Powertrain Control Module (PCM)/Engine Control Module (ECM)

When the powertrain control module (PCM)/engine control module (ECM) detects that the ignition is being turned ON, the PCM/ECM waits for a release message from the immobilizer control unit. If a release message is not received within a specified time, the PCM/ECM disables the engine. The engine is also disabled if the identification (ID) code transmitted by the immobilizer control unit does not match the code stored in the PCM/ECM's memory. Immobilization remains in effect until the ignition is turned OFF, or until battery power is removed.
To prevent the vehicle from being driven, the PCM/ECM applies the following strategy:
- The ignition module is put in a bypass mode.
- The PCM/ECM will not create an electronic spark timing (EST) output. Therefore, no spark will be generated by the ignition coil.
- The PCM/ECM will not enable the fuel pump.
- The PCM/ECM will not enable the fuel injectors.
- The PCM/ECM sets diagnostic trouble code (DTC) 53.

Serial data communication is transmitted on a single wire between the immobilizer control unit and the PCM/ECM.
During diagnostic procedures or ID code changing, a scan tool is added to the communication system.
A PCM/ECM with an immobilizer control unit is not exchangeable with a PCM/ECM that does not have an immobilizer control unit.