AHC Off Flashing. C1711 + C1776

Joined
Feb 22, 2011
Messages
27
Hi guys,

I took the Cruiser out for the first drive this year. It parked 4 month in a clean and dry barn. (Batteries have been on a charger once a week.)

The Cruiser fired up fine. Unfortunately the AHC „OFF“ started flashing. Ride quality is fine. AHC is in neutral position. Everything works like always. Only the flashing „off“ and I can‘t go in High.

I‘m getting the codes C1711 and C1776.

I had a new height sensor (cheap one from ebay) anyway. So I put that one on the front passenger side. Also checked the connections. Unfortunately it did not fix the codes and problem!

Put apart the old sensor. Still looks like new from the inside. See attached.

Any idea what to do next?

It is a European diesel HDJ 100 from end of 2002.

EB1A19BA-51B9-45F8-A87C-F463ADF8019C.jpeg
 

LndXrsr

AHC Aficionado
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Cincinnati
C1711 is front right sensor as you're troubleshooting. Often, cheap sensors don't fix the issue. OEM or Aisin full sensor/arm units are the most reliable way to replace.

C1776 is a wheel speed sensor issues it seems. May be related and resolve with a new height sensor in place per some reports I've seen, but also can pop up if the battery voltage is low (bad alternator or dying battery). May also be the wheel speed sensor itself, unfortunately.


I'd try a better quality front right AHC height sensor as your next move.
 
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Strongly agree with @LndXrsr .

By the way, the picture in Post #1 in this thread provides a close-up of only half of the Sensor. Of equal importance is the other half -- the "lid" which has the the carbon track on the inside surface and on which the tiny brushes run. Together these parts make up the Sensor which is a simple potentiometer (also called a voltage divider) based on an invention by Thomas Edison way back in 1875 -- no fancy modern electronics inside this gadget in a LC100 or LX470!

The Sensor works by providing a voltage signal to the ECU corresponding to the vertical wheel position relative to the chassis. If the ECU receives a persistent signal outside the FSM-prescribed range of 0.3 volts to 4.7 volts, the ECU records a DTC and places some or all of the AHC/TEMS systems in 'fail safe mode' to protect the system, the vehicle and the driver from uncontrolled suspension behaviour.

Suggest also be aware that the absence of a DTC does NOT assure that a Height Control Sensor is good. It can easily happen that an old or damaged or poorly manufactured Sensor transmits a wrong voltage signal for the height of the vehicle but within the above voltage range acceptable to the ECU -- in which case no DTC appears, but it is still a dud Sensor, recognisable from errant behaviour of the vehicle. In the case of this vehicle, the absence of DTC C1712 (Front Left Sensor) and DTC C1713 (Rear Sensor) does NOT tell you that these Sensors are good.

It is a mug's game trying to determine Sensor condition by eye. There can be unseen and unseeable imperfections or inconsistencies in the condition or thickness and/or conductivity of the carbon track, depending on wear and tear as well as ìnconsistent manufacturing quality in the first place (which is why OEM Toyota/Lexus or Aisin replacements are recommended). The FSM-prescribed electrical test (volts) of the Sensor is best, second best is to check the resistance (ohms) of the Sensor though its full swing angle (about 90 degrees), looking to see that the resistance changes in a smooth linear manner, no jerks or continuity interruptions or other scratchy behaviour.

AHC - Height Control Sensor - explanation of deterioration 2.jpg


In addition to the Sensor itself, it is important to examine the condition and continuity of the connector at the Sensor AND ALSO the short piece of harness which runs up to a connector on top the RHS wheel arch (in the case of C1711), as well as this connector itself. Poor or lacking continuity in these parts will interfere with the signal to the ECU and will result in the same DTC. The same can be said of the harness all the way back to the ECU -- but this is less likely.

