pictures from @uHu

Pictures show my new Rear Height Control Sensor installed:

 

[2manycruisers]

Great information, thank you! Just that picture would have solved the problem for me. When I lowered the axle to add the coils, the linkage inverted. So all the way compressed, the eco was reading that it was 5.5" high. That's fixed, now I need to find the proper height measurement so I can adjust it.
As an aside, I took the sensor off and opened it up to check for damage and it looks brand new inside. No moisture or corrosion at all. Happy with that.

 

[2manycruisers]

Did you drop the axle just enough to safely remove the springs, or way more than necessary? You probably mangled the r da r height sensor, or if you are lucky you may just have to reconnect it

As you see above, I did mangle the sensor linkage. FWIW, I didn't drop the axle way more than necessary, or any more than necessary for that matter, at least to do it without a coil spring compressor. I still had to pry the springs into place on both sides with the spacers on them.

 

[IndroCruise]

Great information, thank you! Just that picture would have solved the problem for me. When I lowered the axle to add the coils, the linkage inverted. So all the way compressed, the eco was reading that it was 5.5" high. That's fixed, now I need to find the proper height measurement so I can adjust it.
As an aside, I took the sensor off and opened it up to check for damage and it looks brand new inside. No moisture or corrosion at all. Happy with that.

Good that all was easily fixed. Hub-to-fender distances with engine and AHC “ON” should be front 19.75 inches, rear 20.50 inches physically measured by tape – this is the IH8MUD practical approximation of the very finicky actual height measurement procedure set out in the FSM. When the engine and AHC are operating and these tape measurements have been achieved then the height sensor readings on Techstream or other scanner should read close to zero – FSM specifies +/- 5 millimetres (0.20 inches). If not, there is a problem with the one or more height control sensors (even if they look good) or there are some deeper problems* in the AHC system. If the height sensor readings are wildly different from one another, then the ECU will adopt one of its ‘fail safe’ modes – most likely the one described in the FSM as “Fail safe function: If a trouble occurs in the height control sensor circuit, the height control is prohibited after the ECU has adjusted the vehicle height to the standard (fluid pressure correspond to the standard height)”. The language loses a bit in the Japanese to English translation – but the effect described also means that the 16-step variable damping has been shut down and this is experienced as a ‘rough ride’. This is particularly evident at low speed over minor bumps in the road because in this so-called ‘fail safe’ condition the step motors in the Damping Force Control Actuators (to which the ‘globes’ are attached) remain at Step 8 and the system prevents a softer damping position being adopted.

* See this link for ‘Deeper problems’ in the AHC system.

Hope none of the above occurs and that all goes well!

 

[2manycruisers]

Good that all was easily fixed. Hub-to-fender distances with engine and AHC “ON” should be front 19.75 inches, rear 20.50 inches physically measured by tape – this is the IH8MUD practical approximation of the very finicky actual height measurement procedure set out in the FSM. When the engine and AHC are operating and these tape measurements have been achieved then the height sensor readings on Techstream or other scanner should read close to zero – FSM specifies +/- 5 millimetres (0.20 inches). If not, there is a problem with the one or more height control sensors (even if they look good) or there are some deeper problems* in the AHC system. If the height sensor readings are wildly different from one another, then the ECU will adopt one of its ‘fail safe’ modes – most likely the one described in the FSM as “Fail safe function: If a trouble occurs in the height control sensor circuit, the height control is prohibited after the ECU has adjusted the vehicle height to the standard (fluid pressure correspond to the standard height)”. The language loses a bit in the Japanese to English translation – but the effect described also means that the 16-step variable damping has been shut down and this is experienced as a ‘rough ride’. This is particularly evident at low speed over minor bumps in the road because in this so-called ‘fail safe’ condition the step motors in the Damping Force Control Actuators (to which the ‘globes’ are attached) remain at Step 8 and the system prevents a softer damping position being adopted.

* See this link for ‘Deeper problems’ in the AHC system.

Hope none of the above occurs and that all goes well!

That is great information to watch for. Once I flipped the linkage it sat about 3” high in the back and Techstream said it was at 0”. Not only did I bend the linkage mount on the UCA, I also bent the sensor mount on the body. While engine was running, I bent the sensor mount on the body (just hand pressure) until I measured 20.5" at the fender well. I think all is good now.
Interestingly, I would go L-N-H-L-N, etc through the heights and check the readings and measurements. Neutral pressures were 6.1 front and 7.0 rear, then suddenly the front dropped to 2.6 and stayed there through several height changes. I went for a short drive and it came back to 6.8 and 7.0. I wish I had been able to read my neutral pressures before the coil spacers, I thought it would be lower than that.

 

[EPTX]

Here are my results in an attempt to get the AHC to spec:

Vehicle: 2000 LX470 with 170k miles, all original components. I bought it 2 months ago.
OEM Specs:
Front Pressure Sensor: 6.9 +- 0.5 (6.4 - 7.3)
Rear Pressure Sensor: 5.7 +- 0.3 (5.4 - 6.0)
Fluid Reservoir Gradations: Min 7.0

My LX Specs (start):
Gradations: 9
FL Hub-to-Fender: 19" (low)
FR Hub-to-Fender: 18 3/4" (low)
RL Hub-to-Fender: 19" (low)
RR Hub-to-Fender: 19 3/8" (low)
F Pressure Sensor: 7.0 (in spec)
R Pressure Sensor: 6.9 (high)
Measurements taken with: F/R bumpers: Stock. Roof: Stock. Steps: removed. 3rd Row Seats: Removed. Gas: Full Tank. Did NOT remove the AHC Temp Sensor.

GOAL: Get Hub-to-Fender heights in spec AND pressures on low end of spec range to relieve stress on aging globes
Front Pressure Sensor (target): 6.4
Front Hub-to-Fender (target): 19 3/4"
Rear Pressure Sensor (target): 5.4
Rear Hub-to-Fender (target): 20 1/2"

Pass 1: Get front R and L level AND to 19 3/4"
FL Hub-to-Fender: 19 3/8" (close enough for now), +1 turns on TB
FR Hub-to-Fender: 19 3/8" (close enough for now), +2.5 turns on TB
RL Hub-to-Fender: should have re-measured
RR Hub-to-Fender: should have re-measured
F Pressure Sensor: 6.0 (out of spec AND low to target)
R Pressure Sensor: 6.0 (in spec BUT high to target)

Pass 2: Flush AHC Fluid (goal to see what changes fresh fluid made)
FL Hub-to-Fender: no change
FR Hub-to-Fender: no change
RL Hub-to-Fender: should have re-measured
RR Hub-to-Fender: should have re-measured
F Pressure Sensor: 6.3 (out of spec AND low to target) *I was expecting pressures to drop, maybe because I didn't drive between tests? Noticeable ride improvement*
R Pressure Sensor: 6.2 (out of spec AND high to target) *I was expecting pressures to drop, maybe because I didn't drive between tests? Noticeable ride improvement*

