Circuit/System Description
WARNING: This page is about a different car, the 2013 GMC Acadia, 2013 Chevrolet Traverse, and 2013 Buick Enclave. However, it is still accessible from the selected car via links, so may be relevant.
When an OnStar® keypress is made, a serial data message is sent to the audio system to mute all radio functions and output OnStar® originated audio. After the audio system is muted, the vehicle communication interface control module transmits signals to the audio system on the audio signal and audio common circuits.