The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (5 Viewers)

[TreatSmash]

I suppose taking to Dealership is and option.

But if you want to give another shot, at removing the stuck globe today.
Harbor Freight has a forged open end wrench set. I use the 36mm form the kit. It's a very tight fit, so I tap wrench onto the globes nut for a very secure fit. Than for added leverage, I use a pipe on 36mm wrench handle. If only corners of globes nut round, you may still get a good hold on flats.

If nut now to round, which I've not seen happen (knock on wood).

My next move(s), May be:

• A cold chisel. With great care in placement, so not to damage anything other than globe.
• A chain wrench. Which could prove to difficult to get on and hold globe.
• Drill and run a steel rod though as a handle.
• If all other attempts fail. I'd remove the actuator and take to the bench.

forged 36mm. Forged is key, as they'll not flex or expand.
View attachment 3276712

I was using the harbor freight wrench set, by the time I was done I could fit the 34mm wrench on it.

Eventually I was hammering on the wrench, then using a pipe for leverage.

I had it soaked in blaster for 2 days.

I tried to remove the whole assembly, I removed 2 bolts holding it to the frame plus 2 fluid lines and it wouldn't budge. I could not figure out what else was holding it in place. I had just spend the last 6 hours breaking a globe, I didn't want to push my luck and break more.

I don't have a chain wrench, nor does HF but that's what Lexus said they will probably use.

 

[IndroCruise]

We'll see, I could only get 3/4 globes off and totally wrecked the 4th one trying so I have to take it to the dealership (Lexus they have a good AHC guy here) on Monday.



That being said I still went from 7 to15 graduations with just 3 globes.



I didn't expect it to effect the rake or the height of the ride, but since I am replacing the globes and flushing I was planning on going ahead and cross leveling and adjusting the sensors as needed as well.



I'm not really too worried about anything until I get that 4th globe in.

I already had 19.5" for my front measurements, so I went ahead and tried the Active Test. The car height did not change when I used the AHC up and down buttons. I did hear a noise from the front driver side when I pressed the up button, but I couldn't tell if it was the accumulator or globe. Here is a video:



Also of note, when I observed the AHC fluid reservoir, it was at the correct level at N, but it seemed that the fluid was a bit bubbly, that there was a bubbly SQUIRT sound from the tank at the very end of the adjustment, and the sound of the pump ended up with a slight high-pitched noise which I imagine is what it sounds like when people on here have talked about 'cavitation' sounds from the AHC pump.

Although clearly something is wrong, I do not have any DTCs, and the car is still making full L/N/H height adjustments, as well as a definite difference in softness/pushness/bounciness of the ride going from Sport -> Comfort+. Previously I had flushed the AHC fluid and the fluid from the accumulator had been a bit bubbly, but at the end of the bleed I was getting fresh fluid from all 5 bleed points (and 10+ gradations on the test, although I know now that testing that is premature). After the flush there was also a definite difference in the car being less rigid.

Anyways, after failing the Active Test, I went ahead and tried zeroing out the sensor heights anyway, and ran into another problem: rear sensor height is in the negative despite lowering adjustment all the way to the bottom of the slider.

I then drove around the block and when I parked again, the sensor heights had changed, and now the truck was sitting lower: 19.25 in the front, 19.75 in the back (see first image below).

Then I still went ahead and tried cycling through the height control just to see what pressures I would get, and those are below. (Goes N > L > N > H > N):

N
View attachment 3275979
L
View attachment 3275978
N
View attachment 3275981
H
View attachment 3275977
N
View attachment 3275982

What next?

“I already had 19.5" for my front measurements”

If this means that LH Front and RH Front are equal with engine “OFF” (no possible interference from AHC system), on a level surface such as a garage floor (not in the street -- well-engineered streets are graded and crowned to allow for rainwater drainage and are not level for this purpose), then that satisfies the first step of Front cross-levelling. (To re-iterate again, if cross-levelling is not done correctly on a suitable level surface, then the Front hub-to-fender measurements and the Front Height Control Sensor readings all contain an error which will confound all further work).

Let’s assume (i) that cross-levelling has been done correctly and that the LH Front and RH Front are equal on a level surface, and, (ii) the Front ‘ride height’ conveniently turns out to be 19.5 inches on both sides.

Some mentors such as @PADDO suggest 19.75 inches is the aim, more recent input from @2001LC suggests 19.50 inches is a better target for which he gives good reasons. Suggest leave the Front of your vehicle as it is, no further adjustment necessary, and far and away the most important thing is that LH Front and RH Front hub-to-fender heights are equal on a genuinely level surface at whatever heights you choose.

If so, all is good, start from there.

Now turn to Techstream read-outs after N > LO > N moves in your Post #362 and in your Post #378 -- the first point being that the AHC pressure readings -- Front, Rear and Height Control Accumulator -- all derive in a sequence from the single pressure sensor located next to the AHC Pump (with the Height Control Accumulator being re-charged and showing its pressure reading some time after the green AHC indicator light stops flashing). It is worth allowing up to 30 seconds for the Height Control Accumulator to re-charge after the green light stops flashing. The AHC Pump can be heard to stop when the re-charge is done.

The AHC pressure readings at N and HI are not reliable for any useful purpose -- because of the way the readings are overwritten and held in the ECU memory.

The pressure readings after the N > LO > N height movements are the only useful pressure data for diagnostic purposes and for comparison purposes with the FSM-specified pressures. All AHC adjustments are done only at N height.

If I have understood correctly which Techstream screenshots across your various Posts corresponds to N > LO > N movements, then the conclusion is that the Front and Rear AHC Pressures are considerably higher than the FSM-specified AHC Pressures, not out-of-this-world high, but high enough to require correction for optimum damping and ride comfort and for system longevity, and avoidance of leakage risks at ‘shock absorbers’ and elsewhere. These will need correction in due course -- and when the pressures are corrected, it would be appropriate to test the overall condition of ‘globes’ by observing the change in graduations from “HI” to “LO”, then record the details and the pressures as a base-line for future reference.

Moving to the Height Control Sensor readings ….

Unlike the pressure readings, the readings of healthy Height Control Sensors seen on Techstream are reliable in real time, changes are almost instantaneous, and reflect the position of the Height Control Sensor at any time, regardless of the sequence of height movements in the test process. This is kind of obvious because the Height Control Sensor sends signals to the Suspension ECU continuously in real time as the vehicle travels -- which enables the Active Height Control (AHC) to work as intended.

