I bought my 2006 XJ8 about 2 months ago and the Air Suspension Fault message was displaying. The owner had told me he had had the suspension repaired, but the computer had not been reset. The suspension worked fine for the first month.

About a week ago I came out to find the car sitting very low ... all four "corners" very low so that the tops of the tires could not be seen. Starting the car and letting it sit for a few minutes refilled the suspension and the car drove well. I kept an eye on the car, both when I drove and when it sat. For the next few days there was no change (both on hot days and cool days). During all of this, the Air Suspension Fault error continued to show.

Then, this morning, the car was "flat" again. And, once again, starting the car quickly inflated the suspension. It's been half a day and the car looks fine (no loss of air in the suspension).

What do you think is going on? If it were a leak, wouldn't I be consistently losing air and finding the car "flat" each morning after sitting all night?

Thanks for any help.

 

Basically, yes, a leak is always there, but this forum is no stranger to Jaguar air suspension peculiarities !
The main thing is to get the stored fault codes read. The air suspension eventually goes to 'Sleep' mode and does nothing for 24 hours, then wakes up, checks the vehicle height and then if it's out of range, tries to level the vehicle. If raising is needed, it uses the pressure in the reservoir tank in the trunk.
Really, at the stage you are at, there is no alternative to reading off the fault codes to see what might be happening.

 

The Messaging system doesn't work that way. If he had had the system repaired, the fault wouldn't be displayed on the message center. Yes, there would be stored DTCs from before the repair, and those would have to cleared from memory, but that's different.

If the fault is coming up on the message center that means that the system is failing a real time test.

The two most likely culprits are a pump with a worn piston ring or a shock with a slow weak. Either can cause the system tests to fail because it takes too long to reach proper setup.

Don't know if you have any recourse with the prior owner, but if you do you should follow up on that.

 

If it were a leaking 'shock' then I think only that corner would be affected; I don't see how it could affect the other three. Like Fraser says, you really need to get the fault codes (DTCs) read to find out what's going on.

 

It affects the other 3 shocks when the system wakes up every 24 hours and levels the car to the lowest point (hence the one shock that is leaking)

 

True, but I'd rather assumed the OP used the car daily which would be too frequent for the 24 hr wake up to occur.

 

Okay! There were a lot of codes on the car. Apparently many had not been cleared from previous things. But here are the one(s) for the air suspension:

C1830 - Air Suspension compressor relay - circuit failure
C2303 - Reservoir plausibility error

 

What those two codes are basically saying is that the compressor/system can't keep up with air demand to return the system to specs within a specified period of time.

I would recommend as a first step, you swap the compressor relay out with the same type from another location (I can't recall off the top of my head which ones are the same the type). You should also use contact cleaner (not WD40) to make sure the relay has a clean current flow.

If that doesn't solve it, your next step would be to install BagpipingAndy's compressor rebuild kit. One, it will eliminate one of the most likely causes, and given the car's age, it's time to do it anyway (it's a DIY project if you are game).

If after doing the compressor rebuild, you are still getting faults, it means you have a leak or some kind of wiring fault. We can help you pinpoint or identify the leak.

Here is a link to the rebuild kit:

Jaguar XJ6 XJ8 XJR X350 Wabco Air Suspension Compressor Pump Seal Repair Kit | eBay

I would do the rebuild kit regardless if the relay solves it or you have a leak.

 

To add to Mac Allan - swap R4 and R1 relays to see if your relay issue goes away. Yes, compressors working too hard will either fry or lock the relay.

You can also bench test the compressor relay w/ 12V.

 

Thanks. Now, where can I find out where these relays are (R4 and R1)?

 

Engine compartment power distribution/fuse box

 

Alright, two (more) things!

1) I swapped out R1 and R4. Not to sound too dumb, but what do I do now? Wait and see if the car ever goes flat again? The Air Suspension Fault error is still showing (but I am guessing that will keep showing until cleared?).

2) After popping the lid off the engine compartment fuse box, I noticed that there is NO relay for R3! It is empty! Should there be a relay there?

 

I do have R3

 

I'm having trouble finding what the relays actually are (the owners manual lists the fuses, but not the relays). Some digging shows that R3 is a "RH Windshield Heater"? Is this correct?

 

If you mean that "Air Suspension Fault" shows on the message center in the middle of the Instrument Cluster, it means that swapping your relays didn't solve the problem.

The DTCs do not have to be cleared for the fault message to go away. That message is telling you that the system is failing a real time test sequence. Once the fault is gone, the message will go away.

I suspect that you have a weak pump that should be rebuilt ASAP, and a leak.

 

As stated earlier, I swapped R1 and R4. That did not clear the code, so, as Mac Allan pointed out, the issue is still there. However, swapping them caused my intermittent wipers to not work properly. When I looked at the codes printed on the top of the relays, I saw that they were ever so slightly different. The codes were the same for relays 1, 2 and 5. Putting the relay from R4 back in R4 fixed the intermittent wiper issue. So, are we actually supposed to swap R1 with either R5 or R2 instead?

PS - For giggles I did that. The code still did not clear.