AHC C1762 (2 Viewers)

[IndroCruise]

Wow, that's so much info. Thanks again for taking this effort to help me out.

I've attached the techstream results. They were on a flat as I could find surface so clearly they are miles out.


1. Error codes remain unchanged.
2. Note that I have previously flushed ahc with new fluid
3.
At that point, the ECU initiates ‘fail safe function’ defined for C1751 -- meaning that

• height control is prohibited, and,
• the AHC Pump stops and will not raise the vehicle, and,
• the vehicle adopts the height of the lowest wheel according to the signals sent by the Height Control Sensors to the ECU -- to do this the ECU opens the Front and Rear Levelling Valves in the Control Valve Assembly, allowing AHC Fluid to escape back to the AHC Tank, and so the vehicle settles.

That seems to describe the symptoms on your vehicle?


The scenario you described DOES sound like what's happening.

I'm juggling 2 little kids and having to have a go at this bit by bit so excuse me if I can't get all the info for you immediately.

Gotta run but I'll have another read later

Cheers

View attachment 3292180

Thank you for the Techstream screenshot. Other than the Height Control Sensor readings and the non-operation of the AHC system, there is nothing too alarming here. Voltages are a bit low -- need to watch these, Steering Angle is OK, Fluid Temperature is OK, Door Switch is OFF - OK, Brake Light Switch is OFF - OK, Main Relay Expectation is ON - OK, Ts and Tc are OFF - will think about these overnight, other switches and settings look OK.

When you can ....

• please confirm which are the two DTC's showing on Techstream,
• please advise whether the vehicle is resting on any of the bump stops when at your level place, and also,
• please measure and advise the hub-to-fender heights at all four wheels at the same place,

..... all corresponding to the Techstream screenshot showing the Front and Rear Height Control Sensor readings at the same location.

Measurements are a bit unreliable at anything other than N height because there can be some variations in the way the vehicle moves and some effects if the Front end alignment is out and/or if there is damage at the Rear end -- but at the moment, with AHC not working, there is no choice but to measure the vehicle in its current condition at the most level location you can find.

The idea here is to understand of how much of the Sensor difference might be due to a physical 'lean'? Is the vehicle actually low by a lot by tape-measure at the Front Right??? This also would usually mean that the diagonally opposite Rear Left is high (but depends a bit on any history of wear and tear and/or damage to chassis or body or mechanical suspension components, tyre type, pressures and wear being similar) -- but please tape-measure at all four wheels anyway.

If the Sensor readings are not accounted for by a physical 'lean' of the vehicle, then one or all of the Sensors (or circuits) are suspect -- mal-adjusted or faulty -- assuming that the Front end geometry and Rear end geometry is in reasonable shape, meaning no components, nor chassis, nor body are measurably damaged.

At N height, unless the vehicle has been 'lifted', for example using Sensor adjustments, and if it is basically in 'stock' condition, then around 19.75 inches (500 millimetres) hub-to-fender both sides at the Front would be good (if 19.50 inches also is OK) and 20.50 inches (520 millimetres) hub-to-fender both sides at the Rear also would be good.

If stuck at LO (not on bump stops) then would expect around 50 millimetres less at the Front, around 40 millimetres less at the Rear -- regard these numbers as guides, not measuring to the millimetre here:

If there is a 'lean', it is worth trying to correct this with the torsion bar adjusters, (engine OFF, do not want AHC system to suddenly 'wake up'), needs a good squirt of some kind of thread penetrating fluid on the adjuster threads the day before, then needs a 30 millimetre socket, a strong arm and possibly an extension bar or pipe of some kind, then see yet another attachment below labelled "AHC cross level per FSM".

In this step you are just trying to equalise Front Left and Front Right physical hub-to-fender tape measurements -- and if a tape-measure is available just use string or a marked stick -- don't worry about actual 'ride height' measurement numbers too much until AHC is working again -- because it is the AHC system and the Height Control Sensor adjusters which will be used to set 'ride height' eventually, not the torsion bar adjusters on an AHC-equipped vehicle.

So after Front 'cross-levelling', measure and record hub-to-fender at all four wheels again. Read and record Front Height Control Sensor reading and Rear Height Control Sensor again. (Note that height control is only Front and Rear on LC100/LX470 -- height at each wheel is not individually controlled by the AHC system on LC100/LX470).