Per FSM, the Height Control Sensor readings with the vehicle at rest N are meant to be close to zero +/- 5 millimetres or +/- 0.2 inches AND the three Sensors should not be much different from each other.

Signals from the Height Control Sensor to the Suspension ECU actually are in voltages. For operational purposes, the ECU and/or Techstream translates these voltage signals to millimetres or inches according to whether Metric or US units were chosen somewhere in Techstream settings. We won’t get into a digression about this here -- except to say that the voltage changes are proportional to the height changes.

So inspect all of your Techstream screenshots at N height, noting the following:

1. There are no DTC’s -- but there are limitations to the meaning of the Height Control Sensor circuit DTC’s as discussed back at Post #368 this thread – and Height Control Sensor circuit health cannot be assumed by the absence of a DTC,

2. You have ensured that the vehicle level across the Front on a level surface.

3. Your Techstream Height Control Sensor readings at N are trying to tell you that LHS Front and RHS Front are not level – LHS Front is lower than RHS Front by about 5 millimetres– but you know that this physically is not true! The Rear Height Control Sensor says that it is lower than RHS Front by about 10 millimetres – but unless you can physically see that the vehicle is raked lower to the Rear (highly unusual), then that is not true either!

4. Even though the vehicle is relatively young (2006 LX470?), these differences in readings at N mean that the three Height Control Sensor circuits are suspicious (meaning Sensor plus Connector plus harness all the way back to the ECU, including the now-infamous BI1 connector block high up in the LHS rear quarter panel).

5. The Techstream Height Control Sensor readings at N also are all negative -- trying to tell you that the raise is not complete and the vehicle is low, that the raise has stopped before the vehicle arrived at the heights necessary for the FSM-specified height sensor readings to appear on Techstream – meaning, close to zero +/- 5 millimetres or +/- 0.2 inches. This further increases suspicions about the Height Control Sensor circuits,

6. You know that the vehicle is at the tape-measured physical hub-to-fender heights you require on a level surface – although the Rear Hub-to-Fender heights have not been quoted,

7. You know that the differences in the Height Control Sensor readings, while not good, are not large enough to cause the ECU to initiate the ‘fail safe function’ -- because the AHC and TEMS systems have not been prohibited and are still working.

8. The recorded noise on Youtube does not sound like AHC Pump operation re-charging the Height Control Accumulator – the noise is very hard to distinguish from normal engine and fan noise. It is possible (but unusual) that the Height Control Accumulator solenoid is not opening and closing correctly. When healthy and re-charged, the Height Control Accumulator should enable a quick raise from LO to N -- but there will be interference if there are faults in the Height Control Sensor circuits because, given the differences, the ECU may be slow or unable to resolve the correct position at N height. Suggest time the raise from LO > N and N > HI and compare with FSM,

9. The reported ‘squirty’ effect and brief high pitch noise at the end of a raise -- actually at the end of the Height Control Accumulator re-charge -- does not seem particularly unusual. At this point, and at the high final charging pressure of about 10.5 Mpa (about 1,500 psi), the Height Control Accumulator solenoid closes and the AHC Pump stops. There will be a bump,

10. The Height Control Operation Test, alias “Active Test” procedure apparently does not drive height functions as it should, using this sequence –

(a) bridge terminals Ts and E1 at DLC1

(b) Initiate test function by pushing the DOWN button of the height selection switch 5 times or more within 5 seconds of starting the engine

(c) Select COMFORT mode

(d) Test Front by pushing UP and DOWN Buttons

(e) Test Rear by push and hold height control ON/OFF switch AND simultaneously pushing UP and DOWN buttons.

11. It is important to double-check this “Active Test” procedure.

12. The reported non-operation of “Active Test” is unusual when the vehicle moves LO > N > HI > N > LO in normal AHC height control operation and noting that TEMS damping is operating normally as well.

13. It is highly significant that height functions will not operate under Height Control Operation Test, alias “Active Test”, but the AHC function does operate normally. If that truly is the case, then coupled with the above observations and also the observation that the vehicle comes to different heights after a ‘drive around the block’, this all adds even more to suspicions about the Height Control Sensor circuits.

So what next?

Suggest in this order ....

A. Replace the Rear Height Control Sensor – the behaviour of this circuit is highly suspicious,

B. Remove and test both Front Height Control Sensors per FSM, re-install and adjust -- if these Sensors do not respond to cleaning and adjustment, replace (or for peace of mind replace anyway),

C. Use a multimeter and FSM Electrical Wiring Diagrams (EWD’s) to explore harness faults – including all the way back to the now-infamous BI1 connector block high up in the LHS rear quarter panel as highlighted by @suprarx7nut and @2001LC, as discussed in post #9 and other posts in this thread:
AHC done? - https://forum.ih8mud.com/threads/ahc-done.1299423/#post-14719487

 

[2001LC]

I was using the harbor freight wrench set, by the time I was done I could fit the 34mm wrench on it.

Eventually I was hammering on the wrench, then using a pipe for leverage.

I had it soaked in blaster for 2 days.

I tried to remove the whole assembly, I removed 2 bolts holding it to the frame plus 2 fluid lines and it wouldn't budge. I could not figure out what else was holding it in place. I had just spend the last 6 hours breaking a globe, I didn't want to push my luck and break more.

I don't have a chain wrench, nor does HF but that's what Lexus said they will probably use.

WOW, must be rusted to the frame!

 

[usedname]

“I already had 19.5" for my front measurements”

If this means that LH Front and RH Front are equal with engine “OFF” (no possible interference from AHC system), on a level surface such as a garage floor (not in the street -- well-engineered streets are graded and crowned to allow for rainwater drainage and are not level for this purpose), then that satisfies the first step of Front cross-levelling. (To re-iterate again, if cross-levelling is not done correctly on a suitable level surface, then the Front hub-to-fender measurements and the Front Height Control Sensor readings all contain an error which will confound all further work).

Let’s assume (i) that cross-levelling has been done correctly and that the LH Front and RH Front are equal on a level surface, and, (ii) the Front ‘ride height’ conveniently turns out to be 19.5 inches on both sides.

Some mentors such as @PADDO suggest 19.75 inches is the aim, more recent input from @2001LC suggests 19.50 inches is a better target for which he gives good reasons. Suggest leave the Front of your vehicle as it is, no further adjustment necessary, and far and away the most important thing is that LH Front and RH Front hub-to-fender heights are equal on a genuinely level surface at whatever heights you choose.

If so, all is good, start from there.

