Hi Guest!
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
Michael J.
Jedi Warrior
Offline
According to Figure 03.1 in XJ Series Sedan 1999 Electrical Guide, the Key Transponder Module located below the "Instrument Pack" has four wires; O color for "OK to Start, Y "Security Acknowledgement" that connect to ECM. Y color wire tees to Body Processor Module to area on wire diagram labeled "Engine Cranking Control". SO and SU wires also go th the Body Processor Module. Car was running and abruptly shut off. Turns over but will not start. Friend had this problem and it was a problem with his key. He used his spare (these cars are programmed to accept two key chips) and his started. I have just over 140,000 on the OD. I swapped out ECM with one removed from this same car and sent to Jacksonville, FLA for testing and repair. There has to be some part of key code recognition in the ECM or car would start with any ECM. Had to bring car and ECM to Jag Dealer to have replacement ECM programmed. Car will not start with this ECM either. How do I rule out Key Transponder Module? can voltage me measured at O "OK to Start" wire? Or at "Security Acknowledge" Y wire? 