2004 XJ8 air Suspension too low
 

I now a lot had been posted about air suspension problems with the XJ350. I think I've read most of it but need help if someone has any suggestion.
Vanden Plas 2004 XJ8 air suspension defaulted all of a sudden. Front (R and L) went too low, rear jacked up like crazy.
-1-
Disconnected battery 15 minutes, reconnected not change.
-2-
Disconnected air lines from the rear shocks, they went down. Disconnected batery for 15 minutes. Reconnected and started car. All shocks stayed down.
-3-
Disconnected battery, removed and rebuilded pump, tested ok, pump back in car, battery reconnect. Car stay low, pump not activated. Tested fuse = ok, replaced relay just in case. Disconnected battery for 15 minutes. Reconnected, open and close driver door, car in drive then park. Pump not activated. Jumped terminal 3 and 5 at relay pump started, I let it work for 2 minutes. Let the car run at iddle for 15 minutes. No change suspension too low. Pump never started by itself.
-4-
Had the codes read and reset. Had about 6 codes, including defaulting level sensors (funny they all were defectives at the same time !) and relay .
(probably when I removed it to jumb 3 and 5)
No change car still low on bumps.
-5-
Check pression through the diag tool. 17.2 bars, removed pression sensor at the air rail Under the spare, reading is now 0, still no air compressor starting.
-6-
Disconnected battery
Replaced air compressor with a used one tested ok on another donnor car.
Reconnected battery, started car. No change, compressor does not start
-7-
Still no change.
-8-
Disconnected battery, replaced Wabco ECU unit (from a donor car with working air suspension. It is located Under the rear seat on right.
Tried the trick to discharge capacitor but touching negative cable with the positive of the battery. Reconnected battery.
Still no compressor starting and car suspension on bumbs.
-8-
Drove the car around the block (I cannot even fully turn because tires rubs againts fenders) and waited 15 minutes. No change
-9-
I have the full detailed wiring diagram and I think I understand the system but still cannot figure out what is wrong. I have a friend that have an European car garage and he is out of ideas as well . I am cold about going to the dealer, just for towing the car and dealer at 150 $ an hour , will cost me 500 $ maybe for nothing. I am so sad to let go my air ride and now considering Arnott springs but does not like the idea


ANY HELP OR SUGGESTION WOULD BE VERY APPRECIATED.

I don't see any checks on the height sensors in your list. A sudden failure like that indicates it is not the compressor, as these tend to fail gradually. The compressor is there to keep the reservoir charged up. so if the compressor doesn't try to do this indicates maybe the air pressure sensor for the reservoir is defective

Did you have any "event" of any kind shortly before the failure ?

Are you getting the "suspension too low" message on the message screen ?

It might help if you tell us what codes you got when you read them.

reply to.
 

Thank you for your help
Yes I have the message air suspension too low on the Dashboard.
Nothing special before failure, car was riding wonderfull.
Here the list of error codes we had before we cleared them
C1893
C1885
C1419
C2302
C1830 relay
B2810 vent solenoid.


After we cleared the codes, we are able to read 17.2 bar after manually starting the air compressor for 2 minutes (jumping 3 and 5 at the relay)
Then we removed the air pressure sensor at the rail, reading went back to zéro.
We were also able to see the reading for all four level sensors.
We changed the compressor to another one also

Guy-Pierre Boucher.
I have read and re-read your list of what you have done. I would have suspected the suspension control unit since all else you seem to have replaced and the pump is not being activated the way it should so its not get an activation signal. However since you say that the ECU was replaced with one from a working suspension that does not "seem" to be the issue. My thought is that the system may be locked for whatever reason and the fact you depressurized it may not have altered that state. Resetting might not even alter it.

I have used the JLR SDD diagnostic tool on my 2005 XJR and it allows me to test and recalibrate my suspension.

If I were in your situation, and not want to go to a dealer, I would purchase the JLR SDD and run a test.

Did you make any changes after installing the "new" ECU? I am not sure if adding a new ECU is simply plug and play. Try putting the original ECU back especially if you made changes after you replaced it.

Thanks so much for the help
Do you know where I can get the JRL SDD connector and software for not too much
I can set up a laptop with old Windows if need be.

Have a look at this item number on Ebay. 141693576861

This is the exact one that I purchased. I run it on an old Windows XP laptop.

Due to lack of time and needed'the car
Sent it to dealer
Changed valve block, pump started
Replaced 3 of the 4 level sensors car raised
Calibrated suspension using SDD
Road tested ok 8 hrs labor they accepted to use the parts I brought them (from ã donor car)
I Will order the JLR SDD v130 kit so next'time I can diagnose DIY

Must be good to have the car back on the road!