Now turn to Techstream read-outs after N > LO > N moves in your Post #362 and in your Post #378 -- the first point being that the AHC pressure readings -- Front, Rear and Height Control Accumulator -- all derive in a sequence from the single pressure sensor located next to the AHC Pump (with the Height Control Accumulator being re-charged and showing its pressure reading some time after the green AHC indicator light stops flashing). It is worth allowing up to 30 seconds for the Height Control Accumulator to re-charge after the green light stops flashing. The AHC Pump can be heard to stop when the re-charge is done.

The AHC pressure readings at N and HI are not reliable for any useful purpose -- because of the way the readings are overwritten and held in the ECU memory.

The pressure readings after the N > LO > N height movements are the only useful pressure data for diagnostic purposes and for comparison purposes with the FSM-specified pressures. All AHC adjustments are done only at N height.

If I have understood correctly which Techstream screenshots across your various Posts corresponds to N > LO > N movements, then the conclusion is that the Front and Rear AHC Pressures are considerably higher than the FSM-specified AHC Pressures, not out-of-this-world high, but high enough to require correction for optimum damping and ride comfort and for system longevity, and avoidance of leakage risks at ‘shock absorbers’ and elsewhere. These will need correction in due course -- and when the pressures are corrected, it would be appropriate to test the overall condition of ‘globes’ by observing the change in graduations from “HI” to “LO”, then record the details and the pressures as a base-line for future reference.

Moving to the Height Control Sensor readings ….

Unlike the pressure readings, the readings of healthy Height Control Sensors seen on Techstream are reliable in real time, changes are almost instantaneous, and reflect the position of the Height Control Sensor at any time, regardless of the sequence of height movements in the test process. This is kind of obvious because the Height Control Sensor sends signals to the Suspension ECU continuously in real time as the vehicle travels -- which enables the Active Height Control (AHC) to work as intended.

Per FSM, the Height Control Sensor readings with the vehicle at rest N are meant to be close to zero +/- 5 millimetres or +/- 0.2 inches AND the three Sensors should not be much different from each other.

Signals from the Height Control Sensor to the Suspension ECU actually are in voltages. For operational purposes, the ECU and/or Techstream translates these voltage signals to millimetres or inches according to whether Metric or US units were chosen somewhere in Techstream settings. We won’t get into a digression about this here -- except to say that the voltage changes are proportional to the height changes.

So inspect all of your Techstream screenshots at N height, noting the following:

1. There are no DTC’s -- but there are limitations to the meaning of the Height Control Sensor circuit DTC’s as discussed back at Post #368 this thread – and Height Control Sensor circuit health cannot be assumed by the absence of a DTC,

2. You have ensured that the vehicle level across the Front on a level surface.

3. Your Techstream Height Control Sensor readings at N are trying to tell you that LHS Front and RHS Front are not level – LHS Front is lower than RHS Front by about 5 millimetres– but you know that this physically is not true! The Rear Height Control Sensor says that it is lower than RHS Front by about 10 millimetres – but unless you can physically see that the vehicle is raked lower to the Rear (highly unusual), then that is not true either!

4. Even though the vehicle is young, these differences in readings at N mean that the three Height Control Sensor circuits are suspicious (meaning Sensor plus Connector plus harness all the way back to the ECU, including the now-infamous BI1 connector block high up in the LHS rear quarter panel0.

5. The Techstream Height Control Sensor readings at N also are all negative -- trying to tell you that the raise is not complete and the vehicle is low, that the raise has stopped before the vehicle arrived at the heights necessary for the FSM-specified height sensor readings to appear on Techstream – meaning, close to zero +/- 5 millimetres or +/- 0.2 inches. This further increases suspicions about the Height Control Sensor circuits,

6. You know that the vehicle is at the tape-measured physical hub-to-fender heights you require on a level surface – although the Rear Hub-to-Fender heights have not been quoted,

7. You know that the differences in the Height Control Sensor readings, while not good, are not large enough to cause the ECU to initiate the ‘fail safe function’ -- because the AHC and TEMS systems have not been prohibited and are still working.

8. The recorded noise on Youtube does not sound like AHC Pump operation re-charging the Height Control Accumulator – the noise is very hard to distinguish from normal engine and fan noise. It is possible (but unusual) that the Height Control Accumulator solenoid is not opening and closing correctly. When healthy and re-charged, the Height Control Accumulator should enable a quick raise from LO to N -- but there will be interfence if there are faults in the Height Control Sensor circuits because, given the differences, the ECU may be slow or unable to resolve the correct position at N height. Suggest time the raise from LO > N and N > HI and compare with FSM,

9. The reported ‘squirty’ effect and brief high pitch noise at the end of a raise -- actually at the end of the Height Control Accumulator re-charge -- does not seem particularly unusual. At this point, and at an high charging pressure of about 10.5 Mpa, the Height Control Accumulator solenoid closes and the AHC Pump stops. There will be a bump,

10. The Height Control Operation Test, alias “Active Test” procedure apparently does not drive height functions as it should, using this sequence –

(a) bridge terminals Ts and E1 at DLC1

(b) Initiate test function by pushing the DOWN button of the height selection switch 5 times or more within 5 seconds of starting the engine

(c) Select COMFORT mode

(d) Test Front by pushing UP and DOWN Buttons

(e) Test Rear by push and hold height control ON/OFF switch AND simultaneously pushing UP and DOWN buttons.

11. It is important to double-check this “Active Test” procedure.

12. The reported non-operation of “Active Test” is unusual when the vehicle moves LO > N > HI > N > LO in normal AHC height control operation and noting that TEMS damping is operating normally as well.

13. It is highly significant that height functions will not operate under Height Control Operation Test, alias “Active Test”, but the AHC function does operate normally. If that truly is the case, then coupled with the above observations and also the observation that the vehicle comes to different heights after a ‘drive around the block’, this all adds even more to suspicions about the Height Control Sensor circuits.

So what next?

Suggest in this order ....

A. Replace the Rear Height Control Sensor – the behaviour of this circuit is highly suspicious,

B. Remove and test both Front Height Control Sensors per FSM, re-install and adjust -- if these Sensors do not respond to cleaning and adjustment, replace (or for peace of mind replace anyway),

C. Use a multimeter and FSM Electrical Wiring Diagrams (EWD’s) to explore harness faults – including all the way back to the now-infamous BI1 connector block high up in the LHS rear quarter panel as highlighted by @suprarx7nut and @2001LC, as discussed in post #9 and other posts in this thread:
AHC done? - https://forum.ih8mud.com/threads/ahc-done.1299423/#post-14719487

Thank you for providing your invaluable diagnostic skills!


