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!
View attachment 3282361
View attachment 3282353
View attachment 3282352
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’.
