Circuit/System Description
WARNING: This page is about a different car, the 2008 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.
The instrument panel module (IPM) supplies voltage to the multiple momentary contact switches and monitors the return signal. Each switch is associated to a set resistance value, when pressed a specific voltage drops across the resistors unique to the switch. The IPM identifies the selection, then sends a serial data message to the component controlled by the switch. If equipped with adaptive cruise control the Gap+/Gap- switches are in place of the mute/source switches and are in the same resistor ladder circuit.