Powertrain Control Module
NOTE:
On some vehicles, if Powertrain Control Module (PCM) is unable to communicate with Vehicle Theft Deterrent (VTD) system after vehicle has started, PCM will consider VTD system to be malfunctioning. PCM will enter a fail enable state and will command SECURITY indicator to illuminate. When PCM is in a fail enable state vehicle will not stall or stop running. If PCM is in a fail enable state when ignition is switched OFF, PCM will remain fail enabled until communication with VTD system has been restored. When PCM is in a fail enable state VTD system is not active and vehicle will start. This feature is not available on all GM vehicle lines.
PCM verifies that password received from theft deterrent control module via class 2 serial data circuit is correct. PCM can learn only one enable password. If enable password is correct, PCM enables starting and fuel delivery systems.
PCM disables starting and fuel delivery systems if: enable password is incorrect, system disable password is sent by theft deterrent control module, no passwords are received or there is no communication with theft deterrent control module.