The last few times I loaded the trunk full of stuff I got an ASF on my 2004 XJ8. When I get back in the car after emptying the trunk, even a couple of hours later, the fault is gone. It only flags with the trunk weighed down.

I haven't heard any air leaks, no sags, no changes in handling, no physical symptoms of a problem whatsoever. I can drive the car for dozens of miles with the trunk full after the fault has turned on and I get no drop in ride height even though I'm pretty sure the compressor won't run after the fault has turned on (right?).

I'm wondering if the compressor is having a hard time lifting the rear end to the proper height by providing the extra air and/or pressure to compensate for the extra weight in the trunk. A level sensor issue also crossed my mind.

Any ideas, and especially the exact fix, would be appreciated!

 

First thing to do is get the fault codes read. If all appears normal then the air pump may be on the way out. The usual fault for this is C2303 which has the rather cryptic description of "Reservoir plausibility error". What it's telling you is the pump is not able to maintain pressure in the reservoir within a defined pumping period, (a few minutes). So you either have a leak somewhere or the pump is knackered. Has the pump ever been replaced or repaired ?

 

Pump has not been repaired from what I can tell. The car has 60,000 miles on it. Thanks for the code info.