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 Steering Control Module (SCM), then provides resistor multiplexed return outputs to the SCM to indicate the selected switch positions. The SCM then sends electronic switch status messages over a Local Interface Network (LIN) data bus to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), and the EMIC relays electronic switch request messages over the Controller Area Network (CAN) data bus to other electronic modules in the vehicle.

If the SCM detects no inputs from the left multi-function switch, it transmits an electronic Signal Not Available (SNA) status message over the LIN data bus. The SNA status signals the EMIC to request other electronic modules to implement a fail-safe mode of operation for the exterior lighting system. The fail-safe mode automatically turns the exterior lighting ON when the ignition switch is in the ON position, and OFF when the ignition switch is in the OFF position.

The hard wired inputs and outputs of the left multi-function switch and SCM may be diagnosed using conventional diagnostic tools and procedures. However, the most reliable, efficient and accurate means to diagnose this component requires the use of a diagnostic scan tool.

Refer to the appropriate diagnostic information.

EXTERIOR LIGHTING

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

• Automatic Headlamps - The optional automatic headlamps feature is requested when the left multifunction switch control knob is rotated to the automatic (AUTO) detent position with the ignition switch in the ON position. The SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic exterior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic exterior lighting switch request message over the CAN data bus to other electronic modules in the vehicle.
• Front Fog Lamps - The optional front fog lamps are requested when the left multi-function switch control knob is pulled outward to the front fog lamps detent position. The SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic exterior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic exterior lighting switch request message over the CAN data bus to other electronic modules in the vehicle. The switch control knob incorporates an internal cam mechanism that will only allow the front fog lamps to be selected while the headlamp ON position is also selected, and will automatically move the control knob to the front fog lamps OFF position when the control knob is rotated to deselect the headlamps.
• Headlamps - The headlamps are requested when the left multi-function switch control knob is rotated to the headlamps ON detent position. The SCM reads the resistor multiplexed input from the left multifunction switch and sends an electronic exterior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic exterior lighting switch request message over the CAN data bus to other electronic modules in the vehicle.
• 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 SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic beam select switch status message over the LIN data bus to the EMIC, which relays an electronic beam select switch request message over the CAN data bus to other electronic modules in the vehicle.
• 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 SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic beam select switch status message over the LIN data bus to the EMIC, which relays an electronic beam select switch request message over the CAN data bus to other electronic modules in the vehicle.
• Park Lamps - The headlamps are requested when the left multi-function switch control knob is rotated to the park lamps ON detent position. The SCM reads the resistor multiplexed input from the left multifunction switch and sends an electronic exterior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic exterior lighting switch request message over the CAN data bus to other electronic modules in the vehicle.
• Rear Fog Lamps - The optional rear fog lamps are requested when the left multi-function switch control knob is pulled outward to the front fog lamps detent position and then rotated to the rear fog lamps detent position. The SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic exterior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic exterior lighting switch request message over the CAN data bus to other electronic modules in the vehicle. The switch control knob incorporates an internal cam mechanism that will only allow the rear fog lamps to be selected while the front fog lamps ON position is also selected, and will automatically move the control knob to the rear fog lamp OFF position when the control knob is pushed in to deselect the front fog lamps.
• 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 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 SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic exterior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic exterior lighting switch request message over the CAN data bus to other electronic modules in the vehicle.

INTERIOR LIGHTING

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

• Interior Lamps Defeat - The interior lamps defeat feature is requested when the left multi-function switch control sleeve is rotated to the interior lamps DEFEAT detent position. The SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic interior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic interior lighting switch request message over the CAN data bus to other electronic modules in the vehicle.
• Interior Lamps On - The interior lamps ON feature is requested when the left multi-function switch control sleeve is rotated to the interior lamps ON detent position. The SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic interior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic interior lighting switch request message over the CAN data bus to other electronic modules in the vehicle.
• Panel Lamps Dimming - The panel lamps dimming function is active only when the left multi-function switch control knob is in any exterior lighting ON position. With the exterior lighting ON, the panel lamps dimming level is requested when the left multi-function switch control sleeve is rotated to any one of five minor detent positions. The SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic interior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic interior lighting switch request message over the CAN data bus to other electronic modules in the vehicle.
• Parade Mode - The PARADE (or funeral) mode is active only when the left multi-function switch control knob is in any exterior lighting ON position. With the exterior lighting ON, the PARADE mode is requested when the left multi-function switch control sleeve is rotated to the PARADE mode detent position. The SCM reads the resistor multiplexed input from the left multi-function switch and sends an electronic interior lighting switch status message over the LIN data bus to the EMIC, which relays an electronic interior lighting switch request message over the CAN data bus to other electronic modules in the vehicle.