Just bought a pristine low mileage 1996 XJS. I also have a 1995 XJS. The cruise control in the 96 does not operate. I checked the control switch on the console and it is working. The underhood parts all appear OK but as yet I have not tested them. I'm trying to find the ECM for the speed control to switch it out with the 95 in order to test it. The Manual says it's located in the trunk "above the left wheel arch behind the trim". Having some difficulty envisioning where exactly this is--left of the spare tire; behind the spare tire or on the very far left in front of the CD player. Also, is the car vacuum system only for the cruise control or does it operate a lot of other components? Any thought or ideas would be helpful. Thanks Mike

 

I was never able to make my cruise control work on my 96 either. I have tried swapping out the vacuum pump under the hood, no dice.

I tried replacing the cruise control module as well, no dice. That module is indeed on the side of the CD changer, but is it pretty far back, behind the gas cap, almost at the firewall. Take down the carpet trim that boxes that part out and if you angle your head just right, you'll see it. Take note that it's also where you'll find the anti-slosh module, if/when you'll ever need to find that as well.

I've check the diaphragm under the hood as well, rupturing that rubber bellows is usually what causes it to fail.

Keep me posted on your findings. It is entirely plausible that my spare, used module is no good.

 

Vee

Thanks for the helpful info. Will keep you informed.

Mike

 

The seal around the bellows can dry out too.
Clean it off and reseal with high temperature silicone.

 

I'll bet you it's the relief valve. I refuse to have a non-working item in my car and I went through hell getting my cruise to work. The ECM's are pretty darn reliable, the cruise bellows you can test by sucking on the air hose to the bellows, an easy test. But that dump valve is very hard to bench test. One I replaced it, like magic the system came back to life. In talking to my Jag parts guy it is the weak link in the system in the 90's cars besides the bellows. The dump valve is the same on the XJ6 so there are plenty around.