Thinking about the
spaber05 symptoms and questions in more detail ….
As PADDO and uHu previously have opined, the messages jumping out of the Techstream reading and experience of
spaber05 and requiring attention are:
- SUDDEN onset of ‘harsh ride’ symptoms, and,
- WILDLY different Height Sensor Control readings from Techstream (or other scanner), and,
- NO PRESSURE READINGS.
The first thing that hits the eye in the Techstream output provided by
spaber05 is the large
difference between the Front Right Height Control Sensor (
+2.2 inches) and the Front Left Height Control Sensor (
-3.2 inches) –
an overall difference of 5.4 inches across the front height sensors. This would suggest a huge lean. This cannot be real. As mentioned by PADDO and uHu (and the FSM) the AHC Electronic Control Unit (ECU) will prohibit the AHC system operation until this large difference is rectified. This is consistent with the symptoms observed by
spaber05
What is going on?
The AHC Electronic Control Unit (ECU) determines what happens in the system – and this is the source of performance information read by Techstream or other scanner. Failures of the ECU itself do occur but are not common.
A
‘slow’ decline of AHC performance most often is associated with ‘globes’ steadily deteriorating over time – but may arise from other things such as old and deteriorating AHC fluid, or deteriorating pump, etc.
A
‘sudden’ deterioration of AHC/TEMS performance (sudden onset of ‘harsh ride’, refusal to raise or lower etc) obviously means something has happened suddenly. The cause may be associated with many things but often this means that one of the many sensors feeding the AHC ECU suddenly is sending conflicting or wrong signals.
If the ECU cannot resolve conflicting input signals, it will self-protect itself and the system and the vehicle, in effect by shutting down and/or not operating correctly until the cause is rectified. Lack of active variable damping then will give a harsh ride which may be particularly noticeable at low speeds in town. The Raise/Lower AHC function may not operate.
The cause may be a fluid blockage somewhere in the system, but a common cause is the deterioration or failure of a sensor which then feeds incorrect information to the ECU.
The front Height Control Sensors sit in the front wheel arches and arguably are in the most exposed environment of any of the many sensors in the AHC system. These two sensors are subject to sticks and stones being thrown up which may damage the adjustable linkages to the sensor or the electrical connector, and/or, spray, deep water, mud, snow, salt which may corrode and weaken the linkage leading to breakage, and/or, enter the electrical connector or the sensor itself, leading to progressive internal corrosion.
The single rear Height Control Sensor may be somewhat less exposed but it also is subject to the same underbody operating environment. In the case of
spaber05 the Techstream reading looks OK (near zero) but take care -- this tells nothing about the internal condition of the sensor.
In addition, there is the expected wear and tear of continuous movement of tiny contactor brushes riding over a carbon track during every millisecond of every vertical wheel movement during vehicle operation over hundreds of thousands of kilometres or miles. The Height Control Sensors literally will ‘wear out’ eventually. Some say that the life of these sensors is about 160,000 kilometres (100,000 miles), others say much longer. The point is that if the vehicle is 15 to 20 years old, then the reliability of the Height Control Sensors is becoming questionable and at least investigation and examination and possible replacement is worthwhile as part of routine maintenance to assure ongoing reliability.
Internal deterioration of the Height Control Sensor is depicted in many IH8MUD posts and easily are found with a Search --
see some examples here . The effect will be to change the electrical resistance inside the sensor, resulting in false signals or no signal being sent by the sensor to the ECU.
Internal corrosion will be invisible and progressive – but eventually a point
suddenly will be reached when no signal or a defective signal is being sent by the sensor to the ECU. The symptoms on the road – harsh ride, raise/lower function does not operate, etc – will then be experienced
suddenly. So ….
- Turn wheel and visually inspect sensor linkages and electrical connectors on the vehicle – look for damage, slippage of adjusters, obvious signs of corrosion. Rectify adjustments or damage – this may involve replacing the sensors.
View attachment 2377372
- Check upper electrical connection which joins the sensor to the wiring harness electrical sensor – find black plug in the engine bay on the lead above the sensor (LHS sensor shown in Right Hand Drive vehicle).
View attachment 2377376
- Check electrical condition of the sensor using the on-vehicle suggestion from uHu .
- Remove sensor from the vehicle (not a difficult job -- front sensors easily accessible, removal involves two attachment bolts, one linkage nut, two cable clips, one electrical connector) and check electrical condition using FSM procedure,
- Remove plastic cover from actual sensor and inspect internally, clean up and re-test,
View attachment 2377400
- Decide whether to replace sensor and/or linkage for reliability.
R - AHC stuck in Neutral. Try to go into Hi/Lo and it will flash the green light at you (with N staying lit solid). Front appears to be stuck in Hi (and feels over dampened/too stiff). Rear looks likeit's sagging lower than it should. No DTC's in Techstream. Did all the active tests and all fuction. Have pulled all the fuses (both interior and under hood) and pulled battery and let sit for 10ish minutes.
