The air suspension of my 05 XJR never ceases to amaze me.... I've been having an intermittent Air Suspension Fault come up. When plugged into the diagnostic system, I get the the message: C2303 Reservoir Plausibility Error. The Air Suspension Fault message doesn't seem to have any particular pattern for the triggering of the fault message. The ASF message usually resets after parking the car for a few hours. Can anyone shed some light as to what a reservoir plausibility error might mean? Thanks

Here you go
Taken from the DTC summary

C2303 Reservoir plausibility error
MIL - M (Message displayed)
Causes - Mechanical / pneumatic fault such as:
– pipe disconnected
– air leak

Cheers
34by151

It's also the telltale code that your compressor is wearing out....

Thanks for your replies. I expect it must be the compressor as I don't seem to have any leaks currently, but the compressor is only three years old though. Car hasn't sagged since I changed the valve block on the pressure reservoir in the boot. Does anyone know where I can get a seal kit for the compressor?

The seal kit is readily available from forum member Andy Fulton (bagpipingandy.com). Andy is a precision machinist who manufactures the rings in his home shop. Here are links to photos showing how I rebuilt our compressor using his piston ring. You don't have to replace the desiccant in the air dryer like I did but it's a good idea if your car has some mileage on it, since the desiccant is only partially-reactivated in normal use.

Cheers,

Don

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Thanks. Since i don't seem to be getting any car lowering, does my conclusion that it's the pump seem reasonable? Are there any air leaks from the suspension that won't result in car lowering?

It's a cheap and easy fix to rebuild the compressor with Andy's kit. I'd look at that first to see if your trouble goes away. DonB's post above has great instructions.

Not sure what you mean by "...don't seem to be getting any car lowering..."

If you mean the suspension seems to inflate properly and is not riding lower at one corner compared to the others, then it is most likely that your compressor is just taking too long to inflate the system (which triggers the fault code), but it eventually gets the job done, so the suspension behaves normally.

If you mean the suspension seems to be too high or overinflated, you might have issues with the valve block next to the air reservoir in the trunk/boot. Might be worth checking and cleaning the electrical connectors there, as well as the ground points in that area.

Another possible problem is the exhaust valve in the compressor may not be opening to relieve excess pressure. When you shut off your engine, listen for a hiss of air from the front left corner of the car. This is the exhaust valve opening to allow dry system air to backflush the desiccant in the air dryer to partially reactivate the desiccant, and to relieve the pressure in the line between the compressor and valve block to make it easier for the compressor to start the next time the engine is started. If you don't hear a hiss if air escaping, your exhaust valve may be corroded internally or the electrical connector may be corroded.

Air leaks are common on these suspensions. Look for the recent thread about Viton O-rings for some information that may help address common leak points in the suspension. I intend to replace all the O-rings in our system this summer.

Cheers,

Don

a weak compressor could be the reason for the intermittent error,

you can get my kits through my web link below:

www.bagpipingandy.com

also i now have a distributer in the USA so i can get kits to you you US guys in 1-3 days , still buy on ebay as normal and i sort the rest out.

best regards

andy

Thanks. I used to find that the car would go flat once in 2-3 days with a "car too low message". This improved after I replaced a pair of leaking front shocks but would still occur maybe 1-2 times a week. So had the valve block replaced and that seemed to solve the problem but I would still get the air suspension fault error message.

The car doesn't seem too high, or too low. It's just that this message comes up while driving and doesn't go off until the car is parked for a while. I can't say I've noticed the air release after shut down recently but it used to be there previously. Have to listen out. Hopefully it's just the pump seals. I've just ordered the seals and will have them done. Hopefully that solves the problem.

Thanks. I just ordered 2 sets from you (one for the current pump and another for the previous pump that I still have in my spares collection). Hope it solves the problem.

Please report back after you've rebuilt the compressor to let us know if it resolves your issues. We're all trying to learn everything we can about the misbehavior of these air suspensions so we can be more effective in diagnosing problems, and every success story helps.

Cheers,

Don

Will do. I fully understand the angst associated with the air suspension. I'm sorely tempted to give up and switch to the Arnott's Bilstein conversion to be done with this problem once and for all.

kits were shipped yesterday, Singapore is a long way, buy they are on their way to you, don't give up just yet on the air suspension!! Lets see how the refurbishment goes 1st.

best regards

andy

Thanks Andy. Will give it a go.....

Btw, do you actually play the bagpipes?

hee, hee, yes

this is the pipe band i play in

www.maybolepipeband.com

andy

Nice.

My XJ VDP 2004 has the leveling problem. The rear over inflated a couple week ago, now it is really low. I have air suspension fault (amber) and car too low warning (red). Just before the warning, I drove on rough road and potholes in Washington DC and I heard clonking noise from the front left of the car. About a month ago I found about a pint of water on the bottom of the trunk.
Thank you for the info. I will visually check the leveling block valve connectors and electrical components.

Outstanding, Andy! Do you have YouTube video or any audio samples we could listen to? I could only find sheet music on the band's website.

Cheers,

Don

we don't have anything official, I'm sure there will be some clips but i couldn't put you through that pain don!!

andy