Switch, MULTIFUNCTION: Operation

WARNING: This page is about a different car, the 2017 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.

The 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) internal to the switch housing, 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 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 or default mode of operation. For the exterior lighting system, the multi-function switch fail-safe mode automatically selects LOW beams when the headlamps are turned ON. For the wiper system, the multi-function switch fail-safe mode will maintain the last selected wiper system operation for the remainder of the current ignition cycle, after which the wiper system will default to OFF.

Some of the hard wired input and output circuits for the multi-function switch and SCM 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 this component 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 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 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 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 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.
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 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 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 multi-function switch and sends an electronic turn signal switch status message over the LIN data bus to the EMIC, which relays an electronic turn signal switch request message over the CAN data bus to other electronic modules in the vehicle.
Washer Control - The control knob on the end of the multi-function switch control stalk is depressed toward the steering column to the momentary second detent position to activate the washer pump/motor in the WASH mode. The washer pump/motor will continue to operate for as long as the control knob is held in this position. The SCM reads the resistor multiplexed input from the multi-function switch and sends an electronic washer switch status message over the LIN data bus to the EMIC, which relays an electronic washer switch request message over the CAN data bus to other electronic modules in the vehicle.
Wiper Control - The control knob on the end of the multi-function switch control stalk is rotated to one of the two continuous wiper detents, to one of five intermittent wiper detents, or to the OFF position to select the WIPER mode. The SCM reads the input from the multi-function switch and sends electronic wiper switch status messages over the LIN data bus to the EMIC, which relays an electronic wiper switch request message over the CAN data bus to other electronic modules in the vehicle.
Wiper Mist Mode - The control knob on the end of the multi-function switch control stalk is depressed toward the steering column to the momentary first detent position to activate the wiper MIST mode. The wiper motor will continue to operate, one complete cycle at a time, for as long as the control knob is held in this position. The SCM reads the resistor multiplexed input from the multi-function switch and sends an electronic wiper switch status message over the LIN data bus to the EMIC, which relays an electronic wiper switch request message over the CAN data bus to other electronic modules in the vehicle.