We are having a bit of a problem with our 2002 XKR. For the first 20 minutes or so everything is fine. Cruise control works fine, no error messages. Eventually the cruise control won't work, but the cruise control light is still illuminated. That goes on for 10 minutes. Then the cruise control light goes off and "check rear lights" and "failsafe mode" is displayed. Cruise control doesn't work at all. However, the car still runs fine. If you then pull over, shut off the car then restart it and continue on the cruise control won't immediately work, but after about 5 minutes it starts to work. After that the whole process repeats over.

Using a generic OBDII code reader is pulls code P1642.

I'm leaning toward the brake pedal considering cruise gets turned off like someone tapped the break (but hasn't) and its also displaying that rear light message. Any ideas?

 

Here is the readout of the P1642 code

Default Action:
P1642 CAN (controller area network) circuit malfunction Ignition ON > 5 seconds
When fault is detected, ECM (electronic control module):– Limits throttle to approximately 30%
– Inhibits cruise control (All CAN data unavailable)

Possible Causes:
CAN short circuit fault
Control module failure – check for additional flagged DTC(s) (diagnostic trouble code(s)) to locate control module source

 

I think that your brake switch is going bad. The brake light error and no cruise both run off the switch. I see the code you are getting but you said that you are not getting a limited throttle. There are a few threads and I think Rev Sam did a video on the replacement.

 

The last time the brake switch went out on out 1998 XJ8 we had cruise control issues, but I don't think we got the rear light message. The cruise is acting like someone touched the brake, when it hasn't been touched. Correct, but I also read that with a generic scanner that code sometimes doesn't mean much. No vid necessary, easy enough to do.

 

I get this too, although I don't know about the cruise since I never use it.

Like yours, the performance is not restricted. I am going to go the Rev Sam route and fix the brake switch, hopefully curing the problems...

I am going to be very interested in what you do!

 

Brake switch...

 

Yeah, that was my first thought and seems to be the general consensus. Its on my to do list.

 

The brake switch is sort of spendy.

A handy guy could easily remove the brake switch assembly and just replace the two micro switches and save a lot of money. They could not be easier to get to and I believe they are rather common. There is a thread here on the Forum in that regard.