-I am certain I have performed the Active Test correctly.

-Reassuring to hear that the pump mechanism noises are probably normal.


Unfortunately now my front ride height is 19.25 (and rears 19.75), since it seems that zeroing the sensor height leads to further 'misreads' and further AHC corrections, with sensors reading into the negatives after each zeroing. I suppose I could temporarily adjust the sensor heights to some arbitrarily positive number, perhaps +10mm. I anticipate this would raise the front height a bit. I am not certain that my fronts are not around 5mm off from each other -- I had been ignoring differences of up to 1/8" and there's easily that amount of room for error in the act of measurement.


I will return with:
1. Repeat front fender measurements (and attempt at more precise crossleveling)
2. L>N and N>H timings
3. Experiment with raising front height using sensor adjustment, and repeat N>L>N pressures


Q1: Would you recommend testing the rear height sensor in the same way as the front sensors? Are they substantially the same mechanism? -- In other words, is it a foregone conclusion that the sensor itself is bad? Just wondering before I spend $230 for a new OEM sensor off ebay.

Q2: When I remove all the sensors to test them, can I still drive the car (to move it around my driveway)?

 

[TreatSmash]

WOW, must be rusted to the frame!

It's strange because I actually have very little rust. None in that spot, who knows man.

 

[TreatSmash]

WOW, must be rusted to the frame!

Well the dealership was a terrible idea. They can get the globe off, but they wanted to charge me 3 hours labor @ $172 an hour to bleed the system.

Additionally they won't just take the globe off for liability reasons which makes sense.

So I'm back to square 1. The good news is the system is working great and I'm getting 15-16 graduations with only 3 new globes.

I just need to figure out how to get the globe off. I'm going to go buy a chain wrench.

 

[2001LC]

Well the dealership was a terrible idea. They can get the globe off, but they wanted to charge me 3 hours labor @ $172 an hour to bleed the system.

Additionally they won't just take the globe off for liability reasons which makes sense.

So I'm back to square 1. The good news is the system is working great and I'm getting 15-16 graduations with only 3 new globes.

I just need to figure out how to get the globe off. I'm going to go buy a chain wrench.

3hr to R&R 1 damage (nut) globe, plus flush! Not bad. If the nut of globe unusable.
Chain wrench likely to difficult to get on and stay on..

I do not see "why" if not rusted, you're having these issues. Other than not getting wrench on fully and squarely. These globes just aren't that tough.
I'd go at it again with 36mm wrench, with very good lighting. It's very import to clearly see whats being worked on. I'd try to get wrench on at different points, if need be.

Also, no rust and globe actuator stuck to frame, makes no sense. Unless all fasteners (IIRC: two bolt and one nut) not removed. Which also will require R&R of flare nuts. Damage those and you'll be very unhappy. Same goes for wire housing block.

 

[TreatSmash]

3hr to R&R 1 damage (nut) globe, plus flush! Not bad. If the nut of globe unusable.
Chain wrench likely to difficult to get on and stay on..

I do not see "why" if not rusted, you're having these issues. Other than not getting wrench on fully and squarely. These globes just aren't that tough.
I'd go at it again with 36mm wrench, with very good lighting. It's very import to clearly see whats being worked on. I'd try to get wrench on at different points, if need be.

Also, no rust and globe actuator stuck to frame, makes no sense. Unless all fasteners (IIRC: two bolt and one nut) not removed. Which also will require R&R of flare nuts. Damage those and you'll be very unhappy. Same goes for wire housing block.

Well I thought it was ridiculous, but what do I know. The tech made it sound like he would have the globe off in a nick and the 3 hours was to bleed the system. Considering I did 3 globes and bled the system 2x in 90 minutes on Saturday I was a bit surprised. I mean $600 is a lot of money.

The tech at Lexus said he was going to use a Chain wrench, so that's where I am going to try first.

2 bolts and 1 nut? Well I took off 1 bolt and 1 nut so maybe that's my problem

I'll report back and show you a pic of what I'm working with as a case of what not to do.

What's R&R?

 

[usedname]

I will return with:
1. Repeat front fender measurements (and attempt at more precise crossleveling)
2. L>N and N>H timings
3. Experiment with raising front height using sensor adjustment, and repeat N>L>N pressures

Alright, I am back with some measurements.

First of all, I rechecked the sensor heights today and found:
FR/FL/R
-7.6/-8.0/-13.2
Then I adjusted them to the following:
-12.6/-12.4/-13.2
When I then went from N>L>N, the measurements became:
-9.0/-7.8/-13.2
I then again adjusted the fronts to something close to the rear:
-13.6/-13.2/-13.4
After another N>L>N cycle, I obtained similar results:
-9.2/-7.8/-13.2


These are the pressures (also consistent after each N>L>N cycle):

And these are the current fender measurements - the sides are within 1/8" of each other:
FL 19 5/8
FR 19 9/16
RL 20 1/2
RR 20 3/8


And I am consistently getting the following raise times:
L>N = 19s, with a total of 38s of 'pump noise'
N>H = 7s, with total of 16s of 'pump noise'


I measured the fender heights at H as well, just to see how much height increase I'm getting and if it stays level, and again they are within 1/8":
FL 21 1/8
FR 21 3/16
RL 22 7/16
RR 22 5/16


@IndroCruise , my next order of business is checking sensors. What do you make of the fact that no matter how much I raise the sensor, when the car re-levels it consistently reads lower than 0? Seems to be around 8-10 mm off for the fronts every single time.

Repeating my other Qs here:
Q1: Would you recommend testing the rear height sensor in the same way as the front sensors?
Q2: When I remove all the sensors to test them, can I still drive the car (to move it around my driveway)?


EDIT: AHC Active Test worked! I swear I did nothing different, but this time around I was able to raise and lower the front and back. I don't think this changes anything as far as my problem goes, however. I am going to attempt to zero out the height sensors one more time and report back.


EDIT 2: As suspected, after zeroing out the sensor heights and going through another N>L>N cycle, truck settles back in to the same set of numbers:

...And most importantly, the difference in fender heights from before zeroing out and after matches the change in sensor height values above. For example, rear fender height was at 20.5 inches (set using Active Test) prior to zeroing sensor height, and then became 20 inches after - roughly 13 mm. Same with the front, I adjusted the FR/FL to 19 9/16, and now both are sitting around 19 3/16, a difference of 3/8 = 9.5 mm. Therefore it seems the sensors are all reading accurately, but the truck refuses to go back to previously zeroed heights. What the heck can that mean??