Pass 3: Add Ironman 30mm Spring Spacers to Rear (goal to get rear pressures lower)
FL Hub-to-Fender: no change
FR Hub-to-Fender: no change
RL Hub-to-Fender: 21 1/2" (out of spec AND high to target)
RR Hub-to-Fender: 21 1/2" (out of spec AND high to target)
F Pressure Sensor: 6.3 (in spec BUT low to target)
R Pressure Sensor: 6.0 (in spec BUT high to target) *I was expecting a 0.5 drop but only saw a 0.2 drop*

Pass 4: Adjusted rear height sensor, lowered bolt to max (goal to get rear pressures lower AND height in target range)
FL Hub-to-Fender: no change
FR Hub-to-Fender: no change
RL Hub-to-Fender: 19 3/4" (out of spec AND low to target)
RR Hub-to-Fender: 19 3/4" (out of spec AND low to target)
F Pressure Sensor: 6.4 (right on target)
R Pressure Sensor: 5.7 (high to target but I'm at the max range on height sensor)

SUMMARY

1. Front:
Front Pressure Sensor (target): 6.4. RESULT: 6.4
Front Hub-to-Fender (target): 19 3/4". RESULT: 19 3/8"
Future Changes: None, I'm happy with where it landed

2. Rear:
Rear Pressure Sensor (target): 5.4. RESULT: 5.7
Rear Hub-to-Fender (target): 20 1/2". RESULT: 19 3/4"
Future Changes: Would like to keep pressures at 5.4 but get Hub-to-Fender height to spec of 20 1/2". Will replace springs and 30mm spacers with new OEM LX Springs (or possibly King Springs).

HELP
If anyone has new or low mileage OEM LX springs, OR King Spring KTRS-79, I need to buy some! I'll post the results here so everyone can see the results.

 

[IndroCruise]

Here are my results in an attempt to get the AHC to spec:

Vehicle: 2000 LX470 with 170k miles, all original components. I bought it 2 months ago.
OEM Specs:
Front Pressure Sensor: 6.9 +- 0.5 (6.4 - 7.3)
Rear Pressure Sensor: 5.7 +- 0.3 (5.4 - 6.0)
Fluid Reservoir Gradations: Min 7.0

My LX Specs (start):
Gradations: 9
FL Hub-to-Fender: 19" (low)
FR Hub-to-Fender: 18 3/4" (low)
RL Hub-to-Fender: 19" (low)
RR Hub-to-Fender: 19 3/8" (low)
F Pressure Sensor: 7.0 (in spec)
R Pressure Sensor: 6.9 (high)
Measurements taken with: F/R bumpers: Stock. Roof: Stock. Steps: removed. 3rd Row Seats: Removed. Gas: Full Tank. Did NOT remove the AHC Temp Sensor.

GOAL: Get Hub-to-Fender heights in spec AND pressures on low end of spec range to relieve stress on aging globes
Front Pressure Sensor (target): 6.4
Front Hub-to-Fender (target): 19 3/4"
Rear Pressure Sensor (target): 5.4
Rear Hub-to-Fender (target): 20 1/2"

Pass 1: Get front R and L level AND to 19 3/4"
FL Hub-to-Fender: 19 3/8" (close enough for now), +1 turns on TB
FR Hub-to-Fender: 19 3/8" (close enough for now), +2.5 turns on TB
RL Hub-to-Fender: should have re-measured
RR Hub-to-Fender: should have re-measured
F Pressure Sensor: 6.0 (out of spec AND low to target)
R Pressure Sensor: 6.0 (in spec BUT high to target)

Pass 2: Flush AHC Fluid (goal to see what changes fresh fluid made)
FL Hub-to-Fender: no change
FR Hub-to-Fender: no change
RL Hub-to-Fender: should have re-measured
RR Hub-to-Fender: should have re-measured
F Pressure Sensor: 6.3 (out of spec AND low to target) *I was expecting pressures to drop, maybe because I didn't drive between tests? Noticeable ride improvement*
R Pressure Sensor: 6.2 (out of spec AND high to target) *I was expecting pressures to drop, maybe because I didn't drive between tests? Noticeable ride improvement*

Pass 3: Add Ironman 30mm Spring Spacers to Rear (goal to get rear pressures lower)
FL Hub-to-Fender: no change
FR Hub-to-Fender: no change
RL Hub-to-Fender: 21 1/2" (out of spec AND high to target)
RR Hub-to-Fender: 21 1/2" (out of spec AND high to target)
F Pressure Sensor: 6.3 (in spec BUT low to target)
R Pressure Sensor: 6.0 (in spec BUT high to target) *I was expecting a 0.5 drop but only saw a 0.2 drop*

Pass 4: Adjusted rear height sensor, lowered bolt to max (goal to get rear pressures lower AND height in target range)
FL Hub-to-Fender: no change
FR Hub-to-Fender: no change
RL Hub-to-Fender: 19 3/4" (out of spec AND low to target)
RR Hub-to-Fender: 19 3/4" (out of spec AND low to target)
F Pressure Sensor: 6.4 (right on target)
R Pressure Sensor: 5.7 (high to target but I'm at the max range on height sensor)

SUMMARY

1. Front:
Front Pressure Sensor (target): 6.4. RESULT: 6.4
Front Hub-to-Fender (target): 19 3/4". RESULT: 19 3/8"
Future Changes: None, I'm happy with where it landed

2. Rear:
Rear Pressure Sensor (target): 5.4. RESULT: 5.7
Rear Hub-to-Fender (target): 20 1/2". RESULT: 19 3/4"
Future Changes: Would like to keep pressures at 5.4 but get Hub-to-Fender height to spec of 20 1/2". Will replace springs and 30mm spacers with new OEM LX Springs (or possibly King Springs).

HELP
If anyone has new or low mileage OEM LX springs, OR King Spring KTRS-79, I need to buy some! I'll post the results here so everyone can see the results.

At Pass 4, you mention that you “Adjusted rear height sensor, lowered bolt to max (goal to get rear pressures lower AND height in target range)”

Apologies if I have misunderstood your meaning.

Also, unless I have misunderstood something, my reading of the FSM suggests that your correct rear AHC pressures may be 5.6 MPa to 6.7 Mpa “without rear sub-tank” and “using hand-held tester”. Could it be that inadvertently you may have been looking at a specified pressure range which is applicable to use of a pressure gauge?

By the way, some IH8MUD Members report significant differences in rear AHC pressure readings when the temperature sensor is disconnected per FSM. Others observe little if any difference. However, there must be a reason why this precaution has been included in the FSM even though no explanation is offered.

FSM reference for the above matters:
https://lc100e.github.io/manual/
then tabs in index panel
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM > ON-VEHICLE INSPECTION
Pages SA-308 to SA-309

My explanation relates to the attached pictures.

