Steering Wheel Controls
WARNING: This page is about a different car, the 2008 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.
Some audio functions are available using the steering wheel controls. The steering wheel controls consist of multiple momentary contact switches that connect a series of resistors. When a steering wheel control switch is pressed, a voltage drop occurs in the resistor network, which produces a specific voltage unique to the switch selected. This specific voltage allows the radio (U2R or U2S) or CD changer (U2V or U2X) to identify which switch has been pressed.
The radio or CD changer supplies voltage to the steering wheel controls via the remote radio control supply voltage. The specific voltage signal is returned on the steering wheel controls signals circuit.