My dad's GF has a 2000 K3500 with a 7.4L and it shuts off 3 seconds after start up. It has 1 code in the PCM...P1632 which is incorrect or no serial data from passlock system. IS there any GM techs on here that can help me with some diagnostics on this?? My Mitchell on-demand has no diagnostics for this system other than a wiring diagram and system (passlock) re-learn. I have checked all connections, power and grounds to the module and sensors.

BTW, I use this truck all the time for towing the Checkmate

TTT

Anyone?
I hate it when I can't fix something..

Have you done the relearn? Is anything binding when turning the ignition? Is the key excessively worn? If you have relearned the passlock, and it's still doing it I would say you probably have a faulty passlock sensor. A faulty BCM is possible but less likely. Good luck!