Late edit to correct these two statements:
If you lower the adjuster bolt at the Rear Height Control Sensor adjuster, the rear AHC pressure will increase and the rear height will decrease.

To reduce the rear AHC pressure the adjuster bolt would need to be raised. However, this will increase the rear height of the vehicle.

If you slide the adjuster bolt down at the Rear Height Control Sensor adjuster, the rear AHC pressure will decrease and the rear height will decrease.

To increase the rear AHC pressure the adjuster bolt would need to slide upwards. This also will increase the rear height of the vehicle.

Some IH8MUD Members write about their efforts to achieve a “sensor lift” with some noting that up to one inch height increase at the rear does not have significant effect on front end geometry. This causes an increase in rear AHC pressure.

In my own case, I did not use spacers but I replaced the OEM rear springs with KING KTRS-79 springs.

As expected, the higher spring rate resulted in a lower rear AHC pressure when the vehicle is in an unloaded condition, in my case measuring around 5.7 MPa at standard rear height.

This works very well when the vehicle is loaded for long distance travels. The additional load causes increased rear AHC pressures within specification but still at the low end of range and with very good ride quality.

When the vehicle is not loaded – basically empty – the ride is acceptable but, as expected, not as good as in the loaded condition.

To find the best compromise, I have been “tuning” the suspension by shortening raising the bolt position at the rear Height Control Sensor adjuster as shown in the picture. The mark on the slider shows the original position of the bolt on the slider. This raised the vehicle slightly and gave a corresponding increase in the rear AHC pressure, currently at 5.9 Mpa with rear hub-to-fender height of 21 inches on both sides. I will experiment with this a little further.

In your case, you also could try slightly higher rear heights to find the desired rear AHC pressures. The configuration of your vehicle is slightly different to my vehicle which carries 141 litres (37 US gallons) of diesel fuel when both tanks are full and so my correct rear AHC pressure range is 5.9 to 7.0 Mpa per FSM “with sub fuel tank “ and “using hand-held tester”.

 

[IndroCruise]

At Pass 4, you mention that you “Adjusted rear height sensor, lowered bolt to max (goal to get rear pressures lower AND height in target range)”

Apologies if I have misunderstood your meaning.

Also, unless I have misunderstood something, my reading of the FSM suggests that your correct rear AHC pressures may be 5.6 MPa to 6.7 Mpa “without rear sub-tank” and “using hand-held tester”. Could it be that inadvertently you may have been looking at a specified pressure range which is applicable to use of a pressure gauge?

By the way, some IH8MUD Members report significant differences in rear AHC pressure readings when the temperature sensor is disconnected per FSM. Others observe little if any difference. However, there must be a reason why this precaution has been included in the FSM even though no explanation is offered.

FSM reference for the above matters:
https://lc100e.github.io/manual/
then tabs in index panel
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM > ON-VEHICLE INSPECTION
Pages SA-308 to SA-309

My explanation relates to the attached pictures.

Late edit to correct these two statements:
If you lower the adjuster bolt at the Rear Height Control Sensor adjuster, the rear AHC pressure will increase and the rear height will decrease.

To reduce the rear AHC pressure the adjuster bolt would need to be raised. However, this will increase the rear height of the vehicle.

If you slide the adjuster bolt down at the Rear Height Control Sensor adjuster, the rear AHC pressure will decrease and the rear height will decrease.

To increase the rear AHC pressure the adjuster bolt would need to slide upwards. This also will increase the rear height of the vehicle.

Some IH8MUD Members write about their efforts to achieve a “sensor lift” with some noting that up to one inch height increase at the rear does not have significant effect on front end geometry.

In my own case, I did not use spacers but I replaced the OEM rear springs with KING KTRS-79 springs.

As expected, the higher spring rate resulted in a lower rear AHC pressure when the vehicle is in an unloaded condition, in my case measuring around 5.7 MPa at standard rear height.

This works very well when the vehicle is loaded for long distance travels. The additional load causes increased rear AHC pressures within specification but still at the low end of range and with very good ride quality.

When the vehicle is not loaded – basically empty – the ride is acceptable but, as expected, not as good as in the loaded condition.

To find the best compromise, I have been “tuning” the suspension by shortening raising the bolt position at the rear Height Control Sensor adjuster as shown in the picture. The mark on the slider shows the original position of the bolt on the slider. This raised the vehicle slightly and gave a corresponding increase in the rear AHC pressure, currently at 5.9 Mpa with rear hub-to-fender height of 21 inches on both sides. I will experiment with this a little further.

In your case, you also could try slightly higher rear heights to find the desired rear AHC pressures. The configuration of your vehicle is slightly different to my vehicle which carries 141 litres (37 US gallons) of diesel fuel when both tanks are full and so my correct rear AHC pressure range is 5.9 to 7.0 Mpa per FSM “with sub fuel tank “ and “using hand-held tester”.

View attachment 2466521

View attachment 2466522

LATE EDIT TO PREVIOUS POST #829:

For good order I should have repeated the usual SAFETY WARNING and additional information for the benefit of any reader:

NEVER physically actually adjust the Height Control Sensor adjusters (or even the Torsion Bar adjusters) while person parts are under the vehicle or in the wheel arches, and especially under the rear Height Control Sensor adjuster, when the engine/AHC is “ON”, unless vehicle stands are in place to prevent major movements.

Deliberate or inadvertent changes while the engine/AHC is “ON” could result in the vehicle descending quickly onto the person, causing injury. Best if the engine/AHC are “OFF” and the keys are in your pocket so that the AHC system is “LOCKED OFF”. Second best – put stands in place to prevent excessive movement of the vehicle and protect the person. Be wary of exhaust fumes and the poisonous effects of carbon monoxide.

After any adjustment and when checking the measurements of the ‘operating ride heights’ (Target Front: 19.75 inches or 500mm, and, Target Rear: 20.50 inches or 520mm), the engine/AHC should be “ON” following the N >> LO >> N height change to check AHC pressures.

The purposes are to measure both the pressures and the 'operating ride heights' under the same conditions because one affects the other.

