Sequence of events 2005 XJ8L: Wife arrived home and informed me the Suspension Too Low and Suspension Fault Light was on. Went out and started car with no Faults showing. She came home from work the next day and the right rear wheel was fully up (Hyper Extended). I left the car overnight and came out the next morning and both rear wheels in Hyper Extended position. Front wheels normal. Ordered a new OEM Wabco Compressor immediately. I purchased the car in 2008 with 38,000 miles. Now the odometer reads 114,000 miles. Love the car and with the help of this forum and pretty good mechanical aptitude, the car has never been to a Dealership. In fact it has been more than 35 years since having somebody work on one of my cars, and I only purchase used cars. My logic is: Everyone drives a used car. Once off the Dealership's lot, it is now a used car. Why pay the new car price? Anyhow, I started to work. I have spent many hours reading just about every thread on this forum concerning Air Suspension problems. Unfortunately, there has been no post to what I am experiencing. I replaced the Battery since it had never been replaced, and a voltage meter indicated low voltage. I then disconnected air lines from the valve block in the trunk to lower the suspension until the new compressor arrived. I did not think it was a good idea to leave in it Hyper Extended position. I installed the new Wabco Compressor when it arrived. I started the car and the new compressor would not kick on (Run). I proceeded to check all Relays and Fuses. Still did not Run. Proceeded with removing the rear trunk carpeting and checked all connections including the REM, Fuse Block and Grounds. Everything was dry as a bone. I also confirmed that all Height Sensors were in the proper position and plugged in. Jacked the car up individually on all corners with the car running thinking about the height sensors. Ran the car for about 20 minutes and even took it for a short drive thinking I may have to wake up a module. Compressor still not running. One thing left to do is remove the back seat to check the ASM. I found a thread on removing the back seat and, I gave it a quick try, quite honestly, it is not as easy as it looks. (Clips up, down, left, right and how do you gain access to them?) I really do not want to see my Jag on the back of a Flatbed Truck heading to a dealership (Very sad sight) and lose my 35 year record. If I can get some professional advice, it will be accepted and appreciated immensely. Thank you in advance! Please remember, I have spent many hours reviewing posts and have tried or considered all the good advice without any luck.

 

Your compressor.
Make sure the tank pressure is relieved first. Sounds like your rear end being high proves there is plenty of air pressure in the system. That's maybe why the compressor won't kick in.
Failing the above, electrical system.
Can you remove the plugin at the compressor and supply 12 volts to it with a couple leads?
If it runs, then that's confirmed that the pump is ok.
Just thought starters.
Good luck.

Mine took awhile to fire up when I first replaced it. Also wabco from arnott.
Works well now. Noisier than the original but only runs occasionally so I never notice it.

 

If the symptom was too much air in the rear shocks, I would not have thought of replacing the air supply unit. The electronic height sensing and compensation system is the suspect. There is no shade tree rule of thumb for this, it has to be analyzed by a dealer. Just take it there and find out what is happening. Sounds to me like the module is bad if both rears are raised too far since each rear wheel has a height sensor on it.

 

Thank you for your responses. It makes perfect sense relieving air tank pressure and I will do so tonight. I did not go into every detail on my original post. The temperature was quite cold the day my wife got the message. I did remove the old (original compressor), disassembled, shimmed the piston ring, and bench tested. Seemed to work fine. Installed back in car with no luck. Also, I hot wired to the appropriate connector with a spare battery. It would run for 5 - 10 seconds and slow to a stop. Almost like being over pressurized. By this time the new compressor arrived and was installed. I agree, if I do not get a another possible solution from this Forum within a day or so, it is time to get to a dealer and have it professional diagnosed. Again, thanks for the suggestions.

 

Replacing the compressor should not have been your first step. It is most likely a height sensor or the ASM module. Before I junked my air system I put a pressure gauge in the tank.

You can jump the compressor relay to see of it works.

Cam you say coilovers?

 

I am puzzled why you immediately rushed out and bought and fitted a new air compressor without carrying out some basic checks. A compressor failure would not pump up the rear springs, it just provides compressed air to the air reservoir in the trunk, the ASM controls the air springs via the valve block. However, a duff height sensor could cause the symptoms you describe. Are there no fault messages and codes ?

Also be aware that the compressor does not run continually, only when needed, and again this is controlled by the ASM.

 

From experience, the winter always treats my car badly. This season has been no exception. The temperature has been consistently -25 degrees C or colder and the air suspension is constantly lowering when left idle. The nuance of the season:

Front shocks fully inflating and never going down (due to ice in the 'air reservoir' and height sensors not being calibrated properly)

Honestly, as long as the temperature is anywhere near freezing, you can expect some unusual behavior from the suspension.

 

I am going through the same thing, what was your final outcome?

 

Unfortunately this happens all too often. People come on with a problem and never follow up.

Can you say coilovers? There! I knew you could. The air ride system in these cars is junk.

IMHO! YMMV!

My 26,000 lb RV has air ride and operates flawlessly.

 

I agree

 

Well it hasn't happened to me at all and we have had plenty of days below freezing this year, but I can understand problems when you get down to US/Canadian winter temperatures. Water also freezes in railway brakes and has been the cause of quite a few train crashes.

 

I have a Freightliner truck with a 35,000 gvr & the air ride system is original over half a millon miles on it & 12 years old. Why car makers can't get this right is beyond me.

 

My RV is freightliner chassis also. Can adjust the ride height with a wrench.

 

My guess? They don't have nearly as much experience with air suspensions as Freightliner does. And they're too proud or too stupid to learn from experts like Freightliner. And/or they just figure their systems will probably last as long as the warranty so why worry.