www.jec.org.uk

Hi I have a 1996 4 ltr xk8 with 58000 miles .a great car but suddenly the cruise control isnt working properly.i put the control on ok and then after a while it suddenly switches off and a yellow "engine fault" light comes on.the car continues to drive ok and when the ignition is switched off the alarm resets and all is well till the next time i put on cruise control.there is no set time interval and it seems competely random!

thanks for any suggestions.Les

A bit of a stab in the dark but the brake lamp switches are a weak point on the XK8 and correct operation of these switches is necessary for the cruise control to work. A failing switch or its wiring could give rise to erratic cruise control issues. A diagnostics session either with Jaguar diagnostics or the Autologic equivalent modules would help to solve the issue. Mike.

The good news is that when the fault occurs, it lights up the Malfunction Indicator Light (MIL). That means that there will be one or more specific fault codes recorded and they will give a useful guide to identifying the cause.

The less good news is that the owners of very early XK8s seem to have difficulty in getting a diagnostic scanner to connect with the car. The best approach would be to try and identify an independent Jaguar specialist who has the original workshop scanner that Jaguar used at the time.

As well as the electronic part of the cruise control system, the early models also incorporated a vacuum bellows. Let's not go into the details of how it works (unless you want to!), but if there is a vacuum leak between the bellows and the inlet manifold where the vacuum originates, the bellows will expand and trip the cruise control. As this is a mechanical system it does not generate electronic fault codes directly, so is probably less likely to be your problem at this time , but bear it in mind.

Thanks both.food for thought .i will see if i can get a diagnostic check done and report back.thanks again