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My air suspension has no leaks and the compressor has no problem raising the car. In fact, the car always raises with the reservoir and the compressor only runs 15-30 seconds to recharge the reservoir. The front air springs are recently new, no "vehicle too low" messages, no sagging overnight, no other fault messages or codes.
However, I've noticed an issue that seems to be getting more frequent. the front height keeps changing, from too high, to too low (but not enough to set a malfunction warning), like 1 out of every 5 drive cycles. The rear height is always perfect.
The odd thing is that when I park the car, the height always goes back to the correct level. I.E. if I stop and notice the car is 3" high up front, once I shut the engine off the system immediately releases air and the front goes back to normal. Likewise if it's too low, when I restart the front lifts up to the correct height. Doesn't seem to correlate to driving over abnormal roads or anything, I pretty much drive the same roads every day.
I did not try resetting the height calibration in SDD yet. My intuition is saying that the front height sensor has gone (or is going) bad. I've read on this forum about people encountering a bad height sensor that causes one corner to go up to full height, but mine seems rather intermittent.
Should I get a new sensor and just replace it? Or should I try a calibration first? My other thought was to pull the front sensor connector and clean that, but the fact that it levels perfectly with the car parked would point to something else.
I had a similar issue with the front raising and lowering intermittantly on my 2004 XJR. The front left ride height sensor was replaced twice but did not resolve the issue. Eventually the cause was found to be a broken wire in the harness about six inches back from the sensor connector at the rear of the wheel arch. The cable had rubbed on the split plastic tube they protect it with and eventually worn through. I proactively checked the same on my 2004 XJ6 when replacing the brakes and found it too had partially worn through the insulation in a couple of places. I spliced in a new length of wire and replaced the split ribbed plastic tube with a length of airline from my aquarium to prevent it happening again.
If you have access to SDD then I believe there is a resistance test you can do to live-read the sensor. You could then have someone wiggle the harness by hand to see if the resistance changes. Failing that you can easily access the air suspension module behind the rear seat back and using the schematics you can identify which wires go to the sensor and test them directly.
I had a similar issue with the front raising and lowering intermittantly on my 2004 XJR. The front left ride height sensor was replaced twice but did not resolve the issue. Eventually the cause was found to be a broken wire in the harness about six inches back from the sensor connector at the rear of the wheel arch. The cable had rubbed on the split plastic tube they protect it with and eventually worn through. I proactively checked the same on my 2004 XJ6 when replacing the brakes and found it too had partially worn through the insulation in a couple of places. I spliced in a new length of wire and replaced the split ribbed plastic tube with a length of airline from my aquarium to prevent it happening again.
If you have access to SDD then I believe there is a resistance test you can do to live-read the sensor. You could then have someone wiggle the harness by hand to see if the resistance changes. Failing that you can easily access the air suspension module behind the rear seat back and using the schematics you can identify which wires go to the sensor and test them directly.
Thank you so much!! That will be the place to start. Makes much more sense than throwing money at a sensor that may not be bad!
I'd definitely start there as it having affected both of mine suggests a possible design fault with the earier cars. The fact your car returns to normal height when left does hint towards it being a sensor or harness issue rather than on the pneumatic side.
It is easy enough to each to check too - unlike removing the sensors which are an exercise in knuckle scraping. If you have access to a ramp you don't even need to remove the wheels, and if needed both ends of the harness are accessible without removing half of the car.
Depending on you model you may have either the 4 sensor or 3 sensor version
If you have the 4 sensor and it has an update to the ASM it will be using 3 sensors
Any of the sensors not just the front can cause an issue on one corner via weight transfer
The easiest way to eliminate the harness and sensors is to bypass them.
The ASM is behind the rear seat.
With car sitting correctly (idle the engine), Measure the voltages on the harness pins for each of the sensors (CR90-2, 5, 8 & 11)
Turn off the engine and attach a variable resistor (1m ohm or greater) to the pins for each sensor.
Disconnect the sensors
Turn on the ign and rotate the variable resistors till the volts are the same on each as you measured
You have now bypassed the sensors and the ASM will think the heights never change
IF they do your problem lies elsewhere
Well, the harness does not seem to be the issue. Looks like Jag resolved any chaffing issue behind the wheel liner. There's a gap now that allows the wires to pass without any problem.
Going to run the calibration today and see how that does. Not expecting much, but worth trying the easier things first.
That's a shame, it would have been an easy fix. Just to double check - from memory on mine the chaffing was where the cable exits the split tubing and it was taped closed, but it had rubbed on the tubing and split under the tape, not the where it crosses the wheel liner.
Having rules out a visual fault I would start with 34by151's suggestion of measuring the voltages and resistance across the pins at the ASM end and matching with a variable resistor as close as you can. If it still moves on its own it follows that it should be either pneumatic or a faulty ASM.
That's a shame, it would have been an easy fix. Just to double check - from memory on mine the chaffing was where the cable exits the split tubing and it was taped closed, but it had rubbed on the tubing and split under the tape, not the where it crosses the wheel liner.
Having rules out a visual fault I would start with 34by151's suggestion of measuring the voltages and resistance across the pins at the ASM end and matching with a variable resistor as close as you can. If it still moves on its own it follows that it should be either pneumatic or a faulty ASM.
Thanks--I will take another look. I misunderstood your original post (at the wheel arch), I didn't even look under the tape where the wire comes out of the plastic tube at the sensor.
Yes, if this doesn't change I will look further into the ASM readings.
Didn't find anything wrong with the wiring to the front sensor. I had looked into getting a replacement/used front height sensor. I felt as though the car was occasionally going into "rough road" detection mode and raising the front height.
But before that, I ran the suspension calibration in SDD and it seemed to have calmed down everything. The front left-right heights were off initially, and the recal fixed that. Since then I haven't really noticed the front being abnormally high.
04-19-2016, 07:03 AM
flakey ride height sensor?