 

[packeted]

@TreatSmash not sure if this is helpful but I did the globes on my 2006 a few weeks ago. I was preparing for a battle but to my surprise they all came off very easily, no need to remove the running boards and minimal PB blaster. I used this fan clutch wrench: Amazon product ASIN B01GDXC4OM - it looks a bit longer than yours so that might be helpful. Make sure the neck is properly seated on the nut part of the globe.

Another strategy I've heard people use is a chisel on the widest part of the globe, hammering counter-clockwise to break it free.

Obviously make sure all the pressure is out of the system before you start!

 

[IndroCruise]

Alright, I am back with some measurements.

First of all, I rechecked the sensor heights today and found:
FR/FL/R
-7.6/-8.0/-13.2
Then I adjusted them to the following:
-12.6/-12.4/-13.2
When I then went from N>L>N, the measurements became:
-9.0/-7.8/-13.2
I then again adjusted the fronts to something close to the rear:
-13.6/-13.2/-13.4
After another N>L>N cycle, I obtained similar results:
-9.2/-7.8/-13.2


These are the pressures (also consistent after each N>L>N cycle):

View attachment 3278000


And these are the current fender measurements - the sides are within 1/8" of each other:
FL 19 5/8
FR 19 9/16
RL 20 1/2
RR 20 3/8


And I am consistently getting the following raise times:
L>N = 19s, with a total of 38s of 'pump noise'
N>H = 7s, with total of 16s of 'pump noise'


I measured the fender heights at H as well, just to see how much height increase I'm getting and if it stays level, and again they are within 1/8":
FL 21 1/8
FR 21 3/16
RL 22 7/16
RR 22 5/16


@IndroCruise , my next order of business is checking sensors. What do you make of the fact that no matter how much I raise the sensor, when the car re-levels it consistently reads lower than 0? Seems to be around 8-10 mm off for the fronts every single time.

Repeating my other Qs here:
Q1: Would you recommend testing the rear height sensor in the same way as the front sensors?
Q2: When I remove all the sensors to test them, can I still drive the car (to move it around my driveway)?


EDIT: AHC Active Test worked! I swear I did nothing different, but this time around I was able to raise and lower the front and back. I don't think this changes anything as far as my problem goes, however. I am going to attempt to zero out the height sensors one more time and report back.


EDIT 2: As suspected, after zeroing out the sensor heights and going through another N>L>N cycle, truck settles back in to the same set of numbers:

View attachment 3278013

View attachment 3278014


...And most importantly, the difference in fender heights from before zeroing out and after matches the change in sensor height values above. For example, rear fender height was at 20.5 inches (set using Active Test) prior to zeroing sensor height, and then became 20 inches after - roughly 13 mm. Same with the front, I adjusted the FR/FL to 19 9/16, and now both are sitting around 19 3/16, a difference of 3/8 = 9.5 mm. Therefore it seems the sensors are all reading accurately, but the truck refuses to go back to previously zeroed heights. What the heck can that mean??

*** Edited and updated for completeness ***

Responding to your Posts #384 and #389 -- in my usual possibly excessive detail -- and including your concern that

"...And most importantly, the difference in fender heights from before zeroing out and after matches the change in sensor height values above. For example, rear fender height was at 20.5 inches (set using Active Test) prior to zeroing sensor height, and then became 20 inches after - roughly 13 mm. Same with the front, I adjusted the FR/FL to 19 9/16, and now both are sitting around 19 3/16, a difference of 3/8 = 9.5 mm. Therefore it seems the sensors are all reading accurately, but the truck refuses to go back to previously zeroed heights. What the heck can that mean??"

Firstly, it is encouraging to see that the Height Control Operation Test, alias “Active Test”, does work. When I have difficulties with this procedure, it usually turns out that I have overlooked selecting COMFORT mode – per Step (c) in my previous Post #382 in this thread, or, the “Active Test” has been blocked by some other fault.

Secondly, I do not agree that it can be deduced from the reported observations and numbers that "Therefore it seems the sensors are all reading accurately".

A positive “Active Test” demonstrates that the Height Control Operation is capable of working, which means that all the relevant fuses and relays and the power supply needed for AHC operation are healthy. That means that attention should be directed elsewhere.

The concern then is that there is one (or more) interferences, most likely from one or other of the Height Control Sensor circuits, which is preventing the Suspension ECU from causing the vehicle to self-level to the point at which the Height Control Sensors read zero +/- 5 millimetres or +/- 0.2 inches at N height – and then the vehicle should be at your chosen and set ‘ride height’ at N -- and it should stay there!

This is what the AHC system is designed to do consistently and repetitively in real time whenever the vehicle is operating -- and this is the reason the system is called Active Height Control.

Except that your vehicle -- 2006 LX470 with about 135,000 miles, located in Northern California -- does not do this, despite your considerable efforts!!

Causes other than the Height Control Sensor circuits are possible – but given all the symptoms, and assuming that you are very sure that you do not have air trapped in the AHC system, the alternatives (such as AHC Pump impaired by partial internal blockage, Height Control Accumulator not participating in the raise function correctly, or faults in the Suspension ECU itself) all seem less likely than issues within the Height Control Sensor circuits, meaning the Sensors plus the Connectors plus the Wiring Harnesses.

Your Q1: “Would you recommend testing the rear height sensor in the same way as the front sensors? Are they substantially the same mechanism? -- In other words, is it a foregone conclusion that the sensor itself is bad? Just wondering before I spend $230 for a new OEM sensor off ebay”?

Yes, it is reasonable to remove, disassemble, clean and test the Rear Height Control Sensor -- and both Front Height Control Sensors as well. The linkages are slightly different but they are all simple potentiometers as depicted below -- no modern electronics within these devices on LC100/LX470 -- and they all operate in the same way.

These Sensors are robust, very long-life components but they do wear out -- like brakes and the braking system, tyres, timing and other belts, steering rack, mechanical suspension parts, bushes, etc, etc, etc -- and your Sensors already are 17 years old (although quite low mileage).

You have been working on the Sensors so is it fair to assume that the linkages on all three Sensors are in good visual condition -- not detached, broken or impaired by corrosion?

