Second tab lists the codes, but if you haven't got the repair manual (£16 on CD from the JDHT) it might be better to hang back from leaping in and replacing the pot.
You might find the (free) book here useful, as well. It doesn't cover workshop manual stuff but there's lots of good info, wrinkles and (dare I write this without getting moderated?) alternative ways of fixing things! http://www.jag-lovers.org/xj-s/book/