I have a 1999 XKR with adaptive cruise control with an annoying fault.
If the engine bay gets hot, i.e. stuck in traffic or even in hot sun, the cruise flashes up as unavailable.
Drive for a while and cool it down, restart and the error clears.
Normally it functions perfectly and this has only shown up during this years warm weather.
Does anybody have a suggestion, I'm planning to drive to Marbella soon and it would be nice to have a working cruise if it gets hot!

 

Sometimes the "Cruise Not Available" message is a result of a failing brake pedal switch. When that is the case, folks usually report seeing both "Cruise Not Available" and "Check Taillights" messages on the dash at the same time. That's how it happened in my wife's XK8 last October. A new brake pedal switch fixed the problem....

 

Thanks for the suggestion, but that doesn't explain why a hot engine bay triggers the fault.
I wonder if the cruise uses pneumatics and heat causes an air leak somewhere.

 

There are a number of OBDII codes that will disable the cruise control. The problem code should be stored in memory and should show up on an auto parts store free scan even if the CEL is not on. Be sure to get all the actual codes and post back for further comments.

 

I will plug my scanner in and report back!

 

Does your cruise have electronic or vacuum control ? If vac, it will have a vacuum hose that goes from the actuator on the top of the throttle body to some control valves inside the wheel arch. Another hose goes from there to the rear of the engine also near the throttle body. Check every hose joint, on a warm day they may get loose and leak. I had a bad one where the control valves are connected causing a similar fault.

If its electronic, then I have no idea. Sorry. Good luck with it.

 

sounds likely, I'll have a poke around and see.