2004 XJ8 Air Suspesion Failure Parameters

I’ve recently been receiving the P2302 error code erratically on my 2004 XJ-8, frequently having it disappear for days, only to reappear again. It can appear when driving, or suddenly show up after the car’s been driven, shut off and restarted. I’ve searched the forum for similar issues and elsewhere found a YouTube posting by Bagpipingandy. Reading various commentaries, I understand this may be an indication of a failing compressor seal, but may also be due to other components in the system.

Before I pull out the compressor and order a replacement seal, I wonder if someone can give me some idea of what the normal functioning parameters of the system are. If the car sits overnight, height from ground to the bottom edge of highest point on front fender wheel arch is 28 inches for both sides, prior to engine start. Upon start, both sides will visibly and quickly rise one half inch to 28 1/2 inches. At the same point at the rear wheels, the overnight measurement is 27 3/4 inches. Upon start-up, the rear rises approximately 1/4 inch to 28 inches. I cannot hear any specific sounds coming from the area of the compressor nor hissing when I listen around various exterior points of the car. Also, can anyone provide the normal operating pressure at the bellows under the spare tire when the system is charged?

As long as the engine is running, those heights are maintained. The car will sink gradually, after shut-off, but very slowly over a period of time. It remains level from right to left showing identical measurements at the wheel arches

Does this sound like a compressor issue, an air shock issue, or is it some other aspect of the system that needs investigation?

I’ve owned the car for five years. Just prior to my purchase, the owner had the front suspension air shocks replaced. The rears are original. The car has about 100K miles.

Many thanks for any suggestions or observations anyone may wish to offer to help me pinpoint the problem…

Tom G

Hi Tom. It is a nightmare, I has similar issues to you with random ‘Air Suspension Failure’ illuminate up but will reset once turn off the engine and restart.
A shop said it was my front shocks so I replaced both fronts, after a while it showed up again and now the mechanic say it is the rear shocks so once again I had them replaced but to no avail, then came the height sensors but still the same.
Instead of just keep giving money to the mechanic but still have problems, I decided to do the work myself since the hardest part has been done (air shocks).
I changed the air compressor and although it solved the problem it came back after 3 months which then I replaced the air suspension valve block under the spare tyre. Each time the error C2302 popping up. It is all smooth and lush now.
Each time with work I reset and do the calibrations using SDD.
As much as I love my X350 for the space and comfort, I still prefer my old Daimler 6 X300 for the looks and easier maintenance.
Although my reply may not assist in your question but it could be allsorts and new parts finding the weakest links after being installed.

Peter T, thank you for the response to my question regarding the air suspension. After doing additional research, and looking at other possible causes, I decided to replace the sealing ring on the suspension compressor, using the kit provided by bagpipingandy and following excellent instructions provided by the YouTube channel “To The Garage”. Following the instructions a bit too closely, perhaps, since I snapped the exact same bolt as the YouTuber did on his compressor’s cylinder head. Fortunately, the stud broke off with enough shaft showing above the threads to get vice grips on once the head was off and, with a judicious application of acetylene to the compressor body, the broken section could be rocked out and equanimity restored. The kit includes the correct tap for chasing the threads on the three bolt holes, as well as three new bolts with locking film already applied to the threads, the correct gasket as well as the metal ring.

Although re-installation could have used another pair of hands, I found a hydraulic jack useful for supporting the unit while all the fiddly support hardware—springs, cups, nuts and washers— were installed on the three permanently mounted studs. The inner wheel well and front bumper underpanel both needed to be removed. The actual repair and cleaning of the compressor probably took 30 minutes, not counting the panel removals, dropping one horn, removal of various electrical and air hoses and the necessary girding of loins in preparation for the first application of the ratchet. There are plenty of useful examples of this procedure on-line, so I didn’t think a more detailed explanation with photos essential.

My 2004 XJ-8 had 111,000 miles on it around the time the error code first appeared. Prior to my purchase of the car, the PO had both front suspension assemblies replaced by a local Jaguar dealer. Now about two weeks since the repair, the error code has not reappeared. I’ll give it a couple of months before I declare unequivocal success.

Regards,
Tom G