Circuit/System Description
WARNING: This page is about a different car, the 2008 Pontiac G8. However, it is still accessible from the selected car via links, so may be relevant.
The instrument panel cluster (IPC) supplies a regulated voltage supply to the steering wheel control switches and monitors the return signal. Each switch state is associated with a specific resistance value. When a switch is depressed a specific voltage drop occurs across the resistor unique to that switch. The IPC is able to identify which switch was depressed by recognizing the voltage drop associated with that switch and responds to the selected request.