Circuit/System Description
WARNING: This page is about a different car, the 2020 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.
The Restraints Control Module sends the BCM a message telling the BCM that the correct Restraints Control Module is present. The message is sent and verified on every cycle of the key. If the BCM receives an incorrect response or no response at all, vehicle starting is disabled.