Disconnect diagnostics system

Having a lot of trouble with my 1999XK8 restricted performance. It continually goes into restricted performance and after resetting the system runs well in about an hour. My thoughts are I would like to disconnect the diagnostics. What are your thoughts?

When you say resetting the system, do you mean by disconnecting the battery or something else?

I wouldn’t know where to begin trying to disconnect the diagnostics or even if it’s possible. The modules communicate with each other via data buses (SCP and CAN). Have you scanned the car to see if there are any fault codes?


Do you notice if the cruise control stops working and the brake lights are on at the same time? If it does it may be the brake light switch, this is very sensitive and contains two micro switches, the first cuts out the CC and the second operates the brake lights.
I had this happen to my ‘99 XJR

Yes on disconnecting the battery. N the past when this happened I had a good mechanic reasonably priced. He is no longer available. I was hoping to find a way to fix this problem for good. Ithe dealer in the tea ripped me off for big bucks in the past.
Thanks for your input.

So as per Eric question and mine;
Have you had somebody pull codes or have you noticed whether CC is available when restricted performance happens???
Without further information we are scratching around to help here.

I have not yet pulled codes. I seldom ever use the cruise control but the next time I will check that.

I think the problem is resolved. Had all plugs and coil packs replaced. A little expensive but what a great improvement.

Ok. Finally got back to check window problem. Can’t program passenger window. Comes up uneven and jams about half way up. I can get it all the way up if I hand guide back side of window.

Sounds like maybe the window regulator assembly could be gunked up, or is out of adjustment. I haven’t had to mess with the xk8s much yet, but I would guess that would cause issues with teaching it too

I agree with Jason; it is a window regulator problem, not a programing problem.

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