2004 XJ8
I know there are lots of posts on this and I think I read them all but have not found any answers.
1st I will tell what I did.
Replaced all 4 air shocks with new Arnott
Replaced compressor with new Dorman (Other 1 was only 2 years old)
Replaced front height sensor
Bought isoft code reader for jags and cleared all codes afterward
While I was at it I replaced all suspension arms and tie rods in the rear end.
All this was done in the last month.

I still get the reservoir plausibility error code.
However it will only come on at speeds above 25 mph.
I can drive all day without the light or code if I keep it below 25 mph
As usual after 20 minutes of no driving the light resets and will not come on until I drive above 25
The compressor came on last night as soon as I started the car and again about 3 minutes later at 10 mph I believe because of about a 15 degree ambient temp drop.
The car does not sink over 3 days sitting and the compressor runs rarely I'm guessing because of the new shocks.

If anybody has any ideas I would greatly appreciate them.
Thanks,
Dave

 

By the way the car drives perfectly at all speeds.
The suspension works great
Dave]

 

The c2303 code can be notoriously spurious!

I have had it myself.

I suspect it could be related to the Dorman compressor.

How does the spec for it compare with the Wabco unit?

You could try changing back to the pump that you removed,if it was only two years old.

Just a few thoughts.

 

I was thinking the same thing before I drove it today. I figured out the isoft reader gives real time data so I watched it and drove the car. At 25mph the reader said the compressor came on. I could not hear it maybe because of road noise or maybe because it didn't come on. 10 seconds later the air suspension light came on and the code reader said compressor off. I drove it for 20 miles on highway and local streets. The compressor did not come back on. I would have thought it should have. When I got home I figured the car would be lower do to know compressed air generated. It was perfect ride height. Do you still think it might be the compressor? I have heard it run at start up and low speeds and it doesn't throw a light. It's the 25 mph mark that the problem occurs.

 

I think you need to satisfy yourself that the dorman pump can pressurise the

ballast tank to the right pressure in the alloted time if not then the code will be set.

I believe the tank runs at 200+ psi.

 

I agree. I have been running the real time data and the compressor will not run for more than 20 seconds. Usually the light and code will come on at 15 -20 seconds in. I never drive over 25 without it coming on. I'm going to check the pressure 1st and then if it's not correct put the old compressor back on Sat. I'll let you know what happens. Thanks for your ideas.

 

I used to have the suspension failure issue. Mine as a leak in one shock. Seemed fine sitting. Maybe would drop an inch or so. Finally replaced with another and all is good.
The compressor would run a long time. Over a minute. Then the light and it would shut off.

 

The shocks and compressor are all new.The compressor runs after 25 mph but no more than 30 seconds and then the light comes on. I can't figure out if it's being told to shut down or if it loses power. I think it is faulting because it isn't running long enough to fill the tank but not sure yet

 

"I can't figure out if it's being told to shut down or if it loses power."

Check/substitute/replace relay R1 in the engine compartment fuse box.

 

You should've installed an Arnott air compressor since the shocks are Arnotts, my opinion

 

I have an arnott compressor. Its the 1 I took out. The relay came in today and Im trying that now. If that doesn't work I am swapping the arnott comp. back in.

 

Ok replaced relay r1. Still get the suspension fault. Swapping out compressor tomorrow

 

rf69,

No offense intended, but I have to take exception with that statement. The original Jaguar equipment includes an air compressor made by Wabco and air springs/shock absorbers made by Bilstein. Jaguar didn't think they had to be the same brand, so why should we? Air compressed by an Arnott compressor is no different than air compressed by a properly-functioning Wabco (Jaguar OE) compressor or a Dorman compressor that can provide sufficient pressure.

Dave,

I would highly recommend that you download and read the Air Suspension and ECATS section of the Dealer Training Manual. It provides the most detailed explanation of the air suspension operation that I'm aware of:

http://www.mediafire.com/file/7rdkgg...on_Section.pdf

Also, if you don't have it, the DTC Summaries Manual is very helpful and can be downloaded here:

https://www.google.com/url?sa=t&rct=...03388427,d.cWw


The behavior of your compressor may be correct. The Air Suspension Control Module (ASM) is programmed to run the compressor for up to 120 seconds at a time when necessary to restore the pressure in the reservoir. There is no temperature sensor on the compressor, so after the compressor is shut off, the ASM will not allow it to run again for about 45 seconds to allow it to cool.

The compressor should run if needed while the transmission is in Park, but once the transmission is in Drive the compressor is prevented from running until the road speed exceeds 25 mph. This is probably one of Jaguar's many noise management strategies. Above 25 mph the sound of the compressor running is masked by road noise.

