My wife's 2004 XJ8 (78,000 miles) is constantly showing an air suspension fault but their are no symptoms and no codes being thrown that are being pulled by either OBD ll or the JRL SDD program I'm using. Very frustrating as I can't make it stop and have no clue as to which area to look at. I don't just want to throw money at it since the car doesn't act up at all.

She is also getting on occasion a DSC unavailable as well as an ABS light but they too don't post any codes and she's a lousy diagnostician since she never is able to tell me when it happens or what she was doing when they flashed. I'm thinking they occur when she is a tad too forceful on the gas or brakes as we unfortunately have to drive about 1 mile of dirt road both coming and going every day before we get to the highway from our house.

Anyone have a clue or suggestion as to where to start? It's a lot of work to remove each wheel to inspect and test each ride height sensor, wheel peed sensor, or accelerometer, especially when your not sure just what and how to test them.

 

Lights always set codes. Try the battery disconnect reboot, as it sounds like the ECM is acting up.

 

Easy enough to do so I'll give that a try. She drove my XK8 today so I'll report back when I can.

 

Hi RDMinor,

If there are no symptoms in the air suspension, such as the front end sagging low and not rising when the car is started, then one thing I would suspect is corrosion on ground studs or electrical connectors.

If you haven't cleaned the three grounds behind the headlamps, that would be a good place to start. There's one behind the left headlamp and two behind the right headlamp (the lower of which is difficult to access). Clean the threaded studs, ring terminals on the wires and flat surfaces of the aluminum nuts with a brass brush (not sandpaper) and zero-residue electrical contact cleaner spray. Take care when retightening the aluminum nuts because the torque specification is just 6.5 lb-ft / 9 Nm. Several members have accidentally snapped off the aluminum threaded posts. Off the top of my head, the ground behind the left headlamp is used by the air compressor, and the ones behind the right headlamp are associated with circuits in the front power distribution fuse box, where the main air suspension relay resides.

On these aluminum grounds, the corrosion is a thin whitish coating that increases electrical resistance just like rust does on steel terminals.

Cheers,

Don

 

Good advice, and when everything is back together and tightened up, spray some corrosion inhibitor all around the ground points. It stops further corrosion starting. I did this when I bought my car in 2010, and do it every year, and so far, (in 2014) I have had no problems.

 

Good suggestion as I'm having no issues with the mechanical side of the air suspension. I do, however, have an on going issue with an air suspension fault message that comes on with the key every time. No overnight deflation issues, etc., yet the fault message shows up every ignition cycle. That's another issue with no code but I'm working on that separately from the ABS/DSC issue.

I'll take a close look at the forward grounds as you suggest as they would be more likely to be affected by the environment than the ones in the trunk which are in excellent shape.


I'll report back when I've had a chance to check them out.

I've also heard that a bad or dirty wheel speed sensor can also cause such lights but wouldn't they leave a code?

 

Funnily enough there was a guy on this forum in Australia who had a yellow light come up

every time he drove down the unsealed road from his house.

He had Jaguar look at it including a "Jag Master Technician"! look at it but they couldn't

fix it.

I told him it was probably the seal on the compressor and told him where to get a

replacement from. Problem fixed.

Your other fault will probably be dirty ABS sensor/failing sensor/dogey wiring or connector.

You could wait until the fault gets worse and maybe SDD will the see it.

 

When the compressor seal was gone in my XJR the air suspension fault warning would come on a random times, I distinctly recall it came on once after hitting a pothole, so i agree that somehow the rough road could be triggering it. Never saw the warning again after fixing the compressor.

Also worth mentioning that you should check the battery. If you have a volt meter that can record min/max then hook it up and record the voltage drop when starting the engine. These cars are known to throw up random messages when starting if the battery voltage drops too low while cranking.

 

I'm leaning towards a compressor fault although I did use one of Andy's repro seals to rebuild it when I also replaced the right front air shock. The error message now comes on as soon as the engine cranks up. The compressor kicks in initially nut does cut off well before the 2 minute timer kicks in.


I'll check the battery although it looks to be relatively new but I have a good Fluke multi-meter so testing it takes no time at all. I'm installing a CD changer so the trunk is pretty well taken apart all ready<G>