For the same reason, the following sequence is recommended when making AHC adjustments and is consistent with the FSM:

1. If necessary, correct front ‘cross-level’ using Torsion Bar adjusters, usually by turning opposite sides in equal but opposite directions to achieve equal hub-to-fender measurements (Note: this is about equalising loadings on both torsion bars, nothing to do with ‘operating ride heights’),
2. Set ‘operating ride heights’ using Height Control Sensor adjusters (not Torsion Bar adjusters) – check with engine/AHC “ON” and suspension settled, but make actual adjustments with engine/AHC “OFF” for safety,
3. When ‘operating ride heights’ are correct, check front and rear AHC neutral pressures,
4. If necessary, adjust front AHC pressures by turning both torsion bar adjusters equal amounts in the same direction – clockwise to increase load on torsion bars and reduce front AHC pressure, counterclockwise to reduce load on torsion bars and increase front AHC pressure,
5. If necessary, correct excessive rear pressures with new springs and/or spacers or higher rated springs such as KING KTRS-79,
6. When 'operating ride heights' and the front and rear neutral pressures are correct, then at the time of the AHC neutral pressure readings on Techstream or other scanner, the Height Sensor readings should be close to zero (provided Sensors are healthy),
7. When AHC neutral pressures are correct (which means ‘operating ride heights’ also are correct), check overall ‘globe’ condition by observing AHC tank level at “LO” suspension height compared with AHC tank level at “HI” suspension height. Difference of ~14 means 'as new', difference of ~7 means time to replace globes [NOTE: AHC Pressures tells NOTHING about the condition of the 'globes'],
8. Fine tune the settings by repeating Step 1 to Step 7 until results are satisfactory,
9. If faults persist, then it is time to work through the "Diagnostics" section of the FSM,
10. The systematic approach set out in the FSM rather than guesswork is advisable but early suspicion of faulty Height Control Sensors or their harness connections are forgiveable.

Note that the target ‘operating ride heights’ mentioned above have been widely adopted within IH8MUD and are considered reliable when correctly done. They are considered to be a good approximation of the more detailed method given in the FSM. These target heights do not come from Toyota nor Lexus and are not found in the FSM.

FSM reference for adjusting Height Control Sensor adjusters to achieve required ‘operating ride heights’:
https://lc100e.github.io/manual/
then tabs in index panel
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM > ADJUSTMENT
Pages SA-313 to SA-319

FSM reference for on-vehicle inspection of overall condition of ‘globes’ (Gas Chambers):
https://lc100e.github.io/manual/
then tabs in index panel
Repair Manual > SUSPENSION AND AXLE > DAMPING FORCE CONTROL ACTUATOR > ON-VEHICLE INSPECTION
Page SA-338

FSM reference for AHC DIAGNOSTICS:
https://lc100e.github.io/manual/
then tabs in index panel
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION
There are multiple items – see
HOW TO PROCEED WITH TROUBLESHOOTING
DIAGNOSTIC TROUBLE CODE (DTC) CHART
PROBLEM SYMPTOMS TABLE
Example: C1711/11 to C1713/13 Height Control Sensor Circuit

Note the ‘fail safe’ function in this case. (There are also several other 'fail safe' functions associated with other faults):

Quote from FSM: “If a trouble occurs in the height control sensor circuit, the height control is prohibited after the ECU has adjusted the vehicle height to the standard (fluid pressure corresponds to the standard height”.

Translation of the Symptom: The AHC system and the TEMS system may not work properly, variable damping may cease because the AHC Electronic Control Unit (ECU) may lock the Damping Force Control Actuators into setting no. 8 of 16 settings. 'Rough ride' may then be experienced, especially at low speeds.

Moral of this part of the story: When all else is good but problems continue, be suspicious of Height Control Sensors and connections to the harness, especially in the case of older vehicles and where adverse environments and corrosion may be present.

When certain of healthy Height Control Sensors and connections and if problems still persist, work through other items in the order given in the FSM Problem Symptoms Table. Note that sometimes DTC's do not appear, or may be difficult to interpret. In such cases, try to identify the problem by thinking through the symptoms.

 

[IndroCruise]

LATE EDIT TO PREVIOUS POST #829:

For good order I should have repeated the usual SAFETY WARNING and additional information for the benefit of any reader:

NEVER physically actually adjust the Height Control Sensor adjusters (or even the Torsion Bar adjusters) while person parts are under the vehicle or in the wheel arches, and especially under the rear Height Control Sensor adjuster, when the engine/AHC is “ON”, unless vehicle stands are in place to prevent major movements.

Deliberate or inadvertent changes while the engine/AHC is “ON” could result in the vehicle descending quickly onto the person, causing injury. Best if the engine/AHC are “OFF” and the keys are in your pocket so that the AHC system is “LOCKED OFF”. Second best – put stands in place to prevent excessive movement of the vehicle and protect the person. Be wary of exhaust fumes and the poisonous effects of carbon monoxide.

After any adjustment and when checking the measurements of the ‘operating ride heights’ (Target Front: 19.75 inches or 500mm, and, Target Rear: 20.50 inches or 520mm), the engine/AHC should be “ON” following the N >> LO >> N height change to check AHC pressures.

The purposes are to measure both the pressures and the 'operating ride heights' under the same conditions because one affects the other.

For the same reason, the following sequence is recommended when making AHC adjustments and is consistent with the FSM:

1. If necessary, correct front ‘cross-level’ using Torsion Bar adjusters, usually by turning opposite sides in equal but opposite directions to achieve equal hub-to-fender measurements (Note: this is about equalising loadings on both torsion bars, nothing to do with ‘operating ride heights’),
2. Set ‘operating ride heights’ using Height Control Sensor adjusters (not Torsion Bar adjusters) – check with engine/AHC “ON” and suspension settled, but make actual adjustments with engine/AHC “OFF” for safety,
3. When ‘operating ride heights’ are correct, check front and rear AHC neutral pressures,
4. If necessary, adjust front AHC pressures by turning both torsion bar adjusters equal amounts in the same direction – clockwise to increase load on torsion bars and reduce front AHC pressure, counterclockwise to reduce load on torsion bars and increase front AHC pressure,
5. If necessary, correct excessive rear pressures with new springs and/or spacers or higher rated springs such as KING KTRS-79,
6. When 'operating ride heights' and the front and rear neutral pressures are correct, then at the time of the AHC neutral pressure readings on Techstream or other scanner, the Height Sensor readings should be close to zero (provided Sensors are healthy),
7. When AHC neutral pressures are correct (which means ‘operating ride heights’ also are correct), check overall ‘globe’ condition by observing AHC tank level at “LO” suspension height compared with AHC tank level at “HI” suspension height. Difference of ~14 means 'as new', difference of ~7 means time to replace globes [NOTE: AHC Pressures tells NOTHING about the condition of the 'globes'],
8. Fine tune the settings by repeating Step 1 to Step 7 until results are satisfactory,
9. If faults persist, then it is time to work through the "Diagnostics" section of the FSM,
10. The systematic approach set out in the FSM rather than guesswork is advisable but early suspicion of faulty Height Control Sensors or their harness connections are forgiveable.

Note that the target ‘operating ride heights’ mentioned above have been widely adopted within IH8MUD and are considered reliable when correctly done. They are considered to be a good approximation of the more detailed method given in the FSM. These target heights do not come from Toyota nor Lexus and are not found in the FSM.