Suggest read all about Sensors and how they work (and an illustrated description of how the whole AHC/TEMS systems work) at:
then use tabs on LHS of opening page
New Car Features > CHASSIS > Suspension > Active Height Control Suspension and Skyhook TEMS

Tnen suggest read all about Height Control Sensor DTC Conditions (or 'rules') and Sensor 'fail safe functions' and testing at:
then use tabs on LHS of opening page
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS > C1711 to C1713 (while there, suggest scroll down to C1776 re speed sensors)

Height Control Sensors can be very long lived (unless rust-affected or corroded due to water ingress) -- but ultimately they are 'wear items'. After a long life of 22 years, if one Sensor has failed, failure of the others may be in your future:

Toyota/Lexus Height Control Sensors – Part Numbers:
89405-60012 (Front Right)
89406-60022 (Front Left)
89407-60010 (Rear)

Aisin Height Control Sensors – Part Numbers:
HST-020 (Front Right)
HST-021 (Front Left)
HST-026 (Rear)

It is a good idea to pre-test ANY Sensor (new or used) before installation.

On the Wheel Speed Sensor, suggest be aware that the harnesses from the RHS Front Speed Sensor and the RHS Front Height Control Sensor rise to connectors next to each other on the top side of the RHS Front Wheel Arch. The Height Control Sensor has three wires. The Speed Control Sensor has two wires. It is a good idea to check that connectors are tight. This also can be a good place to do some basic tests (after opening these connectors).

The pic below shows the Height Control Sensor harness connector and the adjacent Wheel Speed harness connector in the red ring. The AHC Pump has been removed, its connectors are shown in the green ring.

AHC Connectors Question.jpg
 
Last edited:
Joined
Feb 22, 2011
Messages
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@IndroCruise wow!!! That‘s very good information. Thank you!!!

I do not have Techstream though I ordered a cable today. What I have is the App ELMscan on an old phone as it only runs on Android. I checked the height sensors and got confusing readings. Any thoughts on that?

Front right 183mm
Front left -14.8mm
Rear 1.0mm

Cruiser is quite leveled out.

I had a little sensor lift done a couple of years ago.

I just ordered an Aisin right height sensor. Thanks for the part number. $50 cheaper than a Toyota one.

Is the one on the left also not reading correctly ?

EA088E1B-62C4-456B-A62A-4B6919FAD7D7.jpeg
 
Joined
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Rodents perhaps!

Having both RH wheel speed sensor and RH height sensor. Kicking out DTC at same time. After sitting in a bran. I'd inspect very closely for rodent damages. They love nesting where there's food (WIRE sheathing).
 
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@IndroCruise wow!!! That‘s very good information. Thank you!!!

I do not have Techstream though I ordered a cable today. What I have is the App ELMscan on an old phone as it only runs on Android. I checked the height sensors and got confusing readings. Any thoughts on that?

Front right 183mm
Front left -14.8mm
Rear 1.0mm

Cruiser is quite leveled out.

I had a little sensor lift done a couple of years ago.

I just ordered an Aisin right height sensor. Thanks for the part number. $50 cheaper than a Toyota one.

Is the one on the left also not reading correctly ?

View attachment 2991599

I use ELMscan as well on my HDJ100 for AHC settings and adjustments -- which is all I want. Very convenient, easy plug-and-play connection (after the settings are sorted out), Bluetooth connection, easy to use around or under the vehicle and I can see all of the full suite of AHC information I want to see, sensors, pressures, do some graphs, etc, etc.

In my case, it works with a simple and cheap dongle called “ELM327 Mini Interface” – widely available on Amazon and eBay for around USD11.00. This plugs into the DLC3 port under the dashboard.

I use this with
ELMScan Toyota - Apps on Google Play - https://play.google.com/store/apps/details?id=com.obd2.elmscantoyota (Cost: around USD6.00 if I remember correctly).

While very convenient (especially when travelling), there is much wider functionality on Techstream, so may I suggest that you persist with acquiring Techstream and setting that up if you can.

Back to the case, in which the following Height Control Sensor readings are reported:

Front right 183mm
Front left -14.8mm
Rear 1.0mm

These should be “close to zero” at “N” height setting. "Close" means +/- 5mm in metric.