Re-start engine. Re-start AHC system by pushing down ON/OFF switch for ~10 seconds, all doors and rear hatch closed, vehicle in PARK, foot OFF brake.

If you get a lucky break, this might be enough -- but I really think that there will be more to do.

Anyway, enough for today. Please consider -- and when you can, please provide an update with data as requested above -- and a path forward then can be discussed ......

By the way, if you can recall, please also advise what the AHC pressures may have been when the AHC system was last operational. Also suggest look for signs of AHC Fluid weeping at the 'shock absorbers' -- this may indicate a history of excessive AHC pressures.

 

[Skruf]

Thank you for the Techstream screenshot. Other than the Height Control Sensor readings and the non-operation of the AHC system, there is nothing too alarming here. Voltages are a bit low -- need to watch these, Steering Angle is OK, Fluid Temperature is OK, Door Switch is OFF - OK, Brake Light Switch is OFF - OK, Main Relay Expectation is ON - OK, Ts and Tc are OFF - will think about these overnight, other switches and settings look OK.

When you can ....

• please confirm which are the two DTC's showing on Techstream,
• please advise whether the vehicle is resting on any of the bump stops when at your level place, and also,
• please measure and advise the hub-to-fender heights at all four wheels at the same place,

..... all corresponding to the Techstream screenshot showing the Front and Rear Height Control Sensor readings at the same location.

Measurements are a bit unreliable at anything other than N height because there can be some variations in the way the vehicle moves and some effects if the Front end alignment is out and/or if there is damage at the Rear end -- but at the moment, with AHC not working, there is no choice but to measure the vehicle in its current condition at the most level location you can find.

The idea here is to understand of how much of the Sensor difference might be due to a physical 'lean'? Is the vehicle actually low by a lot by tape-measure at the Front Right??? This also would usually mean that the diagonally opposite Rear Left is high (but depends a bit on any history of wear and tear and/or damage to chassis or body or mechanical suspension components, tyre type, pressures and wear being similar) -- but please tape-measure at all four wheels anyway.

If the Sensor readings are not accounted for by a physical 'lean' of the vehicle, then one or all of the Sensors (or circuits) are suspect -- mal-adjusted or faulty -- assuming that the Front end geometry and Rear end geometry is in reasonable shape, meaning no components, nor chassis, nor body are measurably damaged.

At N height, unless the vehicle has been 'lifted', for example using Sensor adjustments, and if is basically in 'stock' condition, then around 19.75 inches (500 millimetres) hub-to-fender both sides at the Front would be good (if 19.50 inches also is OK) and 20.50 inches (520 millimetres) hub-to-fender both sides at the Rear also would be good.

If stuck at LO (not on bump stops) then would expect around 50 millimetres less at the Front, around 40 millimetres less at the Rear -- regard these numbers as guides, not measuring to the millimetre here:

View attachment 3292189

If there is a 'lean', it is worth trying to correct this with the torsion bar adjusters, (engine OFF, do not want AHC system to suddenly 'wake up'), needs a good squirt of some kind of thread penetrating fluid on the adjuster threads the day before, then needs a 30 millimetre socket, a strong arm and possibly an extension bar or pipe of some kind, then see yet another attachment below labelled "AHC cross level per FSM".

In this step you are just trying to equalise Front Left and Front Right physical hub-to-fender tape measurements -- and if a tape-measure is available just use string or a marked stick -- don't worry about actual 'ride height' measurement numbers too much until AHC is working again -- because it is the AHC system and the Height Control Sensor adjusters which will be used to set 'ride height' eventually, not the torsion bar adjusters on an AHC-equipped vehicle.

So after Front 'cross-levelling', measure and record hub-to-fender at all four wheels again. Read and record Front Height Control Sensor reading and Rear Height Control Sensor again. (Note that height control is only Front and Rear on LC100/LX470 -- height at each wheel is not individually controlled by the AHC system on LC100/LX470).

Re-start engine. Re-start AHC system by pushing down ON/OFF switch for ~10 seconds, all doors and rear hatch closed, vehicle in PARK, foot OFF brake.

If you get a lucky break, this might be enough -- but I really think that there will be more to do.

