Circuit/System Description
WARNING: This page is about a different car, the 2008 Saturn Outlook, 2008 GMC Acadia, and 2008 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. The steering wheel control switch is a multiplexed momentary contact switch. Each switch state is associated to a set resistance value and when pressed, a specific voltage drops across the resistor unique to that switch. The BCM identifies the switch selection and sends a serial data message to the component controlled by the switch and activates the feature.