Inside the Sensors, the internal carbon track develops ‘wear zones’ (particularly in the area corresponding to N height because there is constant movement there), the contact with the carbon track by the tiny brushes slowly weakens, moisture ingress leads to corrosion of the internal contacts which look like small coil springs causing increased resistance or even open circuits and/or ‘tracking’ due to moisture leads to reduced resistance or even short circuits. Any of these will affect the output voltage from the Sensor which then results in incorrect voltage signals to the ECU -- see correct voltages far below. In turn, this may result incorrect directions by the ECU to the AHC Pump and/or the Levelling Valves in the Control Valve Assembly, causing strange behaviors by the vehicle at the Front or Rear or both.

This response is caused by the actual voltage signal the ECU receives from the Sensor. The ECU then operates the AHC Pump to increase height (Front and/or Rear), or, opens the relevant (Front and/or Rear) Levelling Valve to release AHC Fluid to the AHC Tank and reduce height.

The point is that the ECU attempts to cause the Front and Rear to raise or lower until the correct voltage signal is received for N height (or LO or HI height if those are selected). This is the basic underlying principle of this circuit.

The response can be erratic when the ECU receives widely different signals from each Sensor circuit, outside the acceptable tolerance of the ECU. The ECU may then cause the Front and Rear of the vehicle to do different and unexpected things -- such as the behaviours and differences in readings you are observing – because the Suspension ECU is unable to resolve conflicting signals from the Height Control Sensors.

The overall Height Control Sensor circuit must be considered -- more about that later – but start first with the Sensors themselves ….

Disassembly and internal inspection of each Sensor is a good idea – but frankly, inspection by eye alone is insufficient. Actual electrical testing per FSM is important to see whether there actually is a smooth gradation in voltage output through the range of the Sensor movement (or there is an alternative method which looks for a smooth gradation in resistance -- High as a kite, hard as a rock! (Yes AHC again...) - https://forum.ih8mud.com/threads/high-as-a-kite-hard-as-a-rock-yes-ahc-again.1119157/#post-12149330 ).

You have asked Q2: “When I remove all the sensors to test them, can I still drive the car (to move it around my driveway?”

I don’t know because I have not tried this. However, the Levelling Valves (located in the Control Valve Assembly) are “normally closed” and remain so in the absence of signal to open from the Suspension ECU. When the Levelling Valves remain closed, AHC Fluid cannot return to the AHC Tank from the 'shock absorbers' (actually struts!) and the vehicle height cannot change. If you simply disconnect the Sensor (creating an open circuit in any of the three Height Control Sensor circuits), that is likely to initiate the ‘fail safe function’ and Diagnostic Trouble Code DTC C1711, or C1712, or C1713, any of which ordinarily would cause the vehicle to adopt N height -- but given the current spurious behaviour of the vehicle it is unclear what actual hub-to-fender height would be the result! However, the vehicle should still be drivable whatever it does, even it drops to the bump stops.

Alternatively, the AHC system can be de-activated (and will do nothing) by pulling the 15 Amp AHC-B Fuse and the 20 Amp AHC-IG Fuse, both located behind the LHS cover in the (LHD) Driver’s footwell just forward of the LHS Front Door.

As described back at at Post #368, in normal operation there may or may not be a DTC associated with a fault in the Height Control Sensor or its electrical circuit back to the ECU, depending on the nature of the fault. Absence of a DTC does not provide assurance of healthy Sensors.

The reliability of old Sensors is highly questionable because even if they currently test OK, they are not going to last forever -- which is why replacement usually is a good idea, either as a potential ‘fix’ of a current failure or as a pre-emptive measure against inevitable future failure.

If this were my vehicle, I would electrically test all Sensors (starting with suspicions about the Rear Sensor) and if in any doubt I would replace the Sensor(s) -- expensive as that may be, using only Toyota/Lexus or AISIN replacements, not second-hand or unreliable cheap fakes. The Part Numbers are given here:

Height control sensor

I have been doing my annual AHC maintenance and have run into an issue with my right front height control sensor. It all seems to run fine, but when I hook up Techstream and try to adjust that sensor it will only show -26-0 on the whole movement of the slide. no positive numbers at all. Does...

forum.ih8mud.com

I would also remain aware that there can be broken wires in the electrical harness (meaning the Height Control Sensor circuits), especially around the junction blocks.

The symptoms of a broken wire(s), including erratic height behaviour, will be the same as a fault in the Sensor itself.

It is worth making sure that the Sensors are healthy before embarking on the arduous detective work to find a wiring break. Broken wire diagnosis involves obtaining the relevant section of the Electrical Wiring Diagram and testing for continuity step by step, from junction to junction, through the circuit -- including as mentioned previously, all the way back to the now-infamous BI1 connector block high up in the LHS rear quarter panel as highlighted by @suprarx7nut and @2001LC, as discussed in post #9 and other posts in the following thread:
AHC done? - https://forum.ih8mud.com/threads/ahc-done.1299423/#post-14719487

If not studied previously, may I also commend to you the following LC100 on-line references? There is no difference between the AHC and TEMS systems where fitted to LC100 and the AHC and TEMS systems fitted to LX470:

General Description of the AHC/TEMS systems with explanations and diagrams of components:

LC100 Workshop Manual - https://lc100e.github.io/,
then scroll down through the index panel on the LHS of the opening page:
+ New Car Features
+ CHASSIS
+ Suspension
+ Active Height Control and Skyhook TEMS

Scrolling to “Repair Manual” and “DIAGNOSTICS” reveals relevant diagnostic and test information, etc. For example:

LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ DIAGNOSTICS
+ ACTIVE HEIGHT CONTROL SUSPENSION & SKYHOOK TEMS
+ C1711/11 to C1713/13 -- for test procedures concerning Height Control Sensors

Scrolling to Electrical Wiring Diagram and visually tracing the circuits helps with understandings:

LC100 Workshop Manual - https://lc100e.github.io/
+ Electrical Wiring Diagram
+ OVERALL ELECTRICAL WIRING DIAGRAM (LHD)
+ Active Height Control Suspension
+ Choose relevant year -- note: there can be some differences in EWD's for LC100 and LX470

Scrolling to “Repair Manual” reveals settings, repair information etc. For example:

LC100 Workshop Manual - https://lc100e.github.io/
+ Repair Manual
+ SUSPENSION AND AXLE
+ ACTIVE HEIGHT CONTROL SYSTEM
+ ON-VEHICLE INSPECTION

Here are a few pics:

Height Control Sensor voltages at LO, N and HI:

AHC Fuse Locations:

 

[usedname]

THank you @IndroCruise , will report back.

