I own a XJ40 but a friend of mine just called with a issue and I am tryiny to help her over the phone> My question is does the 1990 XJS V12 utilize the same type of system for the self leveling and brake sysytem with hydrulic system mineral oil as my 89 XJ40?

 

No, the XJS never had a self leveling system.

 

Is it a 2 door XJS or a 4 door XJ12?

 

Ken its a 2 door XJS,
her brakes went out and I didn't know if she had the same hydrulic system I have on my 89 XJ40 to for brake pressure. a auto shop ( knows nothing about jags ) says he thinks its a electrical problem? that stump me on any idea what they might be talking about!

 

Normal brake fluid. Mid year, 1989, Jaguar fitted the XJS with ABS brakes. It could be an accumulator if it has ABS. There is also a pressure switch on top of the ABS pump or a burned ABS pump. If it's pre-ABS, then it's no more complicated than any other brake system. I know I'm kind of jumping around, let me know if I helped or just muddied the waters.