Steering Column Lock

The central electronic module (CEM) and steering column lock module (SCL) are part of the steering wheel lock function. The power supply to the steering column lock module (SCL) is controlled by the central electronic module (CEM). The steering column lock module (SCL) also receives commands from the central electronic module (CEM) to lock or unlock the steering wheel lock. The function of the steering wheel lock is limited when the vehicle is stationary and the engine is off.

While the vehicle is being driven, the central electronic module (CEM) monitors the communication cable to the steering column lock module (SCL). If the central electronic module (CEM) detects that the steering column lock module (SCL) starts communicating when it should not be powered, the central electronic module (CEM) will display an warning message in the driver information module (DIM) and will attempt to disengage the steering column lock.

Unlocking 

If the keyless vehicle module (KVM) (cars with the keyless entry system only) and central electronic module (CEM) receive a signal from the key-in switch, the identity of the key is checked. This is done either via the keyless system or via the ignition switch. At the same time, the central electronic module (CEM) activates the power supply to the steering column lock module (SCL). After approved validation of the key, the central electronic module (CEM) checks that the engine is not running via CAN signals from the engine control module (ECM). The central electronic module (CEM) also checks that the vehicle is not moving via the CAN signals from the brake control module (BCM) or transmission control module (TCM). If the conditions are met, the central electronic module (CEM) transmits an unlock command to the steering column lock module (SCL). The steering column lock module (SCL) then attempts to unlock the steering wheel lock. If everything is OK, the steering column lock module (SCL) transmits two signals back to the central electronic module (CEM). One signal indicates that the steering column lock module (SCL) has not detected any internal faults and is functioning as intended. The other signal indicates that the spring bolt has moved to the unlocked position. The central electronic module (CEM) will then store an internal value for successful unlocking and then continues with the checks for the immobilizer system.

If the steering wheel lock does not unlock the first time, the steering column lock module (SCL) will make a further two unlocking attempts. 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 

The following applies to vehicles without the keyless entry system 

While the vehicle is in use, the central electronic module (CEM) checks the input signals from the contact breakers for the start control module (SCU) which indicate the position of the ignition key. When the central electronic module (CEM) detects via these contact breakers that the ignition key has been turned to the 0 position and removed from the ignition, the central electronic module (CEM) initiates a locking sequence.

The following applies to vehicles with the keyless entry system 

While the vehicle is in use, the central electronic module (CEM) checks the input signals from the contact breakers for the start control module (SCU) which indicate the position of the starter button. When the central electronic module (CEM) detects, via these contact breakers, that the starter button has been turned to the 0 position and the key-in switch has been deactivated, the central electronic module (CEM) is ready to initiate a locking sequence. During passive starting, the steering column lock is not engaged before the driver's door is opened for safety reasons.

The central electronic module (CEM) then checks that the engine is not running via the CAN signals from the engine control module (ECM). The central electronic module (CEM) also checks that the vehicle is not moving via the CAN signals from the brake control module (BCM) or transmission control module (TCM). If the conditions are met, the central electronic module (CEM) powers the steering column lock module (SCL) and then transmits a lock command to it. The steering column lock module (SCL) sends signals back indicating whether locking was successful or not. The central electronic module (CEM) will store a diagnostic trouble code (DTC) if locking has failed after 3 attempts.