Engine Control Module (ECM)
WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
The ECM communicates with the RCDLR over the serial data line. If the RCDLR receives a valid transmitter RF response, the RCDLR will send the fuel enable message to the ECM to enable the starting system. If the RCDLR does not receive a valid response from the transmitter, the RCDLR will send the fuel disable message, indicating to the ECM that vehicle starting should not be allowed. Additionally, if the fuel enable password received by the ECM does match the stored password, vehicle starting will be disabled.