Circuit/System Description
WARNING: This page is about a different car, the 2010 Saturn Outlook, 2010 GMC Acadia, 2010 Chevrolet Traverse, and 2010 Buick Enclave. 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 switches and monitors the return signal. Each switch state is associated to a set resistance value and when pressed a specific voltage drop occurs across the resistor unique to the switch. The BCM identifies the switch selection and activates the feature.