Anyway, enough for today. Please consider -- and when you can, please provide an update with data as requested above -- and a path forward then can be discussed ......

By the way, if you can recall, please also advise what the AHC pressures may have been when the AHC system was last operational. Also suggest look for signs of AHC Fluid weeping at the 'shock absorbers' -- this may indicate a history of excessive AHC pressures.

It's pouring rain here so we are all stuck in the tent.

Can't get out to Measure Hub to fender right now but I will say I don't notice the lean anymore. I'll measure as soon as I can.

In response to your other questions

Codes

c1762 Abnormal oil pressure for pump

C1751 Continious current to compressor motor.

It's also NOT resting on the bump stops. It looks like low setting.

Previously the AHC worked perfectly. It's only after I played with the height sensors that everything went to hell. Shocks not leaking. All was good.

I can't tell you about previous pressures as I only got Techstream going after I was hit with the problem.

Cross Levelling won't happen our camping as I don't have the tools but I'll try to get out to measure later this afternoon.

My sense is that this is 100% Sensor related and the lean I observed my have been some anomaly. It was certainly not there prior to the problem and it has new springs in the back.

I feel the best way forward for now might be to adjust the Sensors back to spec. Can you tell me what numbers I should be aiming for?

 

[Skruf]

Ok

500mm on all corners except right rear which is 480.

I notice you've said in a previous post that this is the nominal ride height.

Ive got photos of the car in low, medium and high from a few months back and what I'm seeing now is the height that was previously the low setting.


Dunno what the story is there. It was not modified in any way prior to me getting my hands on it. (Added pics for illustration of low medium high)

I also went ahead and adjusted the 3 Sensors so they're within 5mm of each other (45 -50)

Cleared faults

Still throwing a code and defaulting to low. Seems to only be throwing c1762 now

 

[Skruf]

Ok I made it back home.

Something interesting.

I had the vehicle well loaded up and it was riding close to the bump stops.

When I got home and unloaded the rear suspension rose to 520mm (LR) and 530mm (RR) so that would seem to indicate that the AHC was (at least in some limited capacity) pressurizing the system to compensate for load?

The front suspension was reading 475 (LF) and 490 (RF)

Something I forgot to mention. At the same time I tried to do a sensor lift at the front I also cranked up the torsion bars - 5 turns each side.

I figured its a 24yo vehicle and its probably never been adjusted so without techstream I just put some more tension into it (stupid I know).

What I've done now is removed 5 turns from the right side and now the vehicle is sitting evenly

RR 520mm
LR 520 mm

RF 475mm
LF 475mm

The rear sensor is reading zero
the front left and right are reading -46 (I adjusted them to be equal)

Now I think if my previous experience repeats as soon as I start driving it the rear will drop down to be about equal to the front.

I cleared codes and started it up. You can hear the pump working and it sounds like its blocked or dry. Its straining and loud.

Still the same codes.

What to try next?

 

[IndroCruise]

Ok I made it back home.

Something interesting.

I had the vehicle well loaded up and it was riding close to the bump stops.

When I got home and unloaded the rear suspension rose to 520mm (LR) and 530mm (RR) so that would seem to indicate that the AHC was (at least in some limited capacity) pressurizing the system to compensate for load?

The front suspension was reading 475 (LF) and 490 (RF)

Something I forgot to mention. At the same time I tried to do a sensor lift at the front I also cranked up the torsion bars - 5 turns each side.

I figured its a 24yo vehicle and its probably never been adjusted so without techstream I just put some more tension into it (stupid I know).

What I've done now is removed 5 turns from the right side and now the vehicle is sitting evenly

RR 520mm
LR 520 mm

RF 475mm
LF 475mm

The rear sensor is reading zero
the front left and right are reading -46 (I adjusted them to be equal)

Now I think if my previous experience repeats as soon as I start driving it the rear will drop down to be about equal to the front.

I cleared codes and started it up. You can hear the pump working and it sounds like its blocked or dry. Its straining and loud.

Still the same codes.

What to try next?

In the absence of other ideas from other IH8MUD members may I suggest as follows ....

Best to show your own Techstream screenshot after the above changes.

