The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (2 Viewers)

[uHu]

Reading this thread again for a bit - there's a lot going on I see. Looks like you are on the right track, usedname. Regarding your worry about the voltage at the areas at the ends of the travel of the sensors: There is no need to worry. What happens to the voltage (or resistance) at the ends doesn't matter much, because the active suspension movement will have stopped already when the right voltage is reached.

Shimming or modifying the end stops is not a good idea, as the suspension arms, and sensor links, can actually move a bit beyond what is controlled by the AHC, if you lift a wheel or compress a bump stop. So I would leave them alone, not to risk any bending of the sensor arms.

Looks like you found a problem that could be the whole cause of the "non-zero-adjustment", but better check the other front sensor as well. And you are right in expecting having to replace the sensor. They do wear out, and the AHC ECU is very particular about getting a stable signal from the sensor. Any tiny fluctuation (when there shouldn't one) can give a harsh ride as the ECU might interpret it as a bumpy road.

I think a happy AHC owner is one who has a couple of spare sensors in stock

Just thought I would jump in until Indro is back, but thinking of the rotation of the earth (timezones) I believe he will be back before you read this anyhow.

 

[IndroCruise]

Reading this thread again for a bit - there's a lot going on I see. Looks like you are on the right track, usedname. Regarding your worry about the voltage at the areas at the ends of the travel of the sensors: There is no need to worry. What happens to the voltage (or resistance) at the ends doesn't matter much, because the active suspension movement will have stopped already when the right voltage is reached.

Shimming or modifying the end stops is not a good idea, as the suspension arms, and sensor links, can actually move a bit beyond what is controlled by the AHC, if you lift a wheel or compress a bump stop. So I would leave them alone, not to risk any bending of the sensor arms.

Looks like you found a problem that could be the whole cause of the "non-zero-adjustment", but better check the other front sensor as well. And you are right in expecting having to replace the sensor. They do wear out, and the AHC ECU is very particular about getting a stable signal from the sensor. Any tiny fluctuation (when there shouldn't one) can give a harsh ride as the ECU might interpret it as a bumpy road.

I think a happy AHC owner is one who has a couple of spare sensors in stock

Just thought I would jump in until Indro is back, but thinking of the rotation of the earth (timezones) I believe he will be back before you read this anyhow.

So @usedname, you now have the very welcome voice of considerable knowledge and experience from @uHu in Norway -- he has been a reliable guide to us all on AHC/TEMS matters and other issues for many years. A search on this forum for “height sensors” or just “sensors” and @uHu will reveal more insights and pictures.

As @uHu mentions, it is best to be avoid shims etc impeding movements so that the Sensor linkage has more freedom of movement relative to the Upper Control Arm and the ‘shock absorbers’ than is required by the mechanical suspension. Restrictions may damage the Sensor linkage or the Sensor itself.

In this vein and with the experience now gained, it is worth another look at what the FSM has to say about the Height Control Sensors:

It can be seen that the ECU may not respond, and is designed not to respond, to excursions of short duration (such as a ‘bump’) outside the specified voltage range of 0.3 volts to 4.7 volts -- and the intended actual working range of the Height Control Sensor circuits is smaller than this limit -- FSM-specified as at 0.45 volts to 4.5 volts.

The ECU will respond to an “abnormal signal continued for 1 second at vehicle speed of 8 kph (5 mph) or more” AND the “abnormal signal …. is detected (checked) every 0.01 seconds …. and continued for 0.02 seconds”.

If the “DTC Detecting Condition” is reached, then the ECU will record a DTC code and also initiate the “Fail Safe Function” defined for this specific condition. The designer did not intend that the system be merely 'bumped' into 'fail-safe function' -- and certainly in my own experience the system has proven to be robust and reliable in very tough conditions, if the system is well-maintained.

As mentioned previously -- and as I suspect you are discovering -- if a fault that causes a signal of required duration, within the prescribed voltage range, but is the wrong signal for the actual height of the vehicle, then a DTC may not be recorded and the defined ‘fail safe function’ may not be initiated -- but a fault definitely is present. Such a fault would be due to the resistance within the Sensor being higher or lower than ‘as manufactured’ due to wear and tear, moisture, corrosion or whatever, or, by problems of resistance or poor continuity somewhere in the wiring harness, meaning the overall Height Control Sensor electrical circuit.