In the meantime, should I wind down the torsion bars a bit? I had wound them up several turns each when I was trying to cross-level. It looks like my front pressures are lower than they should be, and I take it that it is not our assumption that there is anything wrong with the pressure sensors? Just wondering if the torsion bars taking up too much of the load would provide slightly harsher ride (which I experience in particular with rough roads / abrupt transitions).

 

[IndroCruise]

THank you @IndroCruise , will report back.

In the meantime, should I wind down the torsion bars a bit? I had wound them up several turns each when I was trying to cross-level. It looks like my front pressures are lower than they should be, and I take it that it is not our assumption that there is anything wrong with the pressure sensors? Just wondering if the torsion bars taking up too much of the load would provide slightly harsher ride (which I experience in particular with rough roads / abrupt transitions).

I have edited my long Post #391 in this thread to try and make the reasoning more clear ....

I have read your reports carefully. It remains my strong opinion that it is EXTREMELY LIKELY that you have problems with

• at least one of the Height Control Sensors, or,
• at least one of the Height Control Sensor circuits at some as yet unknown point.

Testing of the Sensors is essential, and if they prove OK (and I remain suspicious of your rear Sensor), then investigation of the Height Control Sensor circuits then becomes essential.

Yes -- the Front AHC pressures are low in some of the screenshots and low AHC pressures will inhibit damping and best ride comfort. If that was caused by unbalanced cross-levelling, then correction would entail both torsion bar adjusters being wound counter clockwise by equal amounts to achieve increased Front AHC pressures within the FSM-specified range at N height, then re-checking cross-level per the attached FSM extract below.

But there is a catch here ....

Please be aware that correction of AHC pressures depends indirectly on the correct operation of the Height Control Sensors when using the the hand-held or Techstream method for reading pressures.

The AHC Pressures increase with increasing height, decrease with decreasing height.

Currently the vehicle is unable to self-level reliably to the expected N height and instead ultimately arrives at a lower height than expected at the N setting, with all Sensor readings negative. Until this is resolved, the hand-held or Techstream method of reading AHC Pressures will be unable to reliably indicate the actual AHC pressures at the height at which the vehicle settles following the N > LO > N movement, because N height is not as expected and is unreliable.

High range pressure gauges could be used at the bleeder valves to measure actual AHC Pressures reliably and directly.

Frankly, the first order of business needs to be resolving issues in the Height Control Sensors or the Height Control Sensor circuits, or, eliminating them as a cause with testing and investigation.

 

[usedname]

Yessir. Sensor(and if they check out, circuit)-testing next.

 

[IndroCruise]

Yessir. Sensor(and if they check out, circuit)-testing next.

I must offer an apology -- I recognise that I have dumped a HUGE download of information on you in a couple of my habitually very long posts with references and attachments, over just a few days. I have to confess that it has taken me about 5 years, not just a few days, to learn the AHC/TEMS systems (and I am still learning) mainly by reading and writing on this forum and working on my vehicles (or looking over the shoulder of independent mechanics). I do have an engineering background -- which gives me just enough ancient knowledge to be dangerous!

There were and are many mentors -- in my case very longtime and very capable member @uHu pulled me into line and put me back on track more than a few times – and there are many others:

Definitive list of AHC maintenance items - https://forum.ih8mud.com/threads/definitive-list-of-ahc-maintenance-items.604577/page-32#post-12550071

The point is that the AHC and TEMS systems are learnable -- which is just as well because it usually is hard to find good experienced advice about these systems on the ground, almost anywhere in the world! This is really strange – because these are easy systems compared to most other things on the vehicle – think ABS brakes, VRGS, ATRAC, auto transmission, engine management, fuel injection -- the list goes on.

Your vehicle is young -- 2006, only ~135k miles -- and looking beyond the current frustrations (which will be resolved!!), it has a very long remaining life ahead.

Hang in there!! Keep using this forum, then much more will be revealed ….

 

[usedname]

I must offer an apology -- I recognise that have dumped a HUGE download of information on you in a couple of my habitually very long posts with references and attachments, over just a few days. I have to confess that it has taken me about 5 years, not just a few days, to learn the AHC/TEMS systems (and I am still learning) mainly by reading and writing on this forum and working on my vehicles (or looking over the shoulder of independent mechanics). I do have an engineering background -- which gives me just enough ancient knowledge to be dangerous!

There were and are many mentors -- in my case very longtime and very capable member @uHu pulled me into line and put me back on track more than a few times – and there are many others:

Definitive list of AHC maintenance items - https://forum.ih8mud.com/threads/definitive-list-of-ahc-maintenance-items.604577/page-32#post-12550071

The point is that the AHC and TEMS systems are learnable -- which is just as well because it usually is hard to find good experienced advice about these systems on the ground, almost anywhere in the world! This is really strange – because these are easy systems compared to most other things on the vehicle – think ABS brakes, VRGS, ATRAC, auto transmission, engine management, fuel injection -- the list goes on.

Your vehicle is young -- 2006, only ~135k miles -- and looking beyond the current frustrations (which will be resolved!!), it has a very long remaining life ahead.

Hang in there!! Keep using this forum, then much more will be revealed ….

Not at all! Part of the value you're providing is your stepwise/deductive/inferential approach. I am carefully reading everything you are posting, and I have a sneaking suspicion I will eventually pony up the cash to get the FSM in physical form. Nonetheless I'm happy to be spoonfed at this stage and it's a great assurance that there is someone out there who I can turn to with further problems or surprises.

--

Alright, here is the rear sensor - immaculate on the inside. The connector was also clean. Any of the crud on the face is just dirt that fell in when I separated the cover.

As for proper testing, I rigged up 3 fresh AA batteries using a bunch of alligator clips and neodymium magnets. The series voltage was something like 4.7v, so it's reasonable I think that I was getting 4.18V at H.

Since the sensor is off the truck I didn't know where N would approximate in the travel of the sensor arm, but I don't think that matters, because voltage change was smooth throughout the entire travel from H to L. What I found was that there is a little bit of travel area in which the voltage at H is constant at ~4.15V. Similarly, there is an area on the L side where voltage is constant at around 0.45V. However, what I also found was that at the very end of the travel, the voltage drops further from a constant of 0.45V to around 0.28V. The following two photos are the arm at the beginning of the 0.45V area, and the end of the 0.45V area. In other words, there is about 1mm of further travel left where the sensor output drops below specified the L voltage.

