There are no "generic" codes for the radio. If it's an XJ6 '88-'95 there is a small white sticker under the bonnet on the top left corner by the hood spring pin (if it hasn't fallen off or been weathered) with a bar code on it. The last 4 digits are the radio code. If this isn't there then you need to remove the radio and right down the serial number found on the bottom and call a Jaguar dealer for the code
hay88, April 2010