I have a Jag XJ8 (52 plate). For a number of months there have been false warnings flashing up and going away. Like ABS warning one minte, TRAC warning next, rear light warning next, RANGE ERROR (showing empty even when full) next, doors wont respond to key fob one minute then will the next; boot won't open with key fob but will manually. Radio won't go off when you close down engine. All different but clearly an electrical fault. Now it won't start. Jaguar Stratstone have done an initial check but want to spend many more hours (gulp!) on it, does anyone have any ideas please?

Alan Hunter, April 2010

Has the alternator output and battery condition been checked? Also make sure all earth cables/connections are in good condition.

crank, April 2010

I just guess - I know nothing of motor vehicle electrics...

The warning lights in the car will probably be driven from a microprocessor running a small s/w programme. It may be possible that the s/w has a bug in it but the symptoms you report are not consistent with a s/w problem - too many things failing and - if it was a s/w issue - then other cars would also suffer and the manufacturer and the dealer would know about it.

Electronic components generally fail or work - they usually only behave intermittently when there's a poor connection. Continuing the guessing game your car may well have a poor or loose connection in the area of the small computer that runs the warning lights and dashboard etc - the vibration of motion makes the fault come and go - I would suspect a defective connector plug/socket or a dry joint. Very probably in the dashboard cluster circuit board.

Tapping with a wooden spoon in an attempt to bring the fault on may help diagnosis.

Good luck...

Peccavi, April 2010