For 1990-2009 cars

The steering wheel control switches duplicate the function of the primary controls of the associated component, through a network of multiple momentary contact switches and a series of resistors. The body control module (BCM) supplies voltage to the switches and monitors the return signal. When a switch is pressed, a specific voltage drops across a resistor unique to the switch. The BCM identifies the switch selected and sends a serial data message to the component being controlled by the switch.

This section is intended to diagnosis the circuits between the BCM and the steering wheel control switches. If the primary control for the device is inoperative, refer to the appropriate section of the component the steering wheel control switch is used for.