A Techstream screenshot of typical healthy system would like the image below with vehicle behaving normally after N > LO > N movements and with Height Control Sensors adjusted close as possible to zero at N, Front cross-levelled with equal tape-measured physical heights at N, and with AHC pressures at N within FSM-specified ranges by adjusting Front torsion bars and making changes to Rear springs, with spacers or upgraded springs or airbag inserts for temporary loads.

In your case, as well as the reported Height Control Sensor readings and tape-measured hub-to-fender heights, what is now happening to the following?

• AHC pressures – Front, Rear and Height Control Accumulator,
• Main Relay Expectation (should show “ON” -- if “OFF” then no power to AHC system and no AHC movement, could be a faulty AHC Main Relay but more likely a ‘fail safe function’ initiated by the ECU due to some other fault),
• Front Wheel Step (should show 8 when testing a stationary vehicle -- if zero as seen previously, possible problems at Front Damping Force Control Actuators but more likely to be Height Control Sensor problems, also good to look at this while the vehicle is in motion with Techstream connected, another person driving),
• Rear Wheel Step (should show 8 when testing a stationary vehicle -- if zero as seen previously, possible problems at Rear Damping Force Control Actuators but more likely to be Height Control Sensor problems, also good to look at this while the vehicle is in motion with Techstream connected, another person driving).

C1751 and C1762 – if continuing, may be a consequence of ECU adopting ‘fail safe function’ due to one or more of

• air (or nitrogen) in the AHC Fluid, AHC Pump spending time and effort compressing gas rather than raising the vehicle, or,
• very wide differences in Height Control Sensor readings (both Front Sensors equal at negative 46 millimetres (or inches?), Rear Sensor zero (or close to zero), inevitable ‘fail safe function’ due to large differences in Sensor signals which ECU cannot resolve, or,
• partial AHC Pump Inlet Strainer blockage reducing flow of AHC Fluid into the actual gear pump – would also mean a noisy pump as in your description and inevitable C1751 and/or C1762, or,
• a worn AHC Pump also would mean a noisy pump as in your description with similar DTC’s,
• possible failure of AHC Main Relay (located under the dashboard on/near Suspension ECU -- this is possible but low probability, check other causes first.

Note that your vehicle is of an age for which the attached Toyota/Lexus Technical Service Bulletin 3006 applies – in which debris from a failed O-ring within the Height Control Accumulator causes a blockage at the Inlet Strainer within the AHC Pump (nothing to do with the strainer at the top of the AHC Tank).

A downstream blockage causing the AHC Pump to labour too hard would be expected to show DTC1763 and/or DTC 1764. Have either of these DTC’s been seen?

The observation that the vehicle goes to lower heights on the road means either that

• the vehicle and the AHC system is overloaded, or,
• the AHC system is not working correctly due to ‘fail safe function’ initiated by the ECU, or,
• there are faulty Levelling Valves in the Control Valve Assembly -- the Levelling Valves are ‘normally closed’ allowing no AHC Fluid movement unless the Levelling Valve are opened by a signal from the ECU.

Where to start?

If this were my vehicle, I would do the following, in this order:

• Test the AHC Pressure Sensor located at the AHC Pump per method for your model year per FSM to ensure that this is not the 'root cause' of all other problems -- unlikely but possible, replacement is expensive, if necessary use VIN on Partsouq to find correct Part Number -- there are differences between model years,

• If the vehicle can be raised, bleed the system -- before starting have on hand at least two x 2.5 litre cans of genuine Toyota/Lexus AHC Fluid Part Number 08886-01805 -- according to your posts this system was opened when the Attenuator was flushed, so it cannot be assumed that there is no air in the system. Before that, your posts reported bubbles when bleeding the Height Control Accumulator. These came from somewhere, either air in the system or nitrogen leaking through membranes in aged and failing ‘globes’. Suggest read this long thread to be persuaded -- start at the end of this very long story by @aharlan001 -- see Post #243 at AHC Inop after fluid change 2007 lx C1751 and C1762 - https://forum.ih8mud.com/threads/ahc-inop-after-fluid-change-2007-lx-c1751-and-c1762.1233088/page-13#post-13517321, then go back to the beginning and skim forward to see what was involved, Note that this problem also started with C1751 and C1762 and was resolved by a huge amount of persistent and repetitive bleeding to get air out of the system,