First step: Confirm that the Front of the vehicle has been ‘cross-levelled’ – meaning that hub-to-fender distances Front Left and Front Right are equal. If not, use torsion bar adjusters to achieve this – see attachment.

As you may know, the Front Height Control Sensor adjusters cannot be used for cross-levelling. This is hydraulically impossible. When the vehicle is stationary (or moving with Front wheels straight ahead), the Front Left and Front Right sides are connected via the open Front Gate Valve within in the Control Valve Assembly. This means that Right and Left Front AHC pressures are equalised. Moving one Height Control Sensor adjuster may change the overall Front vehicle hub-to-fender height and therefore also change the Front AHC pressure but the Left and Right AHC pressures equalise, so there cannot be any side-to-side hub-to-fender change from this action. Ditto at the Rear of the vehicle. The AHC system in LC100 and LX470 is a two-channel system -- it can raise or lower the Front and Rear of the vehicle -- it cannot raise or lower each wheel individually. The Front and Rear Gate Valves only close when directed by the ECU if the vehicle is cornering at speed, to increase roll resistance.

Second step: Check Height Control Sensor readings again.

Assume 183 mm on RHS Front Height Control Sensor (or some other big number) remains after cross-levelling? If so, then this reading (equivalent to 7.2 inches) is so ridiculously large that it could never be fixed at the Sensor adjusters. It really is confirming that there is a problem with this Sensor – best to replace it as planned with a Toyota/Lexus or Aisin item.

Suggest now look at the LHS Front Height Control Sensor while it is still on the vehicle with the vehicle at “N” height, front wheels straight ahead, wheels on ground or on the pads of a hoist (but not hanging free), with Ignition Switch “ON”, ELMscan connected and awake and showing Height Control Sensor readings, but engine NOT STARTED. Do not want the suspension to move while doing Sensor adjustments – dangerous and also inaccurate.

If possible, see if you can use the sliding adjuster (see pic below) to move the LHS Front Height Control Sensor until it reads as close as possible to zero on ELMscan. (You can use the ‘heim’ threaded bolt but this is very fiddly). This where you may need a hoist (weight of vehicle must be on the wheels) or maybe put the vehicle on a ramp so that you can reach around the tyre to the Height Control Sensor adjuster.

If you cannot achieve a “close to zero” reading then it is possible, even likely, that this LHS Front Sensor also is faulty – suggest remove it, test, and replace with a new Sensor if necessary.

Fit the new Front Height Control Sensors and adjust if necessary as above. If you have bought a new Sensor with linkage attached, it is likely that when taken out of the package the linkage is held in place at the mid-swing position with a temporary plastic pin (see last pic below). This is the factory setting of the Sensor at “N” vehicle height. When installing, you can move the adjuster to accept this position without breaking the temporary pin. Then you should have the Sensor reading close to zero millimetres. It is no problem if you have chosen some other hub-to-fender height at “N” height position – for example, if a “Sensor lift” has been done. In this case, again just move the adjuster until close to zero is achieved on ELMscan, even if this breaks the temporary plastic pin. The temporary plastic pin is there for convenience – it is not essential.

The important point is that the mid-swing position is the position to which the ECU will cause the vehicle to return when "N" vehicle height is selected at the console switch and when the vehicle is self-levelling.

There are two vital references to follow to complete the correct adjustment of the AHC suspension:

The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/#post-13116520 – information assembled by @LndXrsr

AHC Info - https://www.yotamd.com/blogs/news/ahc-info video produced by @suprarx7nut

Hopefully, the Rear Height Control Sensor is OK. (See note by @2001LC concerning possible harness damage anywhere, caused by rodents!)

For more information on correct AHC settings, see

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


AHC Front Height Control Sensors.jpg


This Rear Sensor in the next pic was bought as Toyota/Lexus Part Number from Partsouq -- but stamped "AISIN". This no surprise -- AISIN is a major supplier to Toyota/Lexus --and Toyota is a significant investor in AISIN!! Direct purchase from AISIN may be cheaper.
AHC Rear Height Control Sensor.jpg


AHC - RHS Front Height Control Sensor with N pin.jpg
 

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Last edited:
Joined
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Thank you @IndroCruise Again some very good, useful and helpful information!!!