The Japanese-to-English translation suffers a bit in the FSM wording, but the gist of it is clear. It is also very clear that the ECU is very fussy about the signals received from each Height Control Sensor circuit. Resolving very different signals from different Sensor circuits will be problematic for the ECU at N height (or LO or HI height if selected at the console switch) and easily can result in strange behaviours of the AHC system, including strange Front and Rear heights adopted by the vehicle, with or without a DTC.

Toyota/Lexus tells us little or nothing about the internal hardware and software of their proprietary Suspension ECU and how it is built and programmed. All that can be done is to avoid speculation and make careful observations and look for actual data -- which is what you are now doing.

Hopefully your work on the actual Sensors and/or the Sensor circuits resolves the issues on your vehicle!

If not, it will be necessary to look further afield.

However, it is pointless to speculate or dive into more complexity without first being confident that the Height Control Sensor circuits are in good order.

The AHC/TEMS systems are ancient technology by modern standards, with the system development dating back more than 30 years to the mid-1990’s. When the systems and components are in healthy condition, the LC100/LX470 version of AHC/TEMS still works remarkably well, even when compared to more modern evolutions.

Keep going!!

 

[usedname]

...

Roger that, I thought I was quite clever, but seeing that both the other sensors had the same characteristic of going 'over', I sheepishly pried off my shim.

Sensor update:
-FR and RR sensors were fine; FL had a problem with no contact that I think was fixed by bending the brushes, and I rechecked the voltage output afterwards and found it to be smooth.
-Ran Active Test again. Set front height to 19.75, rear to 20.5.
-Zeroed sensor heights.

Aaaand after an N>L>N cycle:

At least the fronts match now, which suggests to me that the brush fix is working for now.
Opinions? Are you still more suspicious of the sensors or the circuits?
Definitely replace the FL sensor? Move on to circuit testing? Any pointers on testing continuity or likely suspects aside from BI1/2?

I will next try what @IndroCruise suggested earlier in the thread w/r/t BI1:

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 that doesn't work, then I suppose it's time to closely consult the wiring diagrams and find the additional junction boxes and start continuity testing. I haven't done this before but I get the concept. Currently reading the posts you linked to earlier in the thread regarding BI1.

AHC done?

Let me start by saying I love my AHC. I love the ride, I love the tune-ability and I like the up and down. 1999 LX470 with a little over 400,000 miles. It’s broke and can’t fix it. Now the backstory - we had a huge rainstorm and I am guessing the sunroof drains couldn’t handle the water (they...

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

Many of the Toyota AHC fluid in black plastic 1 liter bottles, have been found to have jelled. Seems mid to early 2021 (a lot of reports out of TX), have jelled. It may have to do with plastic reaction with the fluid. Toyota witched back to the 2.5 liter tin cans, mid to late 2021.. I have 2...

forum.ih8mud.com

 

[usedname]

Probably been posted before but in reviewing the AHC diagnostics (from the service manual) posted previously by @IndroCruise, came across this:

Check for open and short circuit in harness and connector between height control sensor, fluid pressure sensor, fluid temp. sensor and suspension control ECU (See page INï35).

Referring back to that section of the manual, (attached pdf) it goes in detail over checking continuity, open circuits, short circuits. Still pretty daunting and right now I'm hoping it's just a connector/continuity problem!

Eye opening thread about BG1/BG2 damaged upstream of BI1/BI2! Gives a working idea of electrical problem-solving.

MY06LX EWD needed badly

If anyone has a link to it?, ... need to trace AHC ECU harness from ECU connectors to damping force actuators, and the connectors at ECU are not marked ... need back of AHC ECU connector view. Thx!

forum.ih8mud.com

 

[usedname]

Well, I checked out BI1/BI2/BI3. I had a heck of a time prying them open. They all looked good. I was almost disappointed, I was hoping I'd finally find the culprit.

There is another unnamed connector right next to those three that in mine is used for trailer wiring and also for power for a 'K40' rear radar detector (came installed). Just putting this up in case you guys think this might be a problem (but I don't think so...).

Also tried to find BG1/BG2. Felt along the top of the passenger side rail along the area of the exhaust, and didn't feel anything melted/fried.

BF3 is a blue connector in the cluster of wiring where the jack goes; I can see it but I held off on digging it out, looked tedious. I couldn't find BF4 or BF5.

