Circuit/System Description
WARNING: This page is about a different car, the 2008 Pontiac Torrent and 2008 Chevrolet Equinox. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) supplies voltage to the audio steering wheel control momentary contact switches and monitors the return signal. Each switch is associated to a set resistance value. When a switch is pressed a specific voltage drops across the resistor unique to the switch. The BCM identifies the selection and sends a serial data message to the component controlled by the switch, activating the switch selection