I was away on work but will check everything out this weekend.

The car should be cross-level as I did the torsion bar adjustment last year. But I will check again.

Today I received the right side Sensor. But unfortunately something is broken off. Is this thing necessary? The sensor was shipped from the US to Germany as it was way less expensive… I could return it but that will take some days again. Moreover I have to wait again to get a new one. Opinions?

7978F970-81DE-460B-BA21-409718A3185F.jpeg
 
Joined
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Thank you @IndroCruise Again some very good, useful and helpful information!!!

I was away on work but will check everything out this weekend.

The car should be cross-level as I did the torsion bar adjustment last year. But I will check again.

Today I received the right side Sensor. But unfortunately something is broken off. Is this thing necessary? The sensor was shipped from the US to Germany as it was way less expensive… I could return it but that will take some days again. Moreover I have to wait again to get a new one. Opinions?

View attachment 2994643

Nothing to worry about. Personally, I would not bother to return the Sensor for this cause.

Your picture shows the tiny slider and temporary plastic post used by the manufacturer (such as AISIN or TOYOTA - maybe "TOYOTA" is the word just visible behind the Sensor arm? ) to set the mid-point of the swing of the Sensor arm to give a signal of ~2.25 volts, corresponding to the "N" height setting.

Why does this exist? As can be imagined when looking at the picture of the "track" inside the Sensor cover in Post #4, there is likely to be some variation in manufacturing of this "track". One Sensor can be slightly different from another. This arrangement allows the Sensor manufacturer to test and position the Sensor arm at the correct voltage (or resistance) for "N" height at or very close to mid-swing. As a matter of interest, you could measure this voltage using the FSM Sensor test procedure before installing the Sensor.

The arrangement aids installation, particularly on a production line. As mentioned in Post #7 and picture in that Post, this may be of assistance when installing a replacement Sensor.

However, it is necessary in any case to check and adjust the new Sensor (and the other Sensors) on the vehicle at your preferred "N" height using the sliding adjuster or the double-ended 'heim' threaded adjuster, also shown in a picture at Post #7. This adjustment is the main thing -- the temporary plastic post etc is explained above because questions do arise but it is a nicety which most people can ignore.

You will not see Height Control Sensor voltages or resistance on Techstream. Instead, the ECU and/or Techstream translates these to millimetres or inches. When installed on the vehicle, the aim is to adjust the Sensors to read as close as possible to zero millimetres (or zero inches) on Techstream when the vehicle is at your preferred "N" height, wheels on a level surface, and wheels straight ahead, Techstream connected, ignition "ON", but engine "OFF", not started, (otherwise the AHC system will cause the vehicle to move during adjustment -- dangerous).

When the Sensor is installed and operating on the vehicle the temporary plastic post described in my Post #7 will break and become redundant and of no further use.

If you are concerned about the Sensor, before installation you could remove the screw holding the temporary plastic pin in place and test the Sensor through its full range of movement using the FSM test procedure given in my Post #4 in this thread, looking for a smooth change through the movement with no discontinuities.
 
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@IndroCruise I measured the cross level. It is almost the same left and right. Just about 0,5mm (0,02in?).

Then I put the new sensor in. Unfortunately I couldn‘t get the screw off from the sliding adjuster. So I kept the old arm. So far so good. (Need to get the wheel off as the screw has lots of rust)

I started the car, deleted all DTCs and drove around the next corner. The car started dropping the front all the way down. Though it still shows N. Also no DTCs in ELMScan.

BEFORE the car dropped down ELMScan showed the following numbers:

FR Sensor 113mm
FL Sensor -107mm
Rear 3mm

Can I assume the left sensor is dead? Should I try to put one of the others in and see what happens? I have the old genuine one from the right and the cheap new ebay one.

Or is the problem somewhere else?

