Principles of Operation

Steering Column Switches

Principles of Operation

Ignition Switch

The ignition switch is controlled by the ignition lock cylinder and a key. The ignition lock cylinder and ignition switch are connected mechanically, turning the lock cylinder places the switch into the desired position. The available switch positions are:

- OFF
- ACC
- RUN
- START

When the lock cylinder is turned from the OFF position, the ignition switch provides voltage inputs to the Body Control Module (BCM), the PCM and the Brake Shift Interlock Actuator (BSIA) based on the specific position selected. The ignition switch contains a key-in-ignition input that allows the BCM to detect when the key has been inserted in the ignition, to initiate the module wake up cycle. This information is also used by the BCM for the brake shift interlock system. For information on the brake shift interlock system, refer to Automatic Transaxle/Transmission External Controls Testing and Inspection.

Steering Column Control Module (SCCM)

The SCCM controls various systems and/or features:

- Wiper and washer system; refer to Wipers and Washers Testing and Inspection.
- Exterior lighting; refer to Lighting and Horns Lighting and Horns.
- Interior lighting; refer to Interior Lighting Testing and Inspection.
- Steering wheel audio controls (if equipped); refer to Information and Entertainment Systems Testing and Inspection.
- Steering wheel message center controls (if equipped); refer to Instrumentation, Message Center, and Warning Chimes Testing and Inspection.
- Cruise control; refer to Cruise Control Testing and Inspection.
- Adjustable pedals; refer to Hydraulic Brake Actuation Testing and Inspection.

The SCCM provides a pass-through circuit path for various components and/or features:

- Steering wheel switch illumination
- Driver air bag module
- Horn

The multifunction switch, adjustable pedal switch (if equipped), hazard flasher switch and steering wheel controls (if equipped) provide inputs to the SCCM. Based on inputs from the various switches, the SCCM communicates over the High Speed Controller Area Network (HS-CAN) to control the supporting features.

Multifunction Switch

The multifunction switch is mounted directly to the SCCM and controls the high beam headlamps, flash-to-pass, turn signals and windshield wiper by transferring the driver inputs to the SCCM. The high beam headlamps, flash-to-pass and turn signals are communicated from the SCCM over the HS-CAN. The windshield wiper signals are communicated from the SCCM to the wiper motor internal module over the Local Interconnect Network (LIN). The BCM activates the required components when the correct signal is received from the SCCM.

Adjustable Pedal Switch

The adjustable pedal switch is mounted directly to the SCCM and controls the forward and rearward movement of the accelerator and brake pedals. The adjustable pedal switch functions when the ignition switch is in the OFF, ACC or RUN positions. When the adjustable pedal switch is pressed voltage is connected through the SCCM to the adjustable pedal motor.

Hazard Flasher Switch

The hazard flasher switch is mounted directly to the SCCM and operates when the ignition switch is in any position or when the key is removed. One press of the switch supplies a ground signal through the SCCM to the BCM. When the ground signal is sensed by the BCM, it turns the directional indicators on. A second press of the button releases the ground connection and turns the directional indicators off.

Steering Wheel Switches

The steering wheel switches are mounted directly to the steering wheel and wired to the SCCM. Depending on what features the vehicle is equipped with, the SCCM sends messages via the HS-CAN to the PCM (cruise control), Instrument Panel Cluster (IPC) (message center) and BCM (entertainment system). The BCM receives the SCCM entertainment system messages via the HS-CAN and sends them over the Medium Speed Controller Area Network (MS-CAN), where the messages are received by the applicable entertainment system module(s).

Circuit Deactivation Ignition Module (CDIM)

Vehicles equipped with a 6.7L diesel engine may also be equipped with an extended idle shutdown system. This system is controlled by the PCM and uses several inputs to determine whether or not to shut the engine off. The CDIM disables the ignition switch circuits after the PCM has shut the engine off. For a complete description of the extended idle shutdown system and related components, refer to Computers and Control Systems.

Once the PCM has determined that the engine should be shut down, it sends a message to the IPC along the HS-CAN. The IPC then sends a message to the CDIM along the MS-CAN. Once the CDIM receives the message from the IPC, the CDIM begins a 60 second timer and monitors the MS-CAN for ignition switch position, brake pedal position and engine rpm. If the rpm remains at 0 and both the ignition switch and brake pedal switch remain undisturbed for 60 seconds, all CDIM internal relays open and the vehicle enters into the standard accessory delay. If one or more of the monitored signals changes during the 60 second time period, the CDIM internal relays remain closed, allowing voltage to remain applied to the ignition circuits.

To reactivate the CDIM and ignition circuits after the engine shuts down, the ignition switch must be turned to the OFF position before attempting to start the engine or before the ignition switch is turned to any other position.

If the vehicle is getting the extended idle shut down system installed at a dealership as opposed to the assembly plant, the PCM must be enabled. To enable the PCM for extended idle shutdown, refer to the Extended Idle Shutdown Initialization General Procedure in Electronic Engine Controls - Diesel Engine .