FSM reference for adjusting Height Control Sensor adjusters to achieve required ‘operating ride heights’:
https://lc100e.github.io/manual/
then tabs in index panel
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM > ADJUSTMENT
Pages SA-313 to SA-319

FSM reference for on-vehicle inspection of overall condition of ‘globes’ (Gas Chambers):
https://lc100e.github.io/manual/
then tabs in index panel
Repair Manual > SUSPENSION AND AXLE > DAMPING FORCE CONTROL ACTUATOR > ON-VEHICLE INSPECTION
Page SA-338

FSM reference for AHC DIAGNOSTICS:
https://lc100e.github.io/manual/
then tabs in index panel
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION
There are multiple items – see
HOW TO PROCEED WITH TROUBLESHOOTING
DIAGNOSTIC TROUBLE CODE (DTC) CHART
PROBLEM SYMPTOMS TABLE
Example: C1711/11 to C1713/13 Height Control Sensor Circuit

Note the ‘fail safe’ function in this case. (There are also several other 'fail safe' functions associated with other faults):

Quote from FSM: “If a trouble occurs in the height control sensor circuit, the height control is prohibited after the ECU has adjusted the vehicle height to the standard (fluid pressure corresponds to the standard height”.

Translation of the Symptom: The AHC system and the TEMS system may not work properly, variable damping may cease because the AHC Electronic Control Unit (ECU) may lock the Damping Force Control Actuators into setting no. 8 of 16 settings. 'Rough ride' may then be experienced, especially at low speeds.

Moral of this part of the story: When all else is good but problems continue, be suspicious of Height Control Sensors and connections to the harness, especially in the case of older vehicles and where adverse environments and corrosion may be present.

When certain of healthy Height Control Sensors and connections and if problems still persist, work through other items in the order given in the FSM Problem Symptoms Table. Note that sometimes DTC's do not appear, or may be difficult to interpret. In such cases, try to identify the problem by thinking through the symptoms.

Errors have been edited and corrected in my previous posts #829 and #830 in this thread. Apologies offered for any confusion caused.

 

[JMC3]

Hi all. thanks To all, especially @PADDO @uHu and @IndroCruise I have read all of the forum front to back and I think I am doing the right things, but I still have a very harsh ride - particularly in the rear. I have a quick question: should brand new fluid be foamy when bleeding the PS rear Accumulator/actuator?

details: I did another (3rd) bleed of the AHC system today because I have a harsh ride seemed to have air in the lines (a bleed on the right rear actuator/accumulator was foamy). I am confient I am doing the process correctly. One of the final steps of the bleed process is a “quick bleed” of the PS accumulators. All was perfect (clean and clear fluid). I drove the truck around for a while and ran L to H tests a couple of times. I was a little over the Max line in the reservoir, so I decided to do a quick bleed, sarting with PS rear. Fluid was very foamy from the PS rear. everyother location is fine. I thinkI am taking on air somewhere. Or is this normal?

I am close to spec on most points, although N to H and H to N are quick (<5 secs and +/-8 secs). without going to the nitty gritty details on all of the specs, should I be seeing foamy AHC fluid in the PS Rear actuator and could this be causing a harsh ride? If not, what should I be researching as a resolution?
thanks!

 

[PabloCruise]

I wonder if that globe is leaking?

 

[IndroCruise]

Hi all. thanks To all, especially @PADDO @uHu and @IndroCruise I have read all of the forum front to back and I think I am doing the right things, but I still have a very harsh ride - particularly in the rear. I have a quick question: should brand new fluid be foamy when bleeding the PS rear Accumulator/actuator?

details: I did another (3rd) bleed of the AHC system today because I have a harsh ride seemed to have air in the lines (a bleed on the right rear actuator/accumulator was foamy). I am confient I am doing the process correctly. One of the final steps of the bleed process is a “quick bleed” of the PS accumulators. All was perfect (clean and clear fluid). I drove the truck around for a while and ran L to H tests a couple of times. I was a little over the Max line in the reservoir, so I decided to do a quick bleed, sarting with PS rear. Fluid was very foamy from the PS rear. everyother location is fine. I thinkI am taking on air somewhere. Or is this normal?

I am close to spec on most points, although N to H and H to N are quick (<5 secs and +/-8 secs). without going to the nitty gritty details on all of the specs, should I be seeing foamy AHC fluid in the PS Rear actuator and could this be causing a harsh ride? If not, what should I be researching as a resolution?
thanks!

As a starting point, suggest zero in on condition of ‘globes’:

1. If not already done, check hub-to-fender operating heights with tape AND check front and rear AHC neutral pressures with Techsteam or other scanner. Adjust for correct heights and correct pressures if necessary. The purpose of this is to ensure that volume test (difference between “LO” height and “HI” height as measured by graduations at AHC Tank) is consistent with FSM and is not misleading. Record all results and measurements. Note that AHC pressures by themselves tell you nothing about ‘globe’ condition,
2. Carry out the actual volume test, observe and record difference in graduations at AHC Tank between “LO” height of vehicle and “HI” height of vehicle – purpose of this is to gain an indication of overall condition of ‘globes’ (14 = as new, 7 = replace ‘globes’, at the conditions specified in the FSM),
3. Carry out “16 step test” to see if any difference can be observed between the various corners of vehicle – purpose of this is to see if it is possible to discern any difference between ‘globes’ (although condition of Damping Force Actuators also are implicated in this test). To find details of this test, search on IH8MUD for “16 step test” by @PADDO – there are many replies by @PADDO in a number of different threads and you will soon get the idea,
4. If poor ‘globe’ condition is indicated, plan replacement of ‘globes’. It is possible (but unusual) for one ‘globe’ to fail catastrophically by itself but if one ‘globe’ is failing then it is likely that others are not far behind. Best to replace all four ‘globes’ as a set although some replace ‘globes’ in pairs, front and rear.

Note that ‘rough ride’ can have several other causes – commonly, problematic or wrongly adjusted Height Control Sensors. Sensor problems may cause the AHC Electronic Control Unit (ECU) to put the system into ‘fail safe mode’ in which variable damping rates are prohibited and ride feels rough, particularly at low speeds.

When confident of 'globe' condition, and if 'rough ride' persists, proceed to Height Control Sensors. Other different problems also are possible, although less likely, and can be considered later -- this is enough for a start.

Search in IH8MUD for "Height Control Sensors" by @uHu to find some good insights and pics on Height Control Sensor issues. A relevant FSM extract also is attached.

Late edit: By the way, the whole system is under pressure, so air cannot enter unless drawn in when the system is opened to replace parts or during the bleeding process or in other situations when the fluid level in the AHC tank has fallen too low, allowing the pump to "suck air". Bubbles can arise when the diaphragm in the 'globe' deteriorates and allows nitrogen to escape into the fluid (and fluid moves past the diaphragm into the gas side of the 'globe'). Some fine bubbles also can be expected when entrained gas in a fluid under pressure then depressurises (see Henry's Law from high school physics/chemistry). However, if you are confident that bleeding has been done well, then nitrogen from the gas side of 'globe(s)' seems more likely your situation .