3ED7A461-B4AF-48B1-8631-51287388CF09.jpeg


0150508C-287C-4FD8-8A9B-57C78A5B7778.jpeg
 
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I have to order the left sensor as well. Destroyed the sensor when trying the undo the screw. Now the screw in the sensor is turning...
 
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I have to order the left sensor as well. Destroyed the sensor when trying the undo the screw. Now the screw in the sensor is turning...

At Post #1:

C1711 – Right Front Height Control Sensor Circuit (not just the Sensor)

C1776 –Front Wheel Speed Sensor (probably related to the Height Control Sensor problem because the Sensor reading is very high, DTC possibly occurred when faulty Sensor wrongly indicated to ECU that the wheel is at “HI” height (or higher) at a prohibited speed -- see FSM extract below. If so, this will be rectified when the Sensor problem is rectified.

AHC Heights and Extra HI.jpg


At Post #5
:

Observed symptoms:

“I measured the cross level. It is almost the same left and right. Just about 0,5mm (0,02in?)”.

So cross-level measured by tape-measure is good!

Sensor readings:

Front right 183mm
Front left -14.8mm
Rear 1.0mm


Difference between Front Right and Front Left: 197.8 mm (7.87 inches). Not good! Huge difference! Neither the individual readings nor the difference between Sensors are “close to zero”. The Rear Sensor may be OK but this is not yet confirmed.

The Front Height Control Sensor readings contradict the tape-measured physical facts because the vehicle is cross-level, not leaning.

Conclusion: Combined with DTC C1711, the symptoms indicate a faulty Front Right Height Control Sensor circuit – meaning there is a fault in the Sensor or Connectors or Harness.

A New Front Right Height Control Sensor was purchased, including new connectors and short harness to the joining connector above Front Right wheel arch.

At Post #10:

Observed symptoms:

New Front Right Control Sensor (including connectors and harness but not the threaded arm) was fitted but Sensor was not adjusted due to rusted or stuck fittings.

Cleared DTC’s and no DTC’s returned after driving.

In operation, vehicle drops in physical height but AHC indicator at dashboard continues to show steady “N”

BEFORE the car dropped down ELMScan showed the following numbers:

FR Sensor 113mm
FL Sensor -107mm
Rear 3mm


Difference between Front Right and Front Left: 220 mm (8.66 inches). Again, not good! Huge difference! Neither the individual readings nor the difference between Sensors are “close to zero”. The Rear Sensor may be OK but this is not yet confirmed.

Again, the Sensor readings contradict the tape-measured physical facts because the vehicle is cross-level, not leaning.

The conclusion is unclear
because there was no opportunity to adjust the previously installed new Right Front Sensor nor the old Left Front Sensor to achieve “close to zero” readings at “N” height on both Front Sensors, as previously described.

As explained previously, absence of a Height Control Sensor DTC does NOT provide assurance that the Height Control Sensor is OK.

It is possible that the old Left Front Sensor circuit -- meaning Sensor or Connector or Harness – are faulty. In any case, the Left Front Sensor is now damaged and due for replacement.

When fitting the new Left Front Sensor, check that all upper and lower electrical connectors are good, check that the sliding adjuster is approximately in same position on Right and Left sides and also check that the threaded adjuster bolt is approximately the same length on the Right and Left sides.

As discussed previously, different Front Sensor positions DO NOT and CANNOT affect or cause the vehicle to lean.

However, widely different Right Sensor and Left Sensor readings caused by different arm positions (and therefore different electrical brush positions inside the Sensor) would cause different Right and Left signals being sent to the ECU. If the differences are large enough -- as in this case -- the ECU will be unable to resolve the error. Instead, the ECU will cause ‘fail safe function’ in which the ECU will prohibit operation of the AHC system until the Sensor error is resolved by adjustment or by installing new Sensors.

If the two Front Sensor circuits (meaning Sensors and Connectors and Harness) are healthy and installed with the sliding adjusters in approximately similar positions and the threaded adjuster set at approximately similar length, then ELMscan (or Techstream) should show approximately similar Height Control Sensor readings. It should then be possible to recover AHC operation (unless there also is a problem with the Rear Sensor circuit or some other fault in the AHC system).

