Combination Switch: Description and Operation

The multi-function switch (3) is located on the steering column, just below the steering wheel. The only visible components of the multi-function switch are the control stalk (2) and control knob (1) that extend through the steering column shrouds on the left side of the column, and the hazard warning push button (4) that extends through the shroud on the top of the column. The remainder of the switch including its mounting provisions, its electrical connection, and the turn signal cancel actuator (5) are concealed beneath the shrouds.

The switch housing and controls are constructed of molded black plastic. Each of the switch controls has white International Control and Display Symbol graphics applied to it, which clearly identify its many functions. Three integral locating posts on the switch housing, one on the top and two on the bottom, slide into channels in a receptacle on the left side of the multi-function switch mounting housing near the top of the steering column to ensure proper positioning of the switch. Then two screws secure the switch to the mounting housing. A single integral connector receptacle containing four terminal pins on the back of the switch housing connects the switch to the vehicle electrical system through a dedicated take out and connector of the instrument panel wire harness.

The multi-function switch provides the vehicle operator with a control interface for the following functions:
- Front Washer Control - The multi-function switch control knob provides a momentary position for front washer system operation.
- Front Wiper Control - The multi-function switch control knob provides two continuous front wipe switch positions, low speed or high speed; and, an intermittent front wipe mode with five delay interval positions.
- Hazard Warning Control - The multi-function switch hazard warning push button provides two detent positions (On and Off) to control the hazard warning lamps.
- Headlamp Beam Selection - The multi-function switch control stalk provides detent switching for selection of the headlamp high or low beams. There is also an intermediate momentary position that allows the headlamp high beam circuits to be momentarily flashed to provide an optical horn feature (sometimes referred to as flash-to-pass) as an optical signalling device.
- Turn Signal Control - The multi-function switch control stalk provides momentary non-detent (lane change) switching or detent switching with automatic cancellation for both the left and right turn signal lamps.

The multi-function switch cannot be adjusted or repaired. If any function of the switch is faulty, or if the switch is damaged, the entire switch must be replaced as a unit.

The multi-function switch uses resistor multiplexing to control the many functions and features it provides using only three hard wired output circuits. The switch receives a clean ground from the ElectroMechanical Instrument Cluster (EMIC) (also sometimes referred to as the Cab Control Node/CCN) on a multi-function switch return circuit. It then provides outputs to the EMIC on a wash/beam select switch signal circuit to control front washer and headlamp beam selection, on an intermittent wiper switch signal circuit to control front wipers, and on a turn lamps switch signal circuit to control turn signal and hazard warning functions.

The multi-function switch operates as follows:
- Front Washer Control - The control knob on the end of the multi-function switch control stalk is depressed towards the steering column to momentarily activate the washer pump in the front washer mode. The washer pump will continue to operate in the front washer mode until the control knob is released. The multi-function switch provides an output to the EMIC, and the EMIC responds by sending electronic front washer switch status messages to the Front Control Module (FCM) over the Controller Area Network (CAN) data bus. The FCM responds by energizing or de-energizing the washer pump in the front washer mode.
- Front Wiper Control - The control knob on the end of the multi-function switch control stalk is rotated to one of the continuous front wiper detents, to one of five intermittent wiper detents, or to the Off position to select the front wiper mode. The multi-function switch provides an output to the EMIC, and the EMIC responds by sending electronic front wiper switch status messages to the FCM over the CAN data bus. The FCM responds by energizing or de-energizing the wiper on/off and high/low relays in the Power Distribution Center (PDC) for front wiper system control.
- Hazard Warning Control - The hazard warning push button of the multi-function switch is depressed to activate the hazard warning system, and depressed again to turn the system Off. When the push button is actuated, the multi-function switch provides an output to the EMIC, and the EMIC responds by sending electronic hazard switch status messages to the FCM over the CAN data bus. The FCM then energizes and flashes or de-energizes both the left and right turn signal circuits to provide the visual hazard warning.
- Headlamp Beam Selection - The control stalk of the multi-function switch is pulled towards the steering wheel past a detent to actuate the integral beam select switch circuitry, or to an intermediate, momentary position before the detent to actuate the optical horn feature. Each time the control stalk is actuated to a detent position, the opposite headlamp beam from what is currently selected will be energized. Each time the control stalk is actuated to the momentary position with the headlamps turned off, the headlamp high beams will be illuminated for as long as the control stalk is held in this position. The multi-function switch provides an output to the EMIC, and the EMIC responds by sending electronic beam select switch status messages to the FCM over the CAN data bus. The FCM energizes or de-energizes the selected low or high beam circuits.
- Turn Signal Control - The control stalk of the multi-function switch is moved upward to activate the right turn signal circuitry, and, downward to activate the left turn signal circuitry. The turn signal switch has a detent position in each direction that provides turn signals with automatic cancellation, and an intermediate, momentary position in each direction that provides turn signals only until the control stalk is released. When the control stalk is moved to a detent turn signal switch position, the cancel actuator extends toward the center of the steering column. A turn signal cancel cam that is integral to the clockspring 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 two 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. When a turn signal is activated, the multifunction switch provides an output to the EMIC, and the EMIC responds by sending electronic turn signal switch status messages to the FCM over the CAN data bus. The FCM energizes and flashes or de-energizes the selected left or right turn signal circuits.

The multi-function switch can be diagnosed using conventional diagnostic tools and methods. However, proper testing of the multiplexed inputs to the EMIC requires the use of a diagnostic scan tool.