Audio System Interface
WARNING: This page is about a different car, the 2018 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
When the OnStar® requires audio output, a serial data message is sent to the audio system to mute all radio functions and transmit OnStar® originated audio. The OnStar® audio is transmitted to the vehicle audio system by the Ethernet and GMLAN circuits.
The audio system will mute and an audible ring will be heard though the speakers if the vehicle receives a call with the radio ON.
On some vehicles, the HVAC blower speed may be reduced when the OnStar® system is active to aid in reducing interior noise. When the system is no longer active, the blower speed will return to its previous setting.