Left Multifunction Switch - Operation

OPERATION

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

Some of the hard wired inputs and outputs of the BCM and the left multi-function switch unit may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, the most reliable, efficient and accurate means to diagnose the BCM and the left multi-function switch 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:

- Headlamp Beam Selection - The headlamp high beams are selected when the left 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 BCM reads the resistor multiplexed input from the left multi-function switch and provides a hard wired output to control the shutter solenoids in both headlamp units and also sends an electronic beam select switch status message over the CAN data bus to the Instrument Panel Cluster (IPC) to control the high beam indicator.
- Headlamp Delay - The headlamp delay (also known as Follow Me Home) is activated and a 30 second delay interval is selected when the left multi-function switch control stalk is pulled rearward and released within two minutes following the ignition switch being turned to the OFF position. The delay period is extended by another thirty seconds and accumulates with each subsequent pull and release of the control stalk up to a maximum of 210 seconds. The BCM energizes the relays that control the headlamp low beams and the clearance (position) lamps to provide the selected delay interval. The BCM automatically de-energizes the lamps after the selected time interval expires or, immediately, if the control stalk is pulled toward the steering wheel and held for more than two seconds. The BCM also sends the appropriate electronic messages to the IPC over the CAN data bus to control the Follow Me Home indications in the IPC display.
- Headlamp Optical Horn - The headlamp optical horn is selected each time the left multi-function switch control stalk is pulled fully rearward to a momentary position. The headlamp 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 BCM reads the resistor multiplexed input from the left multi-function switch and provides a hard wired output to control the shutter solenoids in both headlamp units and also sends an electronic beam select switch status message over the CAN data bus to the IPC to control the high beam indicator.
- Turn Signal Control - The turn signals are requested when the left 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 left multi-function switch housing through an opening in the side of the clockspring case 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 left 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 BCM reads the resistor multiplexed input from the left multi-function switch and provides a hard wired output to control the appropriate right or left turn signal relay and also sends an electronic turn signal switch status message over the CAN data bus to the IPC to control the turn signal indicators.