Then BD1 and BD2 are grey connectors visible from the driver's rear wheel between the wheel well and the frame rail. Again, cables going to and from appeared okay but I held off on doing surgery on the wheel well in order to extricate the connectors.

I'm kind of stuck. I reseated BI1, BI2 and BI3, and it didn't fix my issue. I'm looking for some guidance in terms of what to actually investigate and how...

 

[usedname]

The reason I was looking at all these connectors (BG1/2, BF1/3/4/5, BD1/2, ID6) is because they are upstream/downstream of BI1/BI2 and also most of the AHC system, and were implicated in previous posts. But most are related to the damping force control, not the sensors. I was wondering if it would be better to check the ones that are way upstream of the sensors, such as ID4, which pops up in the sensor circuits prior to connecting to the Suspension Control ECU, or the 7C/7D relay, which is also part of these same circuits. These also have the benefit of being more accessible..

Looks like ID4 is in the left kick panel. Relay 7C/7D behind the glovebox.

@IndroCruise or @uHu (or @PADDO ?) am I on the right track? Where would you suggest starting to check for continuity? All the way from from BI1/BI2, or the sensors, to ID4 and relay 7? (Suddenly throwing a few hundred at new Aisin sensors 'just in case' is looking like a better option than testing circuits. But it certainly seems like the sensors themselves are fine...)

Most of all I'm baffled by what the heck could it mean when the system seems to work just fine - active test, cycling through LO/N/HI in reasonable times, 10+ gradations, selectable SPORT/COMFORT dampening that is discernible on the road - but consistently refuses to return to the zeroed N height!

 

[IndroCruise]

The reason I was looking at all these connectors (BG1/2, BF1/3/4/5, BD1/2, ID6) is because they are upstream/downstream of BI1/BI2 and also most of the AHC system, and were implicated in previous posts. But most are related to the damping force control, not the sensors. I was wondering if it would be better to check the ones that are way upstream of the sensors, such as ID4, which pops up in the sensor circuits prior to connecting to the Suspension Control ECU, or the 7C/7D relay, which is also part of these same circuits. These also have the benefit of being more accessible..

Looks like ID4 is in the left kick panel. Relay 7C/7D behind the glovebox.

@IndroCruise or @uHu (or @PADDO ?) am I on the right track? Where would you suggest starting to check for continuity? All the way from from BI1/BI2, or the sensors, to ID4 and relay 7? (Suddenly throwing a few hundred at new Aisin sensors 'just in case' is looking like a better option than testing circuits. But it certainly seems like the sensors themselves are fine...)

Most of all I'm baffled by what the heck could it mean when the system seems to work just fine - active test, cycling through LO/N/HI in reasonable times, 10+ gradations, selectable SPORT/COMFORT dampening that is discernible on the road - but consistently refuses to return to the zeroed N height!


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May I suggest also tagging @2001LC and @suprarx7nut and @Moridinbg -- -- and also inviting the wise insights of any other IH8MUD Members. Their wide experience also may be useful here ….

@usedname -- For my part, I admire your work and persistence. You have gone much further than many others!!

To summarise the story so far -- assuming that I have gathered your data accurately from your several posts ….

After all attempts to

--- stabilise the Front and Rear tape-measured hub-to-fender ‘ride heights’ of the vehicle at preferred settings of Front 19.75 inches and Rear 20.50 inches,

and,

--- have the vehicle self-level itself with Front and Rear Height Control Sensor readings close to zero,

the vehicle then drops to significantly lower hub-to-fender heights and the Sensor readings are significantly negative, all as listed below.

AHC pressures also are suspiciously low -- although this might be an effect (or cause?) of the reduced height.

The task is to find and rectify the cause of this behaviour.

So far ....

You have removed, dismantled, inspected, cleaned and electrically tested per FSM battery method all three Height Control Sensors -- and thereby “certified” the health of the Sensors themselves. They may not last forever but at the moment the Sensors themselves appear to be good.

You have correctly cross-levelled the Front of the vehicle using the torsion bar adjusters.

You have used Height Control Operation Test, alias “Active Test” to set your preferred ‘ride heights’ of the vehicle (using the @PADDO recommendation on IH8MUD):

Front: 19.75 inches
Rear: 20.50 inches

At this point, you have set the Height Control Sensor adjusters to zero +/- 5 millimetres or +/- 0.2 inches, as read on Techstream.