 

[JMC3]

As a starting point, suggest zero in on condition of ‘globes’:

1. If not already done, check hub-to-fender operating heights with tape AND check front and rear AHC neutral pressures with Techsteam or other scanner. Adjust for correct heights and correct pressures if necessary. The purpose of this is to ensure that volume test (difference between “LO” height and “HI” height as measured by graduations at AHC Tank) is consistent with FSM and is not misleading. Record all results and measurements. Note that AHC pressures by themselves tell you nothing about ‘globe’ condition,
2. Carry out the actual volume test, observe and record difference in graduations at AHC Tank between “LO” height of vehicle and “HI” height of vehicle – purpose of this is to gain an indication of overall condition of ‘globes’ (14 = as new, 7 = replace ‘globes’, at the conditions specified in the FSM),
3. Carry out “16 step test” to see if any difference can be observed between the various corners of vehicle – purpose of this is to see if it is possible to discern any difference between ‘globes’ (although condition of Damping Force Actuators also are implicated in this test). To find details of this test, search on IH8MUD for “16 step test” by @PADDO – there are many replies by @PADDO in a number of different threads and you will soon get the idea,
4. If poor ‘globe’ condition is indicated, plan replacement of ‘globes’. It is possible (but unusual) for one ‘globe’ to fail catastrophically by itself but if one ‘globe’ is failing then it is likely that others are not far behind. Best to replace all four ‘globes’ as a set although some replace ‘globes’ in pairs, front and rear.

Note that ‘rough ride’ can have several other causes – commonly, problematic or wrongly adjusted Height Control Sensors. Sensor problems may cause the AHC Electronic Control Unit (ECU) to put the system into ‘fail safe mode’ in which variable damping rates are prohibited and ride feels rough, particularly at low speeds.

When confident of 'globe' condition, and if 'rough ride' persists, proceed to Height Control Sensors. Other different problems also are possible, although less likely, and can be considered later -- this is enough for a start.

Search in IH8MUD for "Height Control Sensors" by @uHu to find some good insights and pics on Height Control Sensor issues. A relevant FSM extract also is attached.

Late edit: By the way, the whole system is under pressure, so air cannot enter unless drawn in when the system is opened to replace parts or during the bleeding process or in other situations when the fluid level in the AHC tank has fallen too low, allowing the pump to "suck air". Bubbles can arise when the diaphragm in the 'globe' deteriorates and allows nitrogen to escape into the fluid (and fluid moves past the diaphragm into the gas side of the 'globe'). Some fine bubbles also can be expected when entrained gas in a fluid under pressure then depressurises (see Henry's Law from high school physics/chemistry). However, if you are confident that bleeding has been done well, then nitrogen from the gas side of 'globe(s)' seems more likely your situation .

Thanks a million. I appreciate the help. Makes perfect sense. I think I’ve got a bad globe on the PS Rear. But that may be the smaller problem. I think you are correct that I have sensor issues.....

 

[JMC3]

As a starting point, suggest zero in on condition of ‘globes’:

1. If not already done, check hub-to-fender operating heights with tape AND check front and rear AHC neutral pressures with Techsteam or other scanner. Adjust for correct heights and correct pressures if necessary. The purpose of this is to ensure that volume test (difference between “LO” height and “HI” height as measured by graduations at AHC Tank) is consistent with FSM and is not misleading. Record all results and measurements. Note that AHC pressures by themselves tell you nothing about ‘globe’ condition,
2. Carry out the actual volume test, observe and record difference in graduations at AHC Tank between “LO” height of vehicle and “HI” height of vehicle – purpose of this is to gain an indication of overall condition of ‘globes’ (14 = as new, 7 = replace ‘globes’, at the conditions specified in the FSM),
3. Carry out “16 step test” to see if any difference can be observed between the various corners of vehicle – purpose of this is to see if it is possible to discern any difference between ‘globes’ (although condition of Damping Force Actuators also are implicated in this test). To find details of this test, search on IH8MUD for “16 step test” by @PADDO – there are many replies by @PADDO in a number of different threads and you will soon get the idea,
4. If poor ‘globe’ condition is indicated, plan replacement of ‘globes’. It is possible (but unusual) for one ‘globe’ to fail catastrophically by itself but if one ‘globe’ is failing then it is likely that others are not far behind. Best to replace all four ‘globes’ as a set although some replace ‘globes’ in pairs, front and rear.

Note that ‘rough ride’ can have several other causes – commonly, problematic or wrongly adjusted Height Control Sensors. Sensor problems may cause the AHC Electronic Control Unit (ECU) to put the system into ‘fail safe mode’ in which variable damping rates are prohibited and ride feels rough, particularly at low speeds.

When confident of 'globe' condition, and if 'rough ride' persists, proceed to Height Control Sensors. Other different problems also are possible, although less likely, and can be considered later -- this is enough for a start.

Search in IH8MUD for "Height Control Sensors" by @uHu to find some good insights and pics on Height Control Sensor issues. A relevant FSM extract also is attached.

Late edit: By the way, the whole system is under pressure, so air cannot enter unless drawn in when the system is opened to replace parts or during the bleeding process or in other situations when the fluid level in the AHC tank has fallen too low, allowing the pump to "suck air". Bubbles can arise when the diaphragm in the 'globe' deteriorates and allows nitrogen to escape into the fluid (and fluid moves past the diaphragm into the gas side of the 'globe'). Some fine bubbles also can be expected when entrained gas in a fluid under pressure then depressurises (see Henry's Law from high school physics/chemistry). However, if you are confident that bleeding has been done well, then nitrogen from the gas side of 'globe(s)' seems more likely your situation .

OK Guys (and thanks again @IndroCruise )
I still feels like I have no suspension at all. I went through the overall AHC/Neutral Pressure process this afternoon. Here is what found out, but I didn't do any fine tuning of the neutral pressures with Torsion bars.

1. Heights are close
-FL 19 7/8
-FR 19 3/4
-LR 20.5
-RR 20.5

Neutral to Low - 12 seconds
Low to Neutral - 17 seconds
Graduations L -> H are 10+ (even with what I believe to be a globe leaking nitro)

The height sensor readings appear to me to problematic, but I don't now how to interpret it. According to Techstream there are no error codes. how do I get negative readings on all sensors? I thought the FL and FR should balance at zero. I had all new links/bushings/stops, etc installed in the front and I recently had new OEM springs installed in the rear. Perhaps the local dude that did the installations for me tweaked the sensors or linkage somehow. not sure if a tweaked sensor would cause these readings or the rough ride.

I plan to do the 1-16 actuator test tomorrow, but any help identifying where I should be investigating is much appreciated. I don’t think the slightly high rear neutral pressures are my problem. Thanks!!

 

[IndroCruise]

OK Guys (and thanks again @IndroCruise )
I still feels like I have no suspension at all. I went through the overall AHC/Neutral Pressure process this afternoon. Here is what found out, but I didn't do any fine tuning of the neutral pressures with Torsion bars.