After recovering AHC operation, then it is necessary to adjust the Height Control Sensors properly -- may need prior removal of rust and road grime from adjusters and treatment with penetrating fluid. Then:
  1. place console height selector in “N” position,
  2. then use “Active Test” procedure -- see attachment at Page 6 -- "Section 5 --Height Control Operation (Active Test)" -- to set vehicle at the desired height at Front and Rear,
  3. then exit “Active Test”, connect ELMscan, ignition “ON”, but engine “OFF”, not started,
  4. then adjust all Height Control Sensors so that reading on ELMscan is as “close to zero” as possible.
Other methods of adjustment are possible. For example, to give easier access to Front Height Control Sensor adjusters:
  1. Allow vehicle to settle at “N” height after driving,
  2. Check front cross-level again,
  3. Decide on preferred tape-measured hub-to-fender distance at “N” height setting -- 500mm or 19.75 inches at Front is usual – but other choices are possible to give some permanent lift (called ‘sensor lift’) at “N” but stay within limits of shock absorber travel, droop requirements and rake requirements,
  4. Secure the vehicle on a level surface,
  5. Place suitable jack carefully and securely under Front Lower Control Arm,
  6. For safety, place vehicle stand under chassis rail, positioned to catch vehicle in case of uncontrolled movement,
  7. Place second jack under chassis rail,
  8. Raise vehicle sufficiently using jack under Lower Control Arm to allow removal of wheel,
  9. Adjust jack under Lower Control Arm to achieve desired tape-measured hub-to-fender distance (to manipulate hub-to-fender distances, may need weight in vehicle or the second jack under chassis),
  10. Connect ELMscan (or Techstream), ignition “ON”, but engine “OFF”, not started,
  11. Adjust Height Control Sensor adjuster to achieve a reading as “close to zero” as possible on ELMscan (or Techstream) when hub-to-fender distance is correct,
  12. Replace wheel, remove jack, check Height Control Sensor reading,
  13. Repeat on other front wheel,
  14. Drive vehicle to allow suspension to settle,
  15. Check hub-to-fender tape-measurements and cross-level and check Height Control Sensor readings,
  16. Fine tune adjustments if necessary,
The AHC system causes the vehicle to self-level at "N" by the ECU causing the vehicle to raise (using AHC Pump) or lower (by opening Gate Valves in the Control Valve Assembly) until the correct signal for "N" height is received from each of the three Height Control Sensors. The ECU determines the heights when "LO" or "HI" height is selected at the console switch. Only the "N" height setting is used for adjustment purposes. Correct adjustment of healthy Height Control Sensors without conflicting signals nor major differences in readings is important to allow the AHC system to operate correctly.

Late edit:
For further information which may be helpful, see also the series of Posts at the link below, starting at Post #8 and onwards through to Post #18:

Intro and yet another AHC thread… - https://forum.ih8mud.com/threads/intro-and-yet-another-ahc-thread.1281317/#post-14390564
 

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Your knowledge is amazing @IndroCruise Thank you so much.

I did connect the new FL Sensor.

I also did check the new FR Sensor again. I was to stupid and did not connect the sensor arm correctly. Now it is fine.

Readings are:
FR -63mm
FL -84mm
RR -46mm

In my opinion this is correct.
Car is in low.
FL Sensor arm needs little adjustment. That will gain the 20mm.
Rear has King Springs and Spacer. Cant go lower

I tried the active test and it FAILED. It did not work. Some interesting thing I noticed. Maybe helpful for others which are as dumb as me. If you connect OBD at the same time, like my ELMscan dongle. You can not do the active test! I disconnected the dingle and I was able to start the active test.

I hear the pump working. But the car won’t move up or down.

After the active test I started the car again. Tried to go to N. The pump is „making a noice“ but nothing happens.

But I got a new code: C1762

Does that make any sense?