No DTC’s are recorded by Techstream.

On testing for AHC pressures, or simply checking ‘ride heights’, the vehicle refuses to return to the null position at N after N > LO > N test movements.

Instead, Height Control Sensor readings on Techstream are not near zero, instead readings settle after driving to:

FR = negative 6.8 millimetres
FL = negative 6.8 millimetres
Rear = negative 12.8 millimetres

and ‘ride heights’ settle to

Front Hub-to-Fender Height = ~19.25 inches (equal both sides)
Rear Hub-to-Fender Height = ~19.75 inches (equal both sides)
(with some variation between tests of up to +/- one-eighth (0.125) inch)

Front AHC pressure after attempted N > LO > N = 5.6 Mpa
Front AHC pressure after attempted N > LO > N = 6.2 Mpa

Raise time: L>N = 19 seconds, with a total of 38 seconds of 'pump noise'
Raise time: N>H = 7 seconds, with total of 16 seconds of 'pump noise’.

Difference in AHC Fluid levels at AHC Tank, HI to LO = 10+ graduations
(this reading is a guide only -- may not have been taken at conforming AHC pressures)

Other details on Techstream screenshots (where provided) after N > LO > N appear normal.
(By the way, best if full screenshots are always provided for full information, not cropped)

Still no DTC’s recorded by Techstream.

Some comments -- hopefully others can add to these and/or please correct any errors or mistaken assumptions on my (@IndroCruise ) part:

Locating, opening, inspecting and closing connectors in the Height Control Sensor circuits such as BI1 and BI2 is a very good thing to have done.

May I very respectfully suggest that this is necessary but insufficient -- because a clean connector is encouraging but that is not enough to “certify” the Height Control Sensor circuit.

By itself this does not tell whether there is/are broken or damaged wire(s) somewhere on either side of any junction causing problems with continuity, resistance or voltage in the circuit -- and ultimately causing incorrect signals to the Suspension ECU and resulting in the problem behaviour of the vehicle.

May I now suggest that the search for broken or damaged wires requires further action -- including methodical testing as set out in the FSM attachment added by @usedname at Post# 404 (added again below for convenience). In effect, Section 1 of this procedure has been done – even more important are sections 2, 3, 4, 5, 6, 7 and ultimately section 8. (It would be easy to jump to a conclusion that there is an ECU problem -- but I would recommend arriving carefully and methodically at that conclusion.

The last thing wanted is to install replacement parts only to endure an unchanged problem because the cause is elsewhere. How do I know this? Because without checking out the circuits, I replaced all three Height Control Sensors on my vehicle in the hope of chasing down a similar fault and also because the Sensors were old and I wanted long term reliability – good idea, good long term maintenance, no regrets -- but it made no difference to the Height Control problem I was chasing at that time!!!!

Where to do next?

Subject to better advice from others, my suggestion is to start at the harness plug at the connector at the each Height Control Sensor itself and work towards the Suspension ECU, firstly testing the overall circuits between these two points for each of the three Sensor circuits -- and if a fault is indicated in any circuit, then test at each junction, step by step, as you go from the Sensor to the ECU -- and sadly this does include the pain of reopening BI1 and BI2.

You could go the other way -- from the ECU back to the to each Sensor. My instinct would be to check the most exposed parts of each circuit first – it would be supremely unlucky to have developed a fault in protected positions such as behind the front internal kick panels (for example connector ID4 as mentioned) and in the dashboard (for example connector, not a relay, 7C/7D as mentioned), unless previous work has dislodged something or unless the relevant junction boxes have been affected by a water leak or other accidental damage.

My instinct also would be to focus on “certifying” all three Height Control Sensor circuits, from each Sensor to the ECU, before branching out to other circuits.

I may well be missing something -- or not according enough attention to other possible causes of the symptoms and data listed far above -- hopefully, others will offer thoughts and corrections if that is the case.