1. Heights are close
-FL 19 7/8
-FR 19 3/4
-LR 20.5
-RR 20.5

Neutral to Low - 12 seconds
Low to Neutral - 17 seconds
Graduations L -> H are 10+ (even with what I believe to be a globe leaking nitro)

The height sensor readings appear to me to problematic, but I don't now how to interpret it. According to Techstream there are no error codes. how do I get negative readings on all sensors? I thought the FL and FR should balance at zero. I had all new links/bushings/stops, etc installed in the front and I recently had new OEM springs installed in the rear. Perhaps the local dude that did the installations for me tweaked the sensors or linkage somehow. not sure if a tweaked sensor would cause these readings or the rough ride.

I plan to do the 1-16 actuator test tomorrow, but any help identifying where I should be investigating is much appreciated. I don’t think the slightly high rear neutral pressures are my problem. Thanks!!

View attachment 2472354

View attachment 2472355

Deepest sympathy for these frustrations!! My vehicle has some unresolved problems with some similarities and some differences to your case. I will write up my situation in the next few days and post a separate story, so as not to distract others from replying to your own post above.

Meanwhile, here are a few thoughts on your readout:

At first blush, the basic readings appear ‘healthy’: presume ‘cross-levelling’ is OK, correct-looking physically measured hub-to-fender operating heights, not unusual AHC pressures, and the HI/LO 10+ graduations look good!

However …….

The top three lines showing Height Sensor positions at the end of the LO to N movement are strange. The differences between each Sensor are not huge but it is unusual that they are ALL not closer to zero and are significantly below zero. This is a particular concern if this is observed consistently with repeated measurements when moving from LO to N.

It does raise questions as to whether the lift from LO to N actually has been completed by the system, and if not, what is preventing the system from doing so?

The design is such the system is meant to find the ‘null’ point at which the Height Control Sensors give a close-to-zero reading when the vehicle has raised to N -- for any N height chosen by the person who last manually adjusted the Height Control Sensor positions at N.

Different effects can be tricky to diagnose, because some obscure faults may not result in in a Diagnostic Trouble Code (DTC). These could include situations such as mechanical issues in the suspension, or, weaknesses such as a continuing but not yet fatal decline in AHC pump performance, or, a developing blockage impeding pressure build-up and flow of AHC fluid at the pump or elsewhere, or, improper operation of the solenoid valve on the large Height Control Accumulator, or, faulty valve operation in the Control Valve Assembly, etc.

Note that there is no ‘brain-power’ or control loop inside in the Height Control Sensors. They are mere sensors -- simple but robust potentiometers in which a different vehicle height causes the tiny internal brushes to be at a different position on a carbon trace, in turn giving a different resistance and different output voltage, interpreted as a relative height by the AHC Electronic Control Unit.

Only physical adjustment of this Sensor position is possible, and this must result in a matching actual change in the hub-to-fender measurement. I am unaware of any way that the Sensor readings can be “zero’d” or adjusted in Techstream. Other IH8MUD Members may know different.

It would be tricky. This is because heights and pressures are interdependent. Or more precisely, the torsion bar deflection depends on the load carried (like a spring) and load not carried by the torsion bar must be carried by the relevant AHC Actuator and Gas Chamber (‘globe’).

The only means of load transfer between torsion bar and AHC is via manual adjustment of the torsion bar adjuster. The AHC Electronic Control Unit has no connection with the torsion bars nor control over them. The ECU can read the AHC Pressure signal and the Height Control Sensor signal and respond to those (among the multiple other signals it receives).

The ECU cannot itself optimise torsion bar load, AHC load and vehicle height a.k.a. hub-to-fender measurements.

So questions arise from your readings:

What are the hub-to-fender measurements immediately after the N >> LO >> N height movements and AHC pressure readings?

Are the hub-to-fender measurements at this point the same as those given in the above post, or, are they now lower, giving rise to the lower sensor readings?

If lower, then the AHC pressures relate to those lower measurements and the AHC pressures would be higher at the higher measurements (and ride comfort would be different, and likely rougher).

Do the hub-to-fender measurements change after you have driven around the block and the suspension has settled?

If so, how can the AHC pressures be determined at these higher hub-to-fender measurements?

At the moment, I cannot offer a clever answer to these questions but only report that currently I am dealing with a very similar problem on my own vehicle …..

Meanwhile, I have pasted a couple of links below which highlight some different problems and ideas – they may or may not be relevant and you may have seen them previously.

I also notice that your steering angle seems quite a long way from zero. It is unlikely ever to be perfect but if this is the repeatable reading with the front wheels truly straight ahead, then it suggests that toe-in or some other aspect of wheel alignment may have been achieved in unequal ways on Right and Left wheel alignment adjusters, or that there is something worn or incorrect in the suspension or steering mechanicals, or that there is something wrong with the Steering Angle Sensor.

The relevance is that when the ECU thinks that the wheels are straight ahead, the ECU directs the front gate valves in the Gate Valve Assembly to be open, which causes Right and Left front AHC pressures to be equalised.

When the angle exceeds 36 degrees (check FSM), the relevant gate valve closes and Left and Right pressures cannot equalise. This is how some variable roll resistance is included in the AHC/TEMS system in addition to the mechanical sway bars.

So I am wondering whether your -51.75 degrees steering angle at ‘straight ahead’ actually means that there is some pressure "locked in" by the gate valve affecting one side and distorting your efforts to ‘cross level’ correctly and preventing equalised front torsion bar loadings?

Hopefully, other IH8MUD Members will have more to offer on all of the above matters?

Several easy and practical indicators which I use are suggested below:

These suggestions may give you further information about how the system is operating, or, whether it is not operating due to a fault condition or ‘fail safe mode’ in the AHC/TEMS systems, or, whether suspension/steering mechanical issues should be explored:

• The Height Control obviously works because you can lower and raise the vehicle, take pressure readings and do the HI/LO volume test. So that much is a positive. It leaves us wondering about the adaptive variable suspension component of TEMS,

• Suggest drive over a set course a few times, preferably with little traffic, so that you can concentrate on the vehicle, then on each go-round use a different setting on the four-position Comfort Switch on the console, then sense by the seat-of-the-pants whether there are differing degrees of ‘felt comfort’ at each setting. It seems that you already have done this and the harsh ride is one 'symptom' you have experienced. Is the experience the same at all Comfort Switch settings?