• If it is possible to raise the vehicle to N to start bleeding the system, especially note whether there are persistent streams of fine bubbles at any of the bleeders next to the four ‘globes’. This would suggest nitrogen leaking through failing ‘globe’ membranes, especially if ‘globes’ are original and 24 years old. The ‘rule of thumb’ is 10 years for life for ‘globes’, although some do better and some do worse,

• If vehicle can be raised, do a preliminary check of overall condition of the four ‘globes’ by observing the differences in AHC level at the AHC Tank at LO height compared to HI height -- preliminary, because this test should be done after the vehicle is at FSM-specified AHC pressures at N height -- then a difference of ~14 graduations between LO and HI means ‘globes’ are similar to new, and at 7 graduations or less, damping will be poor and all four ‘globes’ should be replaced (especially if there are suspicions about nitrogen leaking through membranes in old ‘globes’). Replacement Part Numbers are: Front 49141-60010 -- two required; Rear 49151-60010 -- two required. Suggest check Partsouq and Impex prices,

• If the vehicle can be raised to normal N height, either by self-levelling itself with AHC system operating or by using the he "Height Control Operation Test (Active Test)" as posted previously (using a paper-clip) or using jacks or other methods, then set all Height Control Sensors as near as possible to zero,

• Again, if vehicle can be moved N > LO > N to measure AHC pressures, adjust Front torsion bars to bring Front AHC pressures into FSM-specified range and consider what to do about Rear AHC pressures if necessary – spacers, or new OEM springs, or upgraded springs, or airbags (maybe King KTRS-79 springs already are in place (?), in which case expect low AHC pressures and a slightly more firm ride when there is no load in or on the vehicle),

• If the vehicle cannot be raised (and in any case given the 24 years of age and 400,000 kilometres of the vehicle), and does not respond to a carefully and accurately executed “Height Control Operation Test (Active Test)” with paper-clip as previously described, suggest start with suspicions about the Height Control Sensors: remove all of them, test all of them per FSM method or using the @PADDO method --- see 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 . Replaced failed Sensors with genuine Toyota/Lexus or AISIN parts. Sensor problems are expected at this age/mileage – Sensors are wear items like brake pads or tyres etc.

• On a 1999/400,000 kilometres vehicle, if Height Control Sensors are original, they are now ~24 years old. They are 'wear items'. If the carbon track is not showing signs of wear, then these wear conditions will arrive sooner than later -- reduced thickness, changed resistance, changed voltage outputs around heavy wear point at mid-swing of Sensor arm at N height), and/or reduced brush pressure (weak contact, variable effects on voltage output), and/or the beginnings of corrosion or 'tracking paths' inside the Sensor, .
  
  Suggest cut to the chase, check Partsouq and Impex pricing, and replace:
  
  Toyota/Lexus Height Control Sensors – Part Numbers:
  89405-60012 (Front Right)
  89406-60022 (Front Left)
  89407-60010 (Rear)
  
  Or consider AISIN Sensors -- because AISIN are suppliers to Toyota/Lexus:
  
  Aisin Height Control Sensors – Part Numbers:
  HST-020 (Front Right)
  HST-021 (Front Left)
  HST-026 (Rear)

• Suggest avoid short-life disappointment with unreliable cheap fake replacement Sensors, and avoid secondhand Sensors unless tested and opened and physically inspected,

• If Sensors test OK or are replaced and symptoms continue, test Sensor circuits for continuity – suggest use the Electrical Wiring Diagram (EWD) for your vehicle and start with BI1 and BI2 connectors found high up inside LHS Rear quarter panel. This can be a long PITA job!

