^Agreed. But do this process to check for what code it is throwing (not sure, but I think this works for XJ's as well):
Turn the ignition key until the digital odometer displays, repeat three times in succession and then back to "On" (On/Off, On/Off, On/Off, On). At the fourth "On" the odometer will be replaced with codes. If no codes are present then "Done" will appear.
Once you get the code, post it here