Shaft Lock Module: Operation

The electronic circuitry within the shaft lock module contains all of the logic circuits and components to monitor and control the operation of the shaft locking bolt. The module uses a serial data bus for bi-directional communication with the Sentry Key REmote Entry Module (SKREEM). If the module detects a problem with the positioning or operation of the locking bolt, it sends an error message to the SKREEM. The SKREEM then stores a Diagnostic Trouble Code (DTC) and sends an electronic error message to the ElectroMechanical Instrument Cluster (EMIC) over the Controller Area Network (CAN) data bus, and a SERVICE COLUMN LOCK  textual message will appear in the instrument cluster dot matrix display.

The shaft lock module continuously monitors inputs from the SKREEM and energizes the electric motor to move the locking bolt to the locked or unlocked position based upon that input. If the SKREEM indicates that the key present in the ignition lock cylinder is invalid, the locking bolt remains in the locked position. When the SKREEM indicates that a valid key is present in the ignition lock cylinder, the shaft lock module operates a motor to move the locking bolt to the unlocked position. However, to prevent inadvertent column locking due to a failure while the vehicle is being operated, the module cannot move the locking bolt from the unlocked position to the locked position as long as a key remains in the ignition lock cylinder.

The shaft lock module receives ground at all times through a hard wired remote ground point. The module receives battery voltage to operate and to move the locking bolt in the unlocked direction on a fused B(+) circuit through a fuse in the Junction Block (JB), and receives battery voltage to operate the locking bolt in the locked direction only when the key is removed from the ignition switch. These connections allow the module to remain operational, regardless of the ignition switch position.

For added system security, the shaft lock module learns a unique Secret Key code from the SKREEM over the serial data bus upon initialization. This code is stored in the memory of the module and cannot be changed. Therefore, if the SKREEM requires service replacement, a new shaft lock module will also be required. Another security code, called a PIN, is used to gain access to the SKREEM Secured Access Mode. The Secured Access Mode is required during service to initialize a new shaft lock module.

The hard wired inputs to the module may be diagnosed and tested using conventional diagnostic tools and procedures. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the module electronics, the SKREEM or the serial data bus electronic message communication between these modules. The most reliable, efficient, and accurate means to diagnose the shaft lock module, the SKREEM and the electronic message communication between these modules requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.