Steering Column Lock: Description and Operation

Steering column lock

Steering column lock
The function for the steering column lock is made up by Central electronic module (CEM) and Steering column lock module (SCL). Voltage feed to Steering column lock module (SCL) is controlled by Central electronic module (CEM) via an internal relay in Central electronic module (CEM).
From the Central electronic module (CEM) the Steering column lock module (SCL) also receives commands about when the steering column lock is to be locked or unlocked. The steering column lock is only permitted to perform any function when the vehicle is not moving and the engine is off.
While driving, checks are performed by Central electronic module (CEM) to make sure that the steering column lock is not activated accidentally. At the same time, the Central electronic module (CEM) monitors the communication cable to Steering column lock module (SCL).
If Central electronic module (CEM) detects that Steering column lock module (SCL) begins to communicate when Steering column lock module (SCL) really should have been without voltage, then Central electronic module (CEM) will show a warning message in the display in the Driver information module (DIM) and try to turn off the steering column lock.
Unlocking
When Central electronic module (CEM) receives a signal from the start button, a check is run of key identity, either via the keyless system or via Ignition antenna unit (IAU).
After key validation is complete with approved result, the Central electronic module (CEM) activates voltage feed to Steering column lock module (SCL). During this time, Central electronic module (CEM) performs checks of signals from Engine control module (ECM) and Brake control module (BCM) that the engine is not running and that the vehicle is not moving.
If Central electronic module (CEM) determines that the conditions for unlocking the steering column lock are fulfilled, then Central electronic module (CEM) issues an unlock command to Steering column lock module (SCL). Then Steering column lock module (SCL) attempts to unlock the steering column lock.
If unlocking is successful, Steering column lock module (SCL) sends two signals back to Central electronic module (CEM). One indicates that Steering column lock module (SCL) has not detected any internal problems and works as intended. The other indicates that the lock bolt has reached its unlocked position.
Central electronic module (CEM) will then store a value internally that unlocking has been successful, and will continue to perform the checks that are done for system for immobilizer.
If the steering column lock does not unlock the first time, the steering column lock module (SCL) will make a further two unlocking attempts. The power supply to the Steering column lock module (SCL) is switched off between each attempt. If these also fail, the steering column lock module (SCL) will transmit a message about the fault to the central electronic module (CEM). The central electronic module (CEM) will then store a diagnostic trouble code (DTC) and the checks for the immobilizer system will be cancelled. It will not then be possible to start the engine.
Locking
After the ignition has been switched off and the driver's door opened, the Central electronic module (CEM) checks the signals on CAN that:
- the engine is switched off, from the Engine control module (ECM)
- the vehicle is stationary, from the Brake control module (BCM).
If the engine is switched off and the vehicle does not move then the central electronic module (CEM) will activate the voltage feed to the steering column lock module (SCL). The central electronic module (CEM) will then send signals via LIN to the steering column lock module (SCL) with information that the engine is switched off and that the vehicle is stationary. The central electronic module (CEM) then waits for a reply from the steering column lock module (SCL) that the signals are approved and then sends a message to the steering column lock module (SCL) that locking should be implemented.
Steering column lock module (SCL) sends a message back to Central electronic module (CEM) about if locking was successful or not. If locking still has failed after 3 attempts, then Central electronic module (CEM) will generate a diagnostic trouble code.