Steering Column: Description and Operation
Steering Wheel and Column Description and Operation
The steering wheel and column has 4 primary functions:
* Vehicle steering
* Vehicle security
* Driver convenience
* Driver safety
Vehicle Steering
The steering wheel is the first link between the driver and the vehicle. The steering wheel is fastened to a steering shaft within the column. At the lower end of the column, the intermediate shaft connects the column to the steering gear.
The steering column can be adjusted vertically and longitudinally.
Vehicle Security
Theft deterrent components are mounted and designed into the steering column. The following components allow the column to be locked in order to minimize theft:
* The ignition switch
* The steering column lock
* The ignition cylinder
* The theft deterrent immobilizer module, if equipped
Steering Column Lock
The Steering Column Lock Module (SCLM) controls the steering wheel theft deterrent lock function, which allows the column to be electronically locked. When a valid key is used to start the vehicle, the BCM recognizes this and will send the encrypted password to the SCLM. The SCLM will compare its own stored password to the encrypted password sent by the BCM. If the data matches, the steering column will be unlocked.
In order for the steering column to be locked the SCLM has to see 3 inputs.
1. The BCM power mode is OFF.
2. The vehicle is stationary based on zero speed reported from all ABS wheel speed sensors.
3. The driver or passenger door is opened reported by the PEPS module.
When the SCLM receives these inputs, the steering column will be locked.
The SCLM monitors the column lock system and will set DTC codes when the module detects malfunctions within the system. When a malfunction occurs the driver information center (DIC) will display the Service Column Lock Now message indicating DTC codes are set within the SCLM.
Driver Convenience
The steering wheel and column may also have driver controls attached for convenience and comfort. The following controls may be mounted on the steering wheel or column.
* The turn signal switch
* The headlamp dimmer switch
* The wiper/washer switch
* The horn pad
* The redundant radio/entertainment system controls
* The tilt functions
* The telephone system controls
* The driver information center controls
* The cruise control functions
* The automatic transmission manual setting function
Driver Safety
The steering wheel and column has safety features to protect the driver. The following components may be mounted on or near the steering column:
Energy Absorbing Steering Column
The energy absorbing steering column compresses in the event of a front-end collision, which reduces the chance of injury to the driver. The energy absorbing feature, collapsible steering shaft, and break away mounting features help reduce the injury in the event of an accident.
SIR Coil and Module
For additional information on the operation of the SIR coil and module, refer to SIR System Description and Operation Description and Operation.
Electronic Park Lock/Ignition Lock Cylinder Control Actuator
If the vehicle is equipped with automatic transmission and a floor mounted console gear shift, it has an ignition lock cylinder control actuator system in the steering column. The ignition lock cylinder control actuator purpose is to prevent the ignition key from being turned to the OFF position when the transmission is in any position other than PARK and the vehicle may still be moving. The column ignition lock system consists of an ignition lock cylinder control actuator, and a park position switch that is located in the automatic transmission shift lock control switch. The ignition lock cylinder control actuator contains a pin that is spring loaded to mechanically prevent the ignition key cylinder from being turned to the lock position when the vehicle transmission is not in the PARK position. If vehicle power is lost, and/or the transmission is not in the PARK position the operator will not be able to turn the ignition key to the lock position and will not be able to remove the ignition key from the column. Depending on the implementation, logic might be inverted: Key can be removed by power off.
Steering Wheel Angle Sensor
The steering wheel angle sensor is located somewhere along the steering shaft assembly. The sensor measures the position of the steering wheel and the speed at which it is rotated. A signal representing this measurement is provided to the vehicle stability enhancement system in the ABS module and to the variable effort steering system.
The Theft Deterrent Immobilizer Module
The immobilizer module is mounted in the steering column lock on cars without Passive Entry Passive Start system. Refer to Content Theft Deterrent (CTD) Description and Operation Content Theft Deterrent (CTD).