Steering Column Module - Operation

OPERATION

The Steering Column Control Module (SCCM) includes an electronic circuit board, sometimes referred to as the Steering Control Module (SCM). The SCM is a Local Interface Network (LIN) bus master and a gateway for the Controller Area Network (CAN) data bus. Communication - Description.

The microprocessor-based SCM provides power and ground to the multi-function and power tilt and telescope steering column switches of the SCCM, then utilizes integrated circuitry to monitor hard wired analog and digital return inputs from both of these switches. Except for the circuits for the optional heated steering wheel and the standard equipment Driver AirBag (DAB), which are pass-through circuits of the SCCM, the SCM also provides power and ground to all of the electronics carried on the steering wheel through a microprocessor contained in the right steering wheel switch, which is also a LIN slave.

The steering wheel-mounted electronics monitored by the SCM include the horn switch, the speed control switches, the remote radio switches, the hands-free communication switches and the Electronic Vehicle Information Center (EVIC) control switches, if the vehicle is so equipped. The LIN slave monitors the changing states of these switches through both hard wired analog and digital return inputs, then communicates those switch states to the SCM over the LIN bus. In response to those inputs, the internal circuitry of the SCM gateway then transmits electronic message outputs communicating all of the monitored switch state changes as well as SAS data to other electronic modules in the vehicle over the CAN bus.

A fixed connector receptacle of the SCCM connects the SCM to the vehicle electrical system through a single take out with connector from the instrument panel wire harness. The instrument panel wire harness take out has been intentionally provided with additional length to facilitate service removal and installation of the SCCM. However, following SCCM installation, this additional length must be pulled back and secured to the instrument panel structure to prevent the potential for undesirable rattling or buzzing noises while driving.

The SCM is connected to a fused B(+) circuit and receives a path to ground at all times. These connections allow it to remain functional regardless of the ignition switch position. Any input to the SCM that controls a vehicle system function that does not require that the ignition switch be in the ON position such as depressing the horn switch, prompts the SCM to wake up and transmit on the CAN data bus.

The service replacement SCCM is shipped with the clockspring pre-centered within the SCCM and with a plastic locking tab installed. This locking tab should not be removed until the SCCM has been properly installed on the steering column. If the locking tab is removed before the steering wheel is installed on a steering column, clockspring centering must be confirmed by viewing the inspection window on the clockspring rotor. If the black boxes of the clockspring tape are not visible in the inspection window, the entire SCCM must be replaced with a new unit. Service and Repair. Proper clockspring installation may also be confirmed by viewing the Steering Angle Sensor (SAS) data using a diagnostic scan tool.

The hard wired circuits between components related to the SCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.

However, conventional diagnostic methods will not prove conclusive in the diagnosis of the SCCM, the SCM or the electronic controls or communication between modules and other devices that provide some features of the SCCM. The most reliable, efficient, and accurate means to diagnose the SCCM, the SCM or the electronic controls and communication related to SCCM or SCM operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.