EDFAD9A2-EF6F-418D-9D3A-D90E9DBA69BB.jpeg
 
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Is it plausible that I first have DTC C1711 and C1776 and after fixing those I get C1762? Or do you thing there is still something going on with the sensors?
 
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Is it plausible that I first have DTC C1711 and C1776 and after fixing those I get C1762? Or do you thing there is still something going on with the sensors?

Probably you already know this, but just to be sure, all AHC testing and measurements on ELMscan or Techstream must be done with all doors and rear hatch closed – AHC system is designed not work if the ECU detects that any of these are open (or with a problem in the door switch circuits). The engine hood can be left open. AHC pressure readings need to be done after moving heights “N” to “LO” to “N”, waiting for the green dashboard light to stop blinking then wait for a further 30 to 60 seconds with engine running before taking readings. This ensures that the raise is complete AND that the AHC Pump has had time to re-charge the Height Control Accumulator and the Pump has stopped. Personally, I have to ‘re-learn’ these lessons most times I do these tests -- such is my impatience!!

As explained in Post #12, C1711 and C1776 are consistent with the then problematic Right Front Height Control Sensor Circuit (not just the Sensor itself).

Also as explained in Post #4, absence of DTC does NOT provide assurance that a Height Control Sensor is OK and working correctly. The Sensor can be faulty with wrong outputs for the vehicle height but there will be no DTC if this wrong signal remains within the range accepted by the ECU.

C1711toC1713.jpg


Both the Right Front and Left Front Height Control Sensor have now been replaced with new OEM Toyota/Aisin Sensors complete with new harness segment which joins the main AHC harness at a connector above the respective Front Left and Front Right wheel arches.

Unless there is harness damage around those connectors, it seems reasonable to assume these two new Front Sensors and circuits are in good shape. Suggest assume OK for now. To be sure, you would need a check that the connectors right back at the Electronic Control Unit (AHC) are tight and use a multimeter to check that the voltages in the circuit are correct at the ECU -- see FSM-DIAGNOSTICS section at Page DI-218 – “Terminals of ECU”.

The jury is still out on the Rear Height Control Sensor. The condition of this Sensor is not known. Given that the Rear Sensor is the same age as the Front Sensors, it is worth testing this Sensor per FSM, for confidence that it is working correctly and reliably.

Reported observations are:

FR -63mm
FL -84mm
RR -46mm

In my @HDJ80fan opinion this is correct.

Car is in low.

FL Sensor arm needs little adjustment. That will gain the 20mm.
Rear has King Springs and Spacer. Cant go lower.

Front AHC Pressure: 1.7 MPa
Rear AHC Pressure: 3.3 MPa
Height Control Accumulator Pressure: 0.0 Mpa


The Height Control Sensor readings in ELMscan suggest that either (1) the vehicle may be on the front bump stops, or, (2) all three Sensors are out of adjustment – meaning, not reading “close to zero” at “N” height (probably because it has not been possible get the vehicle to raise to “N”?)

By the way, it is always very helpful to diagnosis when quoting Height Sensor readings also to record and quote the tape-measured hub-to-fender distances on all four wheels at the same time.

Some differences between the Height Control Sensor readings are large: FL to FR is 21 mm (almost three-quarters of an inch), FR to RR is 17 mm, FL to RR is 38 mm.

The FSM is unclear how much difference is enough to put the AHC system into ‘fail safe function’ – but I would be suspicious about the FL to FR difference. Conflicting height sensor signals mean that the ECU cannot resolve the correct vehicle height to match the height selection switch on the console – and instead adopts the ‘fail safe function’.

The Front to Rear differences in height sensor readings are very large. It possible that there is a Rear sensor problem. However, the AHC system on LC100/LX470 is two-channel (Front and Rear) system in which Front and Rear are largely independent, so a Rear sensor problem would not be my first assumption, unless the Rear Sensor reading obviously is inconsistent with the Rear tape-measured hub-to-fender distances.

