Steering Wheel Controls System Circuit Description

The Steering Wheel Controls (SWC) consist of a two-wire switching device controlled by the Dash Integration Module (DIM). The two switch units, the LH side steering wheel controls and the RH side steering wheel controls, are connected together in series with a jumper within the steering wheel. The steering wheel control output leads are connected to the DIM through inflatable restraint steering wheel module coil, a two amp fuse, and several connectors.

The DIM applies a known voltage to the two SWC leads CKT 1796 (DK BLU) and CKT 1375 (PPL). Since the circuit is normally-open, no current flows unless a control button is pressed. When a control button is pressed, a circuit is completed through the button switch and one or more resistors. Current begins to flow. Since the resistors are in series, each button activation results in a unique current value. Pressing the first button in the series results in one resistor in the circuit; pressing the last button results in eight resistors in series in the circuit. The DIM senses when each button is pressed and responds by sending a Class 2 message to the appropriate device. The device (the radio and climate controls or cellular telephone) receives the Class 2 message and performs the appropriate function.

If a button becomes stuck or shorted, the function requested by that button is commanded ON for approximately 30 seconds. After any button is pressed or shorted for approximately 30 seconds, the system shuts off and sets an appropriate Diagnostic Trouble code (DTC). The system becomes re-enabled if the fault clears itself (the short is removed, or the button is released).