Looking back at the photo of the substrate, it seems to me that the raised trapezoidal sections that begin outside the 90 degree marks (that you've annotated with a dotted red line on your picture) are these same areas of constant voltage, and, if we look at my picture, it appears that my brushes travel beyond the lower raised trapezoid - I'm fairly sure this is why voltage is dropping further than the 0.45V specified on the L end. Is this salient? It might be. I'm going to try to shim the 'stop tab' with maybe 1.5 mm of material, so that the brushes do not travel beyond the constant voltage area.

 

[usedname]

In case I wasn't being clear:

Without really any clear rationale, I think it's conceivable that when the sensor circuit receives a voltage X volts outside spec upon going to L
(in this case 0.45V - 0.28V = 0.17V), it would then do some kind of algorithmic/logical operation that would result in it targetting the wrong voltage when it returns to N - something like N volts minus X. Probably much more complex than that, but this really might be AN answer if not THE answer.

 

[IndroCruise]

In case I wasn't being clear:
View attachment 3280012

View attachment 3280013


Without really any clear rationale, I think it's conceivable that when the sensor circuit receives a voltage X volts outside spec upon going to L
(in this case 0.45V - 0.28V = 0.17V), it would then do some kind of algorithmic/logical operation that would result in it targetting the wrong voltage when it returns to N - something like N volts minus X. Probably much more complex than that, but this really might be AN answer if not THE answer.

Good to see you getting involved in the detail!! In your pictures of a Sensor, the connector and the swing arm uniquely identify this as the Rear Height Control Sensor.

As a starter and getting into even more detail, I notice in the second picture in your Post #397 the question with an arrow “What is this?”

So let me start with that -- because it also helps explain some of the issues you are investigating.

I will use RH Front Height Control Sensor pictures as illustrations because I have these on file and I don’t have a helpful picture of a Rear Sensor. The chassis mounting, the socket to receive the harness connector and the swing arm and linkage obviously are different on the Front Sensors compared to the Rear Sensor but the operating principles as simple voltage dividers (potentiometers) are the same.

The manufacturer -- most likely stamped as AISIN or TOYOTA on an OEM Sensor -- uses a tiny plastic slider and temporary plastic post at the factory to set the mid-point of the swing of the Sensor arm to give a signal of about 2.25 volts, corresponding to the N height setting, as designated in the FSM.

Why does this exist?

As can be imagined when looking inside the Sensor, there is likely to be some variation in manufacturing of the "carbon track" and also in the positioning of the sliding brushes and other parts. One Sensor can be slightly different from another -- and readings are sensitive within fractions of a volt.

This arrangement allows the Sensor manufacturer to test and position the Sensor arm at the correct voltage of about 2.25 volts (or the correct equivalent resistance) for N height at or very close to mid-swing of the Sensor as it moves through its arc.

This arrangement aids quick assembly, within seconds on a production line, to match the correct Front and Rear ‘ride heights’ of the vehicle at N height setting, with minimal, if any, subsequent adjustment.

When the Sensor is installed and operating on the vehicle a little further down the production line, the temporary plastic post described will break and become redundant and of no further use.

If the plastic slider to which the plastic post was attached remains in place, the ‘factory set’ position of the now-missing plastic post, correct for N height on a stock vehicle, can be identified. This can be considered when adjusting Sensors, long after the vehicle has left the factory. This situation also can be quite useful when replacing Height Control Sensors with new units with the temporary plastic post still in place, as seen in one of the above pictures.

If plastic slider has moved, as in your case, it may be a little more difficult but the approximate mid-swing position can still be worked out by examining the above pictures. The diagrams in relevant section of the FSM “DIAGNOSTICS” section -- extract attached -- also help. (These can be expected to be accurate in the Japanese manner, not haphazard sketches).

I would also suggest that, given the mid-swing position, both the LO and HI positions also can be estimated, about 45 degrees either way from the N position.

With all of that in mind, what actual voltage are you measuring with your apparatus at N (mid-swing) position?

Your results for the actual measured voltages at the LO and HI positions seem very close to the FSM-specified values. You report that the voltage transitions are smooth from LO to HI.

This is leading to a conclusion that at least your Rear Height Control Sensor is healthy at the moment. Unless tests of the Front Height Control Sensors give adverse results, the next conclusion would be that it is time to check the harnesses for broken wires, especially in the regions of connectors and junction blocks.

It is much less than rigorous, but given the multiple reports by others of weaknesses at or near the BI1 connector as mentioned in my previous posts, one thought might be to use the multimeter to read the voltage coming from the harness (Ignition ON, Engine OFF -- while the Rear Sensor is removed) and to reach up to the BI1 connector block, move it around to see whether the voltage changes at the multimeter, which could suggest broken wire(s). Obviously if doubt exists, proper testing is necessary. Inspection of the FSM Electrical Wiring Diagrams (EWD’s) will reveal other connectors right through to the Suspension Electronic Control Unit which may be problematic – it is just that BI1 connector has been topical in recent times.

If your hypothesis of “some kind of algorithmic/logical operation” holds, then that would translate to me as a defective Suspension ECU! Possible but unusual -- hopefully not the case on your vehicle!

 

[usedname]

...

I will get back to you with N-approximated voltage.

I didn't mean that I anticipate there is something wrong with the ECU, rather that it might be doing the best it can when it receives a voltage outside spec (in this case 0.28v instead of 0.45v). I'll shim the 'stop tab' to prevent it from going to that extent and see if that makes any difference in the behavior, then move on to the front sensors, and then to testing the circuits. I checked out BI1 and BI2 in the rear quarter, they appear to be easily reachable.

One odd thing is that it seems that the diagram of the sensors you've provided shows the limits of clockwise travel as HI and anticlockwise as LO... but this was opposite of what I observed. I connected the batteries correctly - positive end to pin 1, negative to pin 3, and the multimeter was connected correctly as well, testing between pins 2 and 3. Besides, if the multimeter was connected reversed it would just show negative voltage, not inverse voltage. (Does a potentiometer work in reverse polarity?)


Edit:
Exactly on spec when hole for plastic peg is directly above it's holder in the slider - which means the slider is still in the place where it was set at the factory.

Shimming with a bit of a windshield wiper insert:

 

[usedname]

Alright, FL sensor had a very large dead area in the >N region. I opened it up and it appeared that the brushes were no longer contacting... so I bent them back up a bit. After putting the cover back on, I think they are functional, with smooth voltage change throughout the range, except that much like my rear sensor, the brushes travel beyond the known 'H' area and go from spec 4.05v to 4.22v at the limit. I wonder if this matters. Suspect my fix is only temporary, but will check FR sensor and then put them all back on and see what happens.