GM Service Manual Online
For 1990-2009 cars only

The Body Control Module (BCM) (2) is the PASS-Key II® controller and performs the ignition key resistance identification and communication of the pass or fail condition to the Powertrain Control Module (PCM). Security is provided by determining if a valid ignition key (1) has been used in an attempt to start the engine and if so, communicating a fuel enable and starter enable message to the (PCM).