Circuit/System Description
WARNING: This page is about a different car, the 2010 Chevrolet Aveo. However, it is still accessible from the selected car via links, so may be relevant.
The Onstar module communicates with the RKE module through the IPC. The IPC is the gateway connecting the Onstar and RKE. Using data link circuit the Onstar module can send a signal to RKE in order to control the door lock/unlock.