I just was looking to see if www.canOBD2.com had come up with more info (should be availible this week) on P0121 which I may have already fixed. On the far right of the features line you will see "REPAIR SOLUTIONS." I put in my car's info and found that the are several service bulletins out for Jags like mine. Some of the bulletins cover what to do about P1254, Throttle valve spring problem; P0491, Secondary air injection system, bank 1; and P0492, Secondary air injection system, bank 2

You can get code defintions there and see where your plug is for the code readers and see about recalls for any car, OBD1 or 2.