Switch, MULTIFUNCTION: Operation

The multi-function switch uses resistor multiplexing to control the many functions and features it provides using a minimal number of hardwired circuits. The switch receives clean grounds from the Steering Column Control Module (SCCM), then provides resistor multiplexed return outputs to the SCM to indicate the selected switch positions. The SCCM then sends electronic switch status  messages over the Controller Area Network (CAN) data bus to the Body Control Module (BCM) and other electronic modules in the vehicle.

If the SCCM detects no inputs from the multi-function switch, it transmits an electronic Signal Not Available (SNA)  status message over the CAN data bus. The SNA status signals the other electronic modules to implement a fail-safe or default mode of operation. For the exterior lighting system, the multi-function switch fail-safe mode automatically selects LOW beams when the headlights are turned ON. For the wiper system, the multi-function switch fail-safe mode will maintain the last selected wiper system mode of operation for the remainder of the current ignition cycle, after which the wiper system will default to OFF.

The hardwired inputs and outputs of the SCCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the multi-function switch or the electronic controls and communication between other modules and devices that provide some features of the lighting or wiper and washer systems. The most reliable, efficient and accurate means to diagnose the multi-function switch or the electronic controls and communication related to right multi-function switch operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.

Following are descriptions of how the multi-function switch is operated to control the functions and features it provides:

• Headlight Beam Selection  - The headlight high beams are selected when the multi-function switch control stalk is pushed forward to the high beam selection detent position. The low beams are selected when the control stalk is pulled rearward to the low beam selection detent position. The SCCM reads the resistor multiplexed input from the multi-function switch and sends an electronic beam select switch status  message over the CAN data bus to the BCM and to other electronic modules in the vehicle.
• Headlight Optical Horn  - The headlight optical horn is selected each time the multi-function switch control stalk is pulled fully rearward to a momentary position. The headlight HIGH beams will remain illuminated for as long as the control stalk is held in this momentary position and the LOW beams will be restored when the control stalk is released. The SCM reads the resistor multiplexed input from the multi-function switch and sends an electronic beam select switch status  message over the CAN data bus to the BCM and to other electronic modules in the vehicle.
• Turn Signal Control  - The turn signals are requested when the multi-function switch control stalk is moved downward (LEFT signal) or upward (RIGHT signal). The control stalk has a detent position in each direction that provides turn signals with automatic cancellation, and an intermediate, momentary position in each direction that automatically provides three turn signal blinks as a LANE CHANGE feature when the control stalk is tapped or will energize the turn signals for as long as the control stalk is held in the momentary position. When the control stalk is moved to a detent turn signal switch position, a cancel actuator extends from the multi-function switch through the SCCM mounting housing toward the center of the steering column. A turn signal cancel cam that is integral to the clockspring rotor rotates with the steering wheel and the cam lobes contact the cancel actuator when it is extended from the multi-function switch. When the steering wheel is rotated during a turning maneuver, one of the turn signal cancel cam lobes will contact the turn signal cancel actuator. The cancel actuator latches against the cancel cam rotation in the direction opposite that which is signaled. If the LEFT turn signal detent is selected, the lobes of the cancel cam will ratchet past the cancel actuator when the steering wheel is rotated to the left, but will unlatch the cancel actuator as the steering wheel rotates to the right and returns to center, which will cancel the turn signal event and release the control stalk from the detent so it returns to the neutral OFF position. The SCCM reads the resistor multiplexed input from the multi-function switch and sends an electronic turn signal switch status  message over the CAN data bus to the BCM and to other electronic modules in the vehicle.