One possible cause of your symptoms is a problem with the pressure sensor on the valve block near the reservoir (under the spare wheel in the trunk). The reservoir plausibility fault code (C2303) seems to be triggered if the system does not achieve proper air pressure within some programmed length of time. The most common cause seems to be a worn piston ring/seal in the compressor (easily replaced with bagpipingandy's kit). The DTC Summaries Manual gives possible causes of C2303 as a mechanical/pneumatic fault such as a disconnected air pipe or an air leak. But since the ASM relies on the pressure sensor to tell it when the system pressure is correct, it seems possible that your system pressure could be fine, but the ASM doesn't know it due to a fault with the pressure sensor. It would be worth checking and cleaning the electrical connectors for the pressure sensor and valve block.

It might also be worth cleaning the ground points used by the suspension. The ASM ground is under the rear seat on the right hand side near the ASM (some members have reported water in that area due to a clogged sunroof drain). The compressor ground is behind the left headlamp. The air suspension relay is grounded at the point under the front power distribution fuse box. The threaded studs, nuts, star washers and wiring ring terminals are all made of aluminum. Aluminum oxide is a whitish residue that forms in a very thin, nearly invisible layer on the ground components, and it is an electrical insulator so it interferes with electronic signals. Note that the torque spec for the ground nuts is just 6.5 ft. lbs., or just a little more than hand tight. Several members have snapped off a threaded stud by overtightening the nut.

Please keep us informed.

Cheers,

Don

 

Thank you Don!
I'm going to check everything you mentioned before I change out the compressor. It is brand new and I really do not think it's the problem but was out of ideas. I will post details tomorrow. I have heard the battery can play havoc on the system and am going to watch the battery data stream when the compressor kicks on and off. I don't know if it's worth noting or not but the compressor will not turn back on after a fault code no matter how long I drive it. It only runs twice at the most before I get a dash light.
Thanks again,
Dave

 

Our '04 behaves the same way. Once the AIR SUPSENSION FAULT is triggered, the compressor will not run again until I have cleared the DTCs.

If your compressor runs once or twice and the ASF is triggered, either your system is not achieving correct pressure in the alloted time (I'm not sure what the time limit is), or the pressure is good but the ASM doesn't think it is. That's what led me to mention the pressure sensor on the valve block, whose signal the ASM depends on to know when correct pressure has been achieved.

Please keep us informed.

Cheers,

Don

 

Yes but...
I have had an ASF on past winter, with the compressor not succeeding to level the car after two attempts.
But on the following day, without having cleared the ASF code, and igniting the engine again, the compressor started and succeeded levelling the car which, on that time, remained at level on the first attempt...
So it seems that sometimes the leak (compressor or shock, dunno) could be small enough that it may be intermittent or depend on the conditions (maybe the temperature was warmer?)

 

Now that you mention it, I don't think it has been consistent on our car either - sometimes it will recover from ASF. Perhaps it depends on which DTC is causing the ASF?

 

I think I have it fixed. I took the spare out 1st and looked at the valve block and electrical connector. Looks like new. No corrosion on anything. In doing so I bumped the hose going into the air tank and it was totally disconnected. The hose was at the hole and looked fine so if I had not touched it I would have never known. It apparently worked loose over time. I have had the car 5 years and never had this problem. I could have saved myself alot of time, effort and money had I looked there and checked the hoses before. I had no experience with the valve block until today. The suspension then worked great for awhile. I watched the data stream from my code reader and the compressor cycled on and off and would run for about a minute on back roads and then shut off. No code yet. Did this for about 10 miles and was getting giddy at having figured it out. No such luck. I took it on the highway and drove for about 4 miles and the compressor came on for 1 minute and then shut off as the fault lit up. As you know I replaced the compressor. The dorman compressor came with a new brass airline connector and collar. I put the new 1 on the line but the collar has to be in a certain direction and I couldn't remember at the time how I took it off so I put it back on like I thought it should be. (The narrow end goes toward the fitting. I figured this out when I fixed the air tank hose.) I took the hose off the compressor to see if I had it right. I did but I had pushed it to far up the hose so that when I tightened the fitting down it crushed the tip of the hose about 25% causing a 25% restriction in air flow. This then caused the tank not to fill fast enough throwing the same code for another reason. The compressor has only cycled once in 15 miles since I fixed the compressor fitting. I don't think it could get the volume of air it needed at the tank fast enough and that I believe is why it was cycling before. I thought that was normal but after I thought about it with all 4 new shocks it shouldn't use that much air.

What is strange to me is that the car never sagged with the hose off of the air tank. There was no air in the tank at all. The valve block must lock out the tank when a leak occurs.

I hope this helps someone. You guys sure helped me. I sure appreciate it.
Special thanks to you Don.
If you ever make it to St. Louis I owe you a steak dinner.
Thanks,
Dave

 

Dave,
Thank you for the feedback, may help a number of us.
I never thought of such a possible failure at the valve block level.
Good to make a check whenever an ASF comes in!

 

Dave,

Congratulations on your excellent diagnostic work and persistence, and thank you for the detailed report. I agree with paydase that your saga will no doubt help many others in the future. I've added RESOLVED to the thread title so others will know you found the solutions to the issues.

Cheers,

Don