Rightly or wrongly, based on my understanding of the symptoms and the data, I have discounted the following -- in part because

1. None of the height-related or pressure-related DTC’s and related symptoms are present, specifically, C1711, C1712, C1713, C1718, C1731, C1732, C1733, C1734, 1736, C1751, C1762, C1763, C1764, as set out in the FSM DIAGNOSTICS section, and,

2. None of the variations of ‘fail safe functions’ have been initiated by the ECU,

3. AHC and TEMS functions are operating without any of the ‘fail safe’ prohibitions or limitations.

Discounted:

--- air in system or nitrogen from failing ‘globe’ membrane(s) in system -- ‘ globes’ due for replacement?? Indications from test of difference in fluid levels at AHC Tank between LO height and HI height -- reported 10+ graduations, maybe not at FSM pressures but seem OK?? AHC Pump expends effort and pressure in compressing air or nitrogen rather than raising vehicle?? Maybe -- but unlikely -- AHC Pump is positive displacement gear pump, should still achieve required AHC pressures, does so with Height Control Accumulator reaching 10.6 Mpa, so low Front and Rear AHC pressures appear to be related to low height achieved.

--- partial blockage in AHC Pump at internal strainers -- inhibiting flow and pressure from AHC Pump?? Maybe -- but Height Control Accumulator is reaching 10.6 Mpa, so low Front and Rear AHC pressures appear to be related to low height achieved.

--- non-performance of Height Control Accumulator – raise LO > N and N > HI not assisted, raise depends entirely on AHC Pump?? Maybe -- but Height Control Accumulator is reaching 10.6 Mpa, so low Front and Rear AHC pressures appear to be related to low height achieved. Suggest check Height Control Accumulator solenoid by sound and feel during a raise, observe solenoid (SLAC) operation in real time on Techstream during a raise, and/or test per FSM DIAGNOSTICS under DTC heading for C1736,

--- Faulty Pressure Sensor at AHC Pump – maybe -- but would expect at least one definite DTC, perhaps test anyway per FSM DIAGNOSTIC heading for C1718,

--- Faulty Levelling Valves in the Control Valve Assembly – but would expect at least some of relevant DTC’s C1731, C1732, C1733, C1734, AHC prohibited, TEMS locked at hardest (Sport2) setting – none observed. Suggest observe Levelling Valve operation by sound and feel during a raise, observe Levelling Valve solenoids (SLFL and SLRL) operation in real time on Techstream screen during a raise, and/or test per FSM DIAGNOSTICS under these DTC headings,

--- Possible uncertainty about ‘fail safe function’ – the vehicle is not in any ‘fail safe mode’ if the AHC raise/lower system is operational and if the TEMS system is operational. For reassurance, with another person driving, suggest observe in real time on the Techstream screen the operation of “Front Wheel Step” and “Rear Wheel Step”. These refer to the operation of the variable TEMS damping. If a ‘fail safe function’ has been initiated by the ECU, damping will be locked at Step 8 of 16 Steps and will feel rough at low speeds. In a few situations (see Control Valve Assembly) these will be locked at Step 16 of 16 Steps and this will feel very hard. If not in 'fail safe function', varying the console switch through “COMFORT”, “NORMAL”, “SPORT1” and “SPORT2” will vary the range of damping steps used in real time and this will be visible while travelling. When this is done, different combinations of "Damping Force Switch 1" and "Damping Force Switch 2" also will be seen on the Techstream screen -- these are the instructions being given by the ECU to the 'Soft Damping Force Valve' and the 'Hard Damping Force Valve' within the Damping Force Control Actuators (to which the 'globes' are attached). Absence of AHC and TEMS prohibitions by the ECU would show that AHC and TEMS are not in ‘fail safe function’.

 

[usedname]

Thank you @IndroCruise . Everything you've summarized is accurate. (Except that my current ride height is whatever 19.75 inches minus 7 mm, and 20.5 inches minus 13 mm, comes out to - I didn't bother to measure again after obtaining a non-zero result.)

Also thanks for providing your thought process for what you've provisionally ruled out, and where to go next.

-I'm going to make sure steps change with change in damping mode while driving.
-I ordered a hard copy of the EWD, which should be here in a couple of days. Not absolutely necessary to start, but from pictures others have posted, it appears to come in full color which I'd prefer.
-I also ordered some lead extensions for my multimeter so I can reach from the ECU to the sensor and will attempt that next.

 

[suprarx7nut]

@usedname I'd bet $100 your problem is the height sensors. They are precision sensors not meant to be opened or cleaned or re-assembled. There's about a 1% chance anyone is going to open a sensor, fix it and reassemble it in a fashion that actually provides reliable performance. It needs to be replaced with a new genuine OEM sensor.

