Fix Jaguar XJ8 / x350 Air suspension " pressure relief valve " o-rings oring o-ring

These O-Rings on the brass pressure relief valve can, and will fail over time. My leak was not very obvious, but it was leaking from below the valve, very slowly causing the car to throw the amber "air suspension" warning light and the car would slowly sink down over the course of several days.

It took me QUITE some time to figure this out, as I kept ordering new air shocks, and using the same pressure relief valve when installing the new shock on the drivers' side.

 Eventually, I figured it out and traced the problem to the O-Ring on the valve with soapy dish fluid water in a sprayer. But it was not immediately evident, and the leak must have been very slow.   Only a visual inspection confirmed the o-ring had failed. 

To test your air connections for leaks, just spray all of your connections, and the valve block in the trunk and tank connections and look for bubbles from the soap solution on the connections.   Also remember to spray the shock rubber air bags themselves, from inside the wheel well if you think a specific shock itself is leaking , or you hear air escaping from that side of the car.  If air is leaking from a fitting, you'll see it generate bubbles fairly quickly -- or not, like in my aforementioned case.

The valve block, and air tank under the spare tire in the trunk / boot

The valve block is mounted in the trunk beneath the spare wheel and a sound-deadening foam cover. It shares the same mounting bracket as the air reservoir. The valve block contains five individual solenoid valves, one for each of the four air springs and one for the reservoir. A pressure sensor (made by Denso) is mounted to the valve block manifold. The sensor monitors system pressure and communicates this information to the ASM. Six air hoses or pipes are mounted to the valve block manifold, one for each of the four air springs, one for the reservoir, and one for the air compressor. The air hoses for the front air springs are 6mm and the hoses for the rear air springs are 4mm.

The air hoses are color-coded as follows:

Left Rear air spring: Blue
Left Front air spring: Brown
Right Rear air spring: Red
Right Front air spring: Yellow


Under the control of the ASM, the solenoid valves in the valve block perform the following operations:

• Increase or decrease the pressure in the front air springs as a pair (or individually on early cars with 4 height sensors)

• Increase or decrease the pressure in each individual rear air spring

• Direct air from the compressor to repressurize the reservoir

• Allow air from one or more air spring(s) to be released through the compressor exhaust vent solenoid valve

Jaguar XJ8 / x350 - Replacement O-Ring Information 

Here are the proper sizes for the air shock connection o-ring sizes with photos.

UPDATE 1.22.20 :  The O-Ring size : 6mm ID x 8mm OD x 1.5 mm W .    I ordered 1mm width and it's just not wide enough.  You'll need 1.5 to probably 2mm in width so that the o-ring comes up to the last thread.   The 1mm width o-rings are not correct and in the Jaguar forums someone mentioned  #6 O-Rings (7/16" O.D x 5/16" I.D X 1/16") but those are not right either for the air valve o-rings.  You (may) be able to make Danco #47 o-rings work for you ; those are 11/32" OD x 7/32 I.D. x 1/16".

I found that the 6mm ID 9mm OD x 1.5 mm / 2.0mm o-rings from Ace Hardware worked for me.  So it's 1mm larger than the 8mm OD, but it still worked fine.