• Consider AHC Pump noise -- remove AHC Fluid, remove whole AHC Pump/Motor/Tank assembly, remove and replace AHC Pump sub-assembly Part Number 48901-60010. Some ideas and pictures can be found here (LHD vehicle): AHC pump removal with pics - https://forum.ih8mud.com/threads/ahc-pump-removal-with-pics.1227554/#post-13401739,

• Lots more information and pictures about the AHC Pump sub-assembly Part Number 48901-60010 and the internal strainers at links within this post: AHC Time LO to N, N to HI, LO to HI - https://forum.ih8mud.com/threads/ahc-time-lo-to-n-n-to-hi-lo-to-hi.1303123/page-2#post-14849640 ,

• AHC Pump sub-assembly Part Number 48901-60010 can be disassembled opened and cleaned as described and pictured in the above references -- but frankly given the age/mileage of the vehicle, replacement of 48901-60010 is the better idea -- look at Partsouq and Impex prices -- suggest buy and fit (it is not difficult work):

48901-60010 – AHC Pump sub-assembly (and maybe the whole works 48910-60012 -- but this is expensive!)
90311-10001 - oil seal between AHC Pump and Motor
90301-70003 – large O-ring for AHC Pump,
90301-06012 – small O-ring for AHC Pump,
47255-60010 – grommet between AHC Tank and AHC Pump,
49189-60010 – replacement bleeder valves (5 required),
49177-60010 – replacement bleeder caps (5 required)

Consider replacement of Height Control Accumulator Part Number 49130-60010 with second-hand unit younger than the date given in TSB 3006.

If you need some Factory Service Manual (FSM) references for AHC/TEMS, these are found here:

Techstream Error - https://forum.ih8mud.com/threads/techstream-error.1308912/#post-14901269

 

[Skruf]

Hey thanks again for all the great info.

There's obviously lots of possibilities as to what is going on but given that the problem only occurred after me messing with front sensors would this nor indicate a simple adjustment problem?

It just seems unlikely that many of these possibilities like pump failures or sensor failures would occur at precisely the time I mess with the sensors unless the sensor changes caused something to overload and fail.


You've mentioned the wide variance between sensors readings inevitably causing it to go into safe mode.

Would not a first step be to adjust all these sensors to be the same and see if it raises? If so while stuck on low, what should they be adjusted to?

Anyway I took it for a drive after the adjustments I made in the previous post.

Threw 1762

Doesn't always default to safe mode. Often just goes to low.

Not wanting to monopolise anymore of the generous time you've put into helping me, I'll try to work through your list and see what happens

Cheers

 

[IndroCruise]

Hey thanks again for all the great info.

There's obviously lots of possibilities as to what is going on but given that the problem only occurred after me messing with front sensors would this nor indicate a simple adjustment problem?

It just seems unlikely that many of these possibilities like pump failures or sensor failures would occur at precisely the time I mess with the sensors unless the sensor changes caused something to overload and fail.


You've mentioned the wide variance between sensors readings inevitably causing it to go into safe mode.

Would not a first step be to adjust all these sensors to be the same and see if it raises? If so while stuck on low, what should they be adjusted to?

Anyway I took it for a drive after the adjustments I made in the previous post.

Threw 1762

Doesn't always default to safe mode. Often just goes to low.

Not wanting to monopolise anymore of the generous time you've put into helping me, I'll try to work through your list and see what happens

Cheers

View attachment 3298697

I certainly hope that you are right -- and that it is just a Sensor adjustment problem -- but if I really thought so I would have said so -- but I have been wrong before!!

Just to be clear, the list offered above is meant as a 'batting list' -- suggesting the order in which causes might be eliminated logically having regard to the way the system works. It is not a random choice of possibilities.

There are other things which could be added at the end of the given list -- for example, are there problems with the Damping Force Control Actuators causing the Front Wheel Step and Rear Wheel Step to show as zero rather the expected Step 8.

There are some even more obscure causes of AHC issues -- but far and away the most common cause of AHC malfunctions are Height Control Sensors or the Height Control Sensor circuits/harnesses/connectors.

The inconsistencies and wide differences of your Height Control Sensor readings -- now FR negative 54.8 millimetres; FL negative 34 millimetres; Rear negative 15.2 millimetres -- different compared to your previous readings --along with the reported behaviour of your vehicle are all strong clues that at least one of your Sensors is a dud. The idea that the Sensors were OK previously and should be OK now, just a matter of adjustment, does not really wash. The Sensors are simple brush-on-carbon-track potentiometers signalling in fractions of a Volt to a very fussy ECU. It is not just plausible but highly likely that at least one old, worn Sensor or poor connection or damaged wiring somewhere has been sufficiently disrupted to choose this moment to play difficult -- a bit like shaking an old incandescent light-globe which worked yesterday but today it doesn't.