If the height sensor gives anything less than a perfect reading, you're going to bounce around heights and probably land on a wrong height. Naturally, the "N" range of the sensor is the most worn area. You're experiencing exactly what I'd expect with a dead/dying sensor.

Forgive me if I've missed this, but do you have any current codes or other symptoms beyond the odd N heights?


B1 connector. The connector itself is not to problem - at least not anytime that I've dealt with. Instead, the B1 connector is an awesome place to run multimeter tests. You can test the circuit health with a multimeter from that connector that would otherwise necessitate you pulling the AHC ECU which is a big pain. When I had a bad solenoid circuit I could never find the actual physical problem section of wire. I just ran new wiring and the problem was resolved. For wiring, a DMM is your tool. Not your eyes or fingers.

 

[usedname]

@usedname I'd bet $100 your problem is the height sensors. They are precision sensors not meant to be opened or cleaned or re-assembled. There's about a 1% chance anyone is going to open a sensor, fix it and reassemble it in a fashion that actually provides reliable performance. It needs to be replaced with a new genuine OEM sensor.

If the height sensor gives anything less than a perfect reading, you're going to bounce around heights and probably land on a wrong height. Naturally, the "N" range of the sensor is the most worn area. You're experiencing exactly what I'd expect with a dead/dying sensor.

Forgive me if I've missed this, but do you have any current codes or other symptoms beyond the odd N heights?


B1 connector. The connector itself is not to problem - at least not anytime that I've dealt with. Instead, the B1 connector is an awesome place to run multimeter tests. You can test the circuit health with a multimeter from that connector that would otherwise necessitate you pulling the AHC ECU which is a big pain. When I had a bad solenoid circuit I could never find the actual physical problem section of wire. I just ran new wiring and the problem was resolved. For wiring, a DMM is your tool. Not your eyes or fingers.

Huh, didn't think about the utility of BI1 in that way - a lot of the signals that end up at the AHC ECU go through there. Including the rear height sensor, but unfortunately or fortunately, not the front height sensors.

NO current codes or other symptoms, aside from, I suspect, a rougher ride than the AHC usually provides over smaller bumps.

I WANT to believe that this is as simple as changing out the sensors, but I'm skeptical, mainly because it SEEMS like the sensors read very accurately - they report the height that the truck stops at dead-on each time. Since height is voltage and voltage is height w/r/t the sensors, if the problem was one prematurely reporting that it had reached N voltage, then wouldn't it show a height of 0 mm? Because currently, they all show some negative number that matches the height that the truck lost between setting it up via active test and then going through a N>LO>N cycle.

I mean, I'm aware there's a lot of speculation when it comes to the esoteric workings of the AHC. And maybe it's much less predictable what happens if the voltage fluctates temporarily from bad workings of the potentiometer. And hey, if I spring for a sensor and it turns out not to be the problem then at least 50% of the price has been subsidized by you

 

[suprarx7nut]

Huh, didn't think about the utility of BI1 in that way - a lot of the signals that end up at the AHC ECU go through there. Including the rear height sensor, but unfortunately or fortunately, not the front height sensors.

NO current codes or other symptoms, aside from, I suspect, a rougher ride than the AHC usually provides over smaller bumps.

I WANT to believe that this is as simple as changing out the sensors, but I'm skeptical, mainly because it SEEMS like the sensors read very accurately - they report the height that the truck stops at dead-on each time. Since height is voltage and voltage is height w/r/t the sensors, if the problem was one prematurely reporting that it had reached N voltage, then wouldn't it show a height of 0 mm? Because currently, they all show some negative number that matches the height that the truck lost between setting it up via active test and then going through a N>LO>N cycle.

I mean, I'm aware there's a lot of speculation when it comes to the esoteric workings of the AHC. And maybe it's much less predictable what happens if the voltage fluctates temporarily from bad workings of the potentiometer. And hey, if I spring for a sensor and it turns out not to be the problem then at least 50% of the price has been subsidized by you

The sensors are sampling often. I don't recall what it is on the 100, but it's multiple times per second. Techstream updates every 10 seconds or something extremely slow, but there's hundreds if not thousands of measurements occurring between the Techstream updates. The see the last one as Techstream updates. You do not see the other 4000 or whatever the sample rate and display time period is.

