I just bought a 2004 XJ8 with 119,000 on it and the air suspension fault light is coming on intermittently. I've read about this potentially being the #4 relay in the fuse box but am not sure how to check the relay. I also want to describe the car's behavior and see if anyone has any suggestions on next diagnostic steps. So far I've tried using a bluetooth OBDII reader and Torque on my phone but that does not show any air suspension related codes even when the light is on.

The light will turn on after the car has been on for between 2-10 minutes and usually when I either go over a small patch of rough road or if I hit the brakes somewhat hard. The car sits level, the ride is not different whether the light is on or off and it is extremely smooth. Even roads in the process of being resurfaced result in almost no feedback or noticeable harshness at reasonable speeds.

The light will come on, stay on until the car has been parked and off for about 45 minutes to an hour and will go away after it is started again. Comes on faster when it's below 70 outside but will also come on if I hit the road imperfection or brake hard early into the drive. If it makes it past 10 minutes the light won't go on even after hitting a bump, speed bump or some hard braking.

Any help is greatly appreciated.

-Phil

 

Hi Phil,
My 06 SV8 has similar symptoms with the air suspension fault message but ride height within spec. I've read that if the compressor does not reach a specified pressure in 5 minutes it will trigger that message, but the pressure may be adequate for driving.
I just went through the electrical guide and found R1 in the front power distribution fuse box listed as the air suspension relay - it's the square relay on the inboard side of the box and toward the front of the car in the diagram. The R1 relay in mine did not have a cover on it, so I changed it for the relay in R5 (which the guide said is the EMS control relay for diesel engines) and I put the coverless relay in R3 which was empty and which the guide says is for the left hand windshield heater. I haven't driven it yet to see if it made a difference as I am in the middle of replacing the stabilizer (sway) bar bushings.

BTW, is there a diagram on this site that shows the power distribution boxes and identifies each relay and fuse? I had to search through the electrical guide text for R1 and got many variarions of CR1* before I finally got to the correct function description.

 

It sounds to me like you have a tiny leak somewhere in the system and the air compressor is having to work harder to keep everything filled properly. In time, if this is not addressed, your compressor will require a rebuild. Your symptoms may get worse as the weather gets colder.

I'm sure others will chime in with more advice, but the first thing I would do is check the air hoses going into the top of each shock. Spray some soapy water and if you see little bubbles, there's air escaping. If not, then I would try swapping in a new relay and fuses. If that doesn't do it, then there's an entire myriad of things to check and/or replace, which is why I just got rid of the air suspension system all together. No more headaches.

 

Hi Phil,

Welcome to the Jaguar Forums! It's great to have you with us.

The reason your OBDII scanner is not helping is because it can only read the generic Powertrain codes with a "P" prefix. The air suspension-related codes are mostly Chassis codes with a "C" prefix, and they are proprietary to Jaguar, so to read them requires a dealer-level system or a high-end third-party system like AutoEnginuity with the Jaguar extension. There is a new affordable scanner from iCarsoft that is specifically for Jaguars, but early reviews on this forum were mixed, so I do not yet know if it can be recommended.

Based on your symptoms, it's possible you have a slow leak, so follow XJ8JR's advice about spritzing air hose connections with soapy water to watch for bubbles that indicate a leak. Just take care to avoid wetting any electrical connectors, including the ones for the CATS solenoids on the tops of the air spring/shock absorber units, and the pressure sensor on the valve block in the trunk under the spare tire (that's also where the air reservoir is). Repairing air leaks at the hose fittings is usually easy, though ideally you should use a new brass compression ring or "olive."

At 11 years old and 119K miles, I think I can state with certainty that part of your car's problem is a worn piston ring seal in the air compressor. As Phil Warner mentioned, the system fault can be triggered if the compressor fails to fully pressurize the system in an alloted time period. Replacing the seal is not difficult, and the new seal is very affordable from our forum member bagpipingandy.com. I also replaced the dessicant beads in our air dryer, but most owners won't bother. Here are links to photos showing how the piston ring is replaced:

http://www.jag-lovers.org/snaps/snap...?id=1392905469
http://www.jag-lovers.org/snaps/snap...?id=1392845191
http://www.jag-lovers.org/snaps/snap...?id=1392839130
http://www.jag-lovers.org/snaps/snap...?id=1392825133
http://www.jag-lovers.org/snaps/snap...?id=1392814031
http://www.jag-lovers.org/snaps/snap...?id=1392752921
http://www.jag-lovers.org/snaps/snap...?id=1392738954


And since we're a friendly group, please visit the https://www.jaguarforums.com/forum/n...-intro-must-5/ and post an introduction so we can learn something about you and your Jag and give you a proper welcome.

Cheers,

Don