Engine Control Module (ECM)
IMPORTANT:
The remote control door lock receiver (RCDLR) is not on the GM LAN high speed bus, therefore the RCDLR and the engine control module (ECM) must use the body control module (BCM) as a gateway in order to communicate.
The ECM communicates with the BCM and the RCDLR over the serial data line. When the RCDLR determines a no start condition, it sends a serial data password to the ECM in order to disable the starting system. If the RCDLR receives a valid key fob radio frequency (RF) transmitted frequency, the RCDLR sends a serial data password to the ECM in order to enable the starting system. The ECM then allows the vehicle to start correctly. If the serial data password from the RCDLR to the ECM is not within the Vehicle Security Status Message, the vehicle will not start. If the ECM does not receive the same password from the RCDLR as the last learned one, the vehicle will not start.