I'm sure the sensor is eventually settling on mostly the right number for you. If it's reporting the right number 95% of the time that's a complete and total failure, IMO. It'll look ok on Techstream, 19 out of 20 times, but it probably won't function correctly in use. It needs to be 99.9X% correct.

As it raises, if it gets a series of near 0mm results it will stop raising and consider that cycle complete. It should re-adjust after a few minutes, but I don't think it takes many poor readings to fool it.

Did you have a code previously?

 

[usedname]

The sensors are sampling often. I don't recall what it is on the 100, but it's multiple times per second. Techstream updates every 10 seconds or something extremely slow, but there's hundreds if not thousands of measurements occurring between the Techstream updates. The see the last one as Techstream updates. You do not see the other 4000 or whatever the sample rate and display time period is.

I'm sure the sensor is eventually settling on mostly the right number for you. If it's reporting the right number 95% of the time that's a complete and total failure, IMO. It'll look ok on Techstream, 19 out of 20 times, but it probably won't function correctly in use. It needs to be 99.9X% correct.

As it raises, if it gets a series of near 0mm results it will stop raising and consider that cycle complete. It should re-adjust after a few minutes, but I don't think it takes many poor readings to fool it.

Did you have a code previously?

I had a code after I first bought the car which was.. one month ago (seems like longer). The AHC was working then too but it threw a c1762 that I think was related to air in the pump - the reservoir was real low. I bled the system and cleared the code and it never came back.

I hope you're right about the sensor, and because I want it to be the answer I went ahead and ordered a FL sensor (which was the one one which I had to manipulate the brushes).

 

[suprarx7nut]

I had a code after I first bought the car which was.. one month ago (seems like longer). The AHC was working then too but it threw a c1762 that I think was related to air in the pump - the reservoir was real low. I bled the system and cleared the code and it never came back.

I hope you're right about the sensor, and because I want it to be the answer I went ahead and ordered a FL sensor (which was the one one which I had to manipulate the brushes).

If it doesn't resolve it, let me know. I'll have a key fob kit with your name on it.

 

[usedname]

If it doesn't resolve it, let me know. I'll have a key fob kit with your name on it.

And if you're right then I'll buy one!

 

[suprarx7nut]

And if you're right then I'll buy one!

Ha, perfect.

 

[IndroCruise]

Huh, didn't think about the utility of BI1 in that way - a lot of the signals that end up at the AHC ECU go through there. Including the rear height sensor, but unfortunately or fortunately, not the front height sensors.

NO current codes or other symptoms, aside from, I suspect, a rougher ride than the AHC usually provides over smaller bumps.

I WANT to believe that this is as simple as changing out the sensors, but I'm skeptical, mainly because it SEEMS like the sensors read very accurately - they report the height that the truck stops at dead-on each time. Since height is voltage and voltage is height w/r/t the sensors, if the problem was one prematurely reporting that it had reached N voltage, then wouldn't it show a height of 0 mm? Because currently, they all show some negative number that matches the height that the truck lost between setting it up via active test and then going through a N>LO>N cycle.

I mean, I'm aware there's a lot of speculation when it comes to the esoteric workings of the AHC. And maybe it's much less predictable what happens if the voltage fluctates temporarily from bad workings of the potentiometer. And hey, if I spring for a sensor and it turns out not to be the problem then at least 50% of the price has been subsidized by you

Mmmmmm -- I think I would suggest that all three Height Control Sensor circuits can be accessed via BI1 albeit the pathway passes via various other connectors along the way -- unless I am misreading the attached 2006 LC100 two-page EWD for AHC.

I do have to agree that a coloured version of the EWD would be a great deal easier!! As far as I know, AHC/TEMS wiring is common to both LX470 and LC100 (where AHC/TEMS is fitted) -- but just to be sure, if ever required, it would best to hang out for the appropriate LX470 EWD for your model year and/or meanwhile see whether @suprarx7nut or others might be willing to scan the appropriate EWD pages.

As you know, I started out pointing to the Sensors themselves -- especially the Rear Sensor which seemed most wayward to me -- but accepted your testing of all three Sensors per the FSM battery method -- particularly given that I had myself replaced all three Sensors with new OEM parts on my vehicle but without good effect, when faced with a similar problem.