A way of guessing the Height Control Sensor readings at LO might be to take the details in the table at Post #21 in this thread (this comes from the FSM) and at LO height set the both Front Height Control Sensors at negative 50 millimetres and the Rear Height Control Sensor at negative 40 millimetres -- or eliminate all differences and set them all at negative 50 millimetres . I have never tried this and have no idea whether it will work -- but it cannot hurt to try and cannot do any damage. [Note: If ever using the “Height Control Operation Test (Active Test)”, just be careful of the warning in the procedure which states: “Do not raise the vehicle height higher than the ”HI” position when raising it with the active test”].

The ECU will either like the signals or it won't and it will behave accordingly. There is no way that the Sensor changes will cause something to overload and fail. The multiple 'fail safe functions' protect against that. When the ECU dies, nothing will happen in the AHC system at all except maybe the appearance of the dreaded DTC C1761 indicating that the ECU has a memory fault and is effectively dead.

Anyway, the best way forward now is for you to try a few things 'hands-on' as a way of experimenting and finding out what causes what.

Hope it all works out!!

 

[Skruf]

I certainly hope that you are right -- and that it is just a Sensor adjustment problem -- but if I really thought so I would have said so -- but I have been wrong before!!

Just to be clear, the list offered above is meant as a 'batting list' -- suggesting the order in which causes might be eliminated logically having regard to the way the system works. It is not a random choice of possibilities.

There are other things which could be added at the end of the given list -- for example, are there problems with the Damping Force Control Actuators causing the Front Wheel Step and Rear Wheel Step to show as zero rather the expected Step 8.

There are some even more obscure causes of AHC issues -- but far and away the most common cause of AHC malfunctions are Height Control Sensors or the Height Control Sensor circuits/harnesses/connectors.

The inconsistencies and wide differences of your Height Control Sensor readings -- now FR negative 54.8 millimetres; FL negative 34 millimetres; Rear negative 15.2 millimetres -- different compared to your previous readings --along with the reported behaviour of your vehicle are all strong clues that at least one of your Sensors is a dud. The idea that the Sensors were OK previously and should be OK now, just a matter of adjustment, does not really wash. The Sensors are simple brush-on-carbon-track potentiometers signalling in fractions of a Volt to a very fussy ECU. It is not just plausible but highly likely that at least one old, worn Sensor or poor connection or damaged wiring somewhere has been sufficiently disrupted to choose this moment to play difficult -- a bit like shaking an old incandescent light-globe which worked yesterday but today it doesn't.

A way of guessing the Height Control Sensor readings at LO might be to take the details in the table at Post #21 in this thread (this comes from the FSM) and at LO height set the both Front Height Control Sensors at negative 50 millimetres and the Rear Height Control Sensor at negative 40 millimetres -- or eliminate all differences and set them all at negative 50 millimetres . I have never tried this and have no idea whether it will work -- but it cannot hurt to try and cannot do any damage. [Note: If ever using the “Height Control Operation Test (Active Test)”, just be careful of the warning in the procedure which states: “Do not raise the vehicle height higher than the ”HI” position when raising it with the active test”].

The ECU will either like the signals or it won't and it will behave accordingly. There is no way that the Sensor changes will cause something to overload and fail. The multiple 'fail safe functions' protect against that. When the ECU dies, nothing will happen in the AHC system at all except maybe the appearance of the dreaded DTC C1761 indicating that the ECU has a memory fault and is effectively dead.

Anyway, the best way forward now is for you to try a few things 'hands-on' as a way of experimenting and finding out what causes what.

Hope it all works out!!

Hey just an update, I bought and fitted new sensors all round. Still no joy. Still throwing the same codes.

I bought the AHC pump sub-assembly too but some of the o-rings have been hard to obtain so still waiting on them to get to me. Once they arrive I'll fit.

I notice if I try to raise the vehicle with the bonnet open.... If I feel the outlet of the AHC pump I can feel it cavitating, it feels like its full of air and straining. Oh and now its sitting on the bump stops at the back. That doesn't seem like a positive development

Probably not much point in doing anything until the other bits arrive.

The one thing I haven't done is test the AHC Pressure Sensor. Just trying to track down a service manual. Any suggestions for a good publication?