I just wanted to share the fix for a problem on my 2001 XK8:
Symptoms in order of occurrence:
1. Cruise control will not engage.
2. Red light on cruise control arm switch is extinguished.
3. Orange advisory light illuminated on dash with "FAILSAFE ENGINE MODE" and "CHECK REAR LIGHTS" messages.
4. No performance degradion occurs.
5. All returns to normal when engine is turned off then back on.
6. No codes are present with code reader.

This problem happened almost every time I drove the car.

Root cause: Faulty brake pedal switch

Replacement switch cost $150.

Replacement involved removal of driver's seat and placing my head under the brake pedal pivot such that I could see the forward attachment hold through the footwell. With the assistance of my wife, I was able to engage the studs on the switch assembly into the holes in the footwell. My wife then installed one of the nuts on one of the studs to hold the switch in place. I then finished the attachment and connected the electrical connector. It was especially helpful to move the black insulation out of the way in the pedal area to allow me to see the attachment hole.

Removal took about 2 minutes. Installation took about an hour, including seat removal and installation.

Problem solved!

I hope this helps someone with the same problem. Also, there Are some photos on the Internet that helps to understand this process.

 

Good work.

A handy guy could just replace the micro switches inside the brake switch housing and save some money.

 

I got these warnings this morning on the "Drama Queen". I'll report back with the fix.
Thanks for your post.