In any case, for a vehicle of 17 years of age and service, replacing the Sensors certainly is in your future even if they are working now. They are 'wear items'. Obviously, deferring expense until really necessary is a good idea -- but @suprarx7nut is persuasive as always, and replacement is not going to be a waste of money if it is your plan to keep this relatively young vehicle, 2006 LX470 with a very low ~130,000 (?) miles, and retain AHC/TEMS.

Anyway, 'due diligence' has been done and a decision has been made -- hope all goes well!!

 

[usedname]

Mmmmmm -- I think I would suggest that all three Height Control Sensor circuits can be accessed via BI1 albeit the conductor passes via various other connectors along the way -- unless I am misreading the attached 2006 LC100 two-page EWD for AHC.

I do have to agree that a coloured version of the EWD would be a great deal easier!! As far as I know, AHC/TEMS wiring is common to both LX470 and LC100 (where AHC/TEMS is fitted) -- but just to be sure, if ever required, it would best to hang out for the appropriate LX470 EWD for your model year and/or meanwhile see whether @suprarx7nut or others might be willing to scan the appropriate EWD pages.

As you know, I started out pointing to the Sensors themselves -- especially the Rear Sensor which seemed most wayward to me -- but accepted your testing of all three Sensors per the FSM battery method -- particularly given that I had myself replaced all three Sensors with new OEM parts on my vehicle but without good effect, when faced with a similar problem.

In any case, for a vehicle of 17 years of age and service, replacing the Sensors certainly is in your future even if they are working now. They are 'wear items'. Obviously, deferring expense until really necessary is a good idea -- but @suprarx7nut is persuasive as always, and replacement is not going to be a waste of money if it is your plan to keep this relatively young vehicle, 2006 LX470 with a very low ~130,000 (?) miles, and retain AHC/TEMS.

Anyway, 'due diligence' has been done and a decision has been made -- hope all goes well!!

Hah I don't know if it's due diligence or wishful thinking on my part. Stepping back it looks like you as well as a couple other forum experts have said to throw a new sensor at it, and perhaps I should have listened sooner! Will update once I have more data or a fully functional system.

Edit: I'm using that same EWD and I don't see where the front sensors go through BI1/2. They connect to the ECU pins SHFL and SHFR, and their only other connections are to junction box 5 (for SHB which I think is power?), and ground (also through JB5).

 

[usedname]

Well, new FL sensor didn't make any difference. Also I now have 5 trouble codes, but techstream keeps on popping up an error when I try to look them up.

The error code (0x91020324) hasn't been solved by anyone online, far as I can tell.

I checked if 'F/R wheel steps' changes as I'm riding around, and it does. The numbers are highly variable as I drive, and seem to be affected by the damping mode. I assume this is normal.

Also of note, when in Active Test mode, I couldn't get the car to rise or fall in Comfort mode, but I could in Comfort+ and Sport+. The buttons did different things in each mode. I thought perhaps that means there is something wrong with the damping mode switch, but in Techstream the 'Damping Force Switch 1/2' both change appropriately according to the four modes.

Everything is still working. Car just refuses to go back to the right height. Rear is still -13mm.

Throw more sensors at it? Or time to man up and check some wires?



EDIT: Reinstalled Techstream but I still get the same error, but I found the procedure, connecting TC to CG pins in the DLC3.

Here are my brand spankin new codes:

C1731	Front Damping Force Control Actuator RH Circuit Malfunction
C1732	Front Damping Force Control Actuator LH Circuit Malfunction
C1733	Rear Damping Force Control Actuator RH Circuit Malfunction
C1734	Rear Damping Force Control Actuator LH Circuit Malfunction
C1736	Front Suspension Control Valve RH Malfunction

I don't think these are active codes, I suspect I might have turned the car on when I had BI1/BI2 disconnected. So this was a red herring, as far as I'm concerned.

 

[TreatSmash]

WOW, must be rusted to the frame!

I finally got the 4th globe on today.

You gave me a clue when you said 2 bolts and 1 nut holding the whole assembly to the frame. I found the second bolt on top of the frame UNDER the exhaust shield.

Well I got the assembly off, put the globe in a bench vice and used a giant pipe wrench on it. Man it was on there!

Now it's all put back together and bled. I'm getting like 17 graduations. My heights are off but I'll work on it tomorrow.

 

[usedname]

Also I offer up a color AHC wiring diagram as blood sacrifice.