Had a bit of a problem over the weekend with my 2000 XK8 (this car gets driven based on weather, and we've had a lot of rain and heat/humidity so only a couple of times in the past month - battery is registering normal voltage so I don't think that is the issue). Out for a drive, pulled to a stop (engine running, foot on the brake) and the engine started running rough and these two messages popped up on the display;
ASC NOT AVAILABLE
TRAC NOT AVAILABLE
10 miles from home so I pulled over, shut of the engine for 5 minutes, restarted, no messages, engine running smooth so I drove home. Connected my scanner, and no error codes listed. Chocked it up to "Jaguar electrical weirdness".

The next day, the same thing happened. I had my code reader with me this time and I received the following error code P0121 THROTTLE/PEDAL POSITION SENSOR/SWITCH "A" CIRCUIT RANGE/PERFORMANCE". Shut off the engine for 5 minutes, restarted but this time the check engine light came on. On the way home, the car started running rough again while sitting at a stoplight and the same 2 messages appeared along with FAILSAFE ENGINE MODE. Top speed of 10 MPH is going to get you killed where I live. Managed to limp the last mile home.

2 questions. Is this simply a throttle sensor that can be easily changed out (after disconnecting the battery) or is it an indication of a throttle problem? Is there anything that can be done when the failsafe mode comes on (the manual says don't drive the car but at this point I wonder if this advice is as good as Jaguar's electrical design engineers)?

Many thanks in advance for anyone's guidance.

 

There is a TSB for the throttle position sensor connector for your (and my) model year.

https://www.jaguarforums.com/forum/a...21-flagged.pdf

You should check and at least clean the connections as a starting point.