I don’t think the KING KTRS-79 springs have much to do with it. I have those same springs (but not spacers) and I still get close to the actual physical FSM-specified height changes “LO” to “N” to “HI” within about 5 mm (tape-measured hub-to-fender). You must be carrying an enormous Rear load if both KING KTRS-79 springs AND spacers are required? This combination will result in very low AHC pressures and poor damping performance (more 'springy' ride) when the vehicle is empty or does not have much permanent Rear weight for example Rear bar, drawers etc.

As shown in your ELMscan readout, the required Front and Rear AHC pressures and the Height Accumulator are not building up -- which is why the vehicle is not raising.

Suggest read up on what C1762 means and the specified conditions which give rise to this DTC:

then use tabs on LHS of opening page
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS > C1762

C1762.jpg


In response to your last question, it can happen that the ECU displays a DTC for the first problem that it discovers, then when that is fixed, the ECU reveals the next problem it finds in the sequence. Suggest that this method of revelation not be allowed to become a distraction -- just "go with the flow".

Are any other pump-related DTC's showing -- particularly DTC1718, DTC1741, DTC1751?
(In any case, suggest read up on these to get a better understanding of the system -- see same DIAGNOSTIC section of the FSM as referenced previously -- and in particular, note in each case the slightly different 'fail safe functions' which become important symptoms to observe, with or without DTC's).

It is mentioned that the AHC Pump can be heard working "but nothing happens other than noise".

So more information is necessary to start to figure out what that means and why movement is not happening.

Can you please advise for how long the AHC Pump is working before it stops?

Has there been any work on the AHC system (including any bleeding of AHC Fluid) which might have allowed air to enter the system?

When was the AHC Fluid last changed?

What are the hub-to-fender heights at each of the four wheel positions?

How old are the 'globes' on the vehicle?
 
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Feb 22, 2011
Messages
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Hey @IndroCruise again Thank you!!!

I was the weekend not at home and just returned. I suppose front is on bump stops. See pic.

Tape measures are:
FL 42,5mm
FR 42,5 mm
RL 48mm
RR 49mm

Before I put the first new sensor in the car was still in N. Tape measures have been:

FL 53,5mm
FR 54,5mm
RL 53mm
RR 54mm

Though the AHC system already was in „Off“ so I don‘t know if those are the „real“ N measures like the years before.

I do not have other DTCs at the moment. Only C1762. I deleted the DTC and the pump is running for about 20 seconds!? Good? Bad? Then DTC shows again.

No work on AHC for 3 years. Last fluid bleed was 20.000km about 12.500miles ago. Always enough fluid in reservoir.

Globes assumed to be the first ones. 310.000km about 192.000 miles old.

I ordered a new rear sensor.

Also build a cable to check voltage. Hope it makes sense to check the as is car voltage and not the battery test with 3x 1.5 batteries.

I only had time to check FL sensor. It showed 1,2v! Isn‘t that to much?
About the weight. I run a iKamper RTT, awning, fridge and drawers in the back. With the family we are around 3,4t. Someone on ih8mud recommended King springs and spacers. Never had issues with AHC pressure. Checked that all the time.

Thanks again!!!

9A434C31-609D-4ED0-83B2-30D36E19EFDA.jpeg


C1FB2167-AA6C-46C2-9FA3-2BBF001F6DE3.jpeg


48F5B13E-F878-46D1-95FC-4C9D42845165.jpeg
 
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Feb 22, 2011
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Adjusted the sensors. They are all around -70mm now when on low.

Car is still not going up. Still C1762
 
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Feb 22, 2011
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Unfortunately I wasn‘t able to fix the AHC. We had holiday planed and time was ticking. So I took the decision to have the AHC replaced. One day before we left on holiday the mechanic did his work and I have OME now installed. Long story short: Happy to go on holiday but the smooth AHC ride ist gone…

4295B946-94DB-45EA-A25A-8C0C66CAA536.jpeg
 
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? for anyone:

Would running the pump motor, via a jumper from 12 volt battery. Raise the vehicle from L, when flashing off (in fail safe mode) while OG key OFF?
 

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