Circuit/System Description
WARNING: This page is about a different car, the 2008 Suzuki XL7. 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 momentary contact switches and monitors the return signal. Each switch 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 selection and sends a serial data message to the component controlled by the switch activating the feature.