It seems that your temperature sensor/circuit was/is sensed by the
computer to have/had an issue.

The sensor is a two wire do-dad up close to the thermostat housing.
That is of course if you are Talking about a Jaguar XJ40 and not some
Rover. ;-)

Clean the wire connection and also the single wired temp sensor close
by. Reset your computer (Make note of your radio security code and
disconnect your battery for about 30 seconds) and see if the code
reappears.  If it does then your sensor may be out of calibration and
should be replaced.

Cheers,
B.D.