• Suggest hook-up Techstream so that you can safely look at the screen while driving, or better still, have someone else drive while you look at Techstream screen,

• On the screen, you should be able to see all of the Height Sensors responding in almost real time to the ground over which you are passing. If any of them are not moving or seem to be moving erratically and inconsistently with ground conditions, then that is a worry and warrants a closer look at the relevant Sensor(s),

• Now suggest look at the following lines on the Techstream readout on the screen of your laptop or device while the vehicle is still on the move:

• “Front Wheel Step” and “Rear Wheel Step”: These should indicate whether the ECU is signalling the step motors in the Damping Force Actuators to operate in the appropriate range for the chosen setting on Comfort Switch on the console. When the vehicle is stationary, both Front and Rear readings should show position 8 (of 16 positions). In at least one of the ‘fail safe modes’ the system may remain in this position 8 even when the vehicle moves. If so, that is a 'symptom' worth knowing. Suggest take some screenshots to look at later,

• Suggest vary the Comfort Switch through each of the four positions while the vehicle is moving and study the responses. If the system is working, at ‘Comfort’ (softest damping) you should see a wide range, say 1 to 9, at ‘Normal’ it is more like 3 to 12, at Sport1 maybe 8 to 12, at Sport2 (hardest damping) maybe 12 to 14. (These are approximate numbers from my memory only). In most Comfort Switch positions, large changes in damping also may be seen during hard turns, or heavy stops, or heavy accelerations. This gives some evidence of what the system is doing or not doing. Again, suggest take some screenshots to look at later,

• While making the observations in the above para, also while still on the move, look at the lines “Damping Force Switch 1” and “Damping Switch 2”. These refer to the instructions given to “Soft Damping Force Valve” and the “Hard Damping Force Valve” found inside each Damping Force Control Actuator. This is about HOW the ECU controls the ‘damping map’ to be used according to the choice of Comfort Switch position on the console. As I understand it, these lines in the readout indicate the signal sent by the ECU to the Actuators rather than what the Actuator actually does! A discrepancy between the ECU and the Actuator should result in a DTC,

• As you move the Comfort Switch on the console through its four positions, you should see the four different combinations of switching for each of Switch positions, ending with both switches OFF at the Sport2, the hardest setting. I have not tried it but I also surmise that the switching may change in a hard turn, driven by the Steering Angle Sensor? Again, suggest collect data with screenshots. (Note that there is no ‘brain power’ in the Damping Force Control Actuators – the instructions come from the ECU and control movements of the step motors and solenoid operation of the internal valves),

• It is worth revisiting the “Damping Force Controlling Condition Check” (also known as the ‘16 Step Test’) , and, “Height Control Operation Test” (also known as the ‘Active Test’) to test properly the functionality of these parts of the AHC/TEMS system, before moving on to other issues.

• The FSM reference is: https://lc100e.github.io/manual/,
• Follow index tabs to Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS > PRE-CHECK,
• Then go to Item 4 on page DI-213 and Item 5 on page DI-214.
• Note that bridging terminals E1 to Ts at DLC1 in the engine bay with an unbent paperclip is the same as, but much more comfortable than dealing with the connections at DLC3 mentioned in these FSM references, while upside down under the dashboard!
• Make the connections with the engine and ignition OFF, then start the engine. Remember to turn OFF the engine and then remove the bridge when finished.
• See also this succinct summary from @PADDO: AHC with harsh ride .
• As @PADDO mentions, the vehicle can be driven in this condition and the Techstream screen readouts and vehicle response can be observed on the road at each of the 16 actuator switch settings one-by-one – but CAREFULLY because in this condition the adaptive variable suspension, ABS and A-TRC are all OFF with multiple dashboard warning lights flashing. These systems will automatically restore when the engine/ignition is switched OFF, bridge removed and the engine re-started.

• Finally, here is a quick on-vehicle Height Control Sensor test provided by @uHu: 2007 LC “VX” -- first reply by @uHu, and, 2007 LC “VX” -- second reply by @uHu ,
• By the way, it is not a hard job to remove the Sensors from the vehicle – two accessible bolts to the chassis, one linkage bolt to a sliding adjuster, a couple of cable clips, and one fiddly electrical connector to unlock and release in each case.
• Make access easy at the front by raising to HI height and turning the front wheel to full lock,
• At the rear, either remove LHS rear wheel or get under the car,
• NEVER get under the vehicle when dealing with any part of the AHC system without putting car stands in place under the chassis rails to ensure that the car is positively and physically prevented from lowering itself onto a person -- it can happen, has happened but it should never be allowed to happen!

Strong recommendation: Take photos before removal of the Height Control Sensors so that you have clear record of your starting point. Once removed, inspecting sensor internals and testing is very straightforward and makes any replacement decision easy. Take more photographs. Record measurements for later reference. Along the way, also test the harness circuit for supply voltage and continuity.
Two posts with more explanation – with pictures
AHC, Actual Height, Pressures - LC100

This next post includes comments and attachments on more diagnostic approaches and material:
2007 LC “VX” -- see notes in reply by @IndroCruise.

Last reference: Probably this document has been seen previously but is recommended that it be printed in hardcopy and re-read every time when dealing with AHC/TEMS problems. It provides a good well-illustrated 20-page descriptive reminder of how all the parts of this 25-year old, robust-if-well-cared-for technology can still work together to produce a great ride:
The FSM reference is: https://lc100e.github.io/manual/,
Follow index tabs from the top to
New Car Features > CHASSIS > Suspension > Active Height Control & Skyhook TEMS

More later after I do some more work on my vehicle!

 

[JMC3]

Thanks a million. I appreciate the help. Makes perfect sense. I think I’ve got a bad globe on the PS Rear. But that may be the smaller problem. I think you are correct that I have sensor issues.....

I am providing a quick update with a follow up question. I hope I am not driving you all crazy with this. I am grateful to this forum and all participants.

I replaced all 4 accumulator globes. Did a full @PADDO flush/bleed and did a full rundown for Neutral Pressure test. Cross level is good. All heights in spec and the foamy bleed on the RR has been eliminated. The the ride quality is WAY better! Like the truck i remember and love. But.... still throwing curious height sensor readings. See below. The damping switch is working properly. Truck raised and lowers fine. Is this something I should worry about? I am a bit of a perfectionist and want to dive in, but want to be sure this is something to be pursued. I am admittedly not much of a mechanic. Could replacing (or fixing) the height sensors make a difference in ride quality? If you all recommend I pull the height sensors, which height sensor should I start with? Seems weird all 3 be low? Something else? Thanks!

 

[PabloCruise]

The last few posts are lengthy - longer than I have time for this morning.

Once your heights and cross levels and pressures are proper, did you adjust the height sensors to 0 at N?

 

[JMC3]

The last few posts are lengthy - longer than I have time for this morning.

Once your heights and cross levels and pressures are proper, did you adjust the height sensors to 0 at N?

I didn’t. Am I supposed to manually adjust them to zero? I did a multimeter check on the front sensors and everything seems ok. I don’t remember reading from @PADDO, @uHu, @IndroCruise, @PabloCruise or the rest of you gurus that I should manually adjust the height sensors to zero once everything is in spec. Is that the prescribed action? That makes things easy if that is what I am supposed to do.