Steering Mounted Controls Communication Module: Description and Operation
The microprocessor-based Steering Control Module (SCM) utilizes integrated circuitry to monitor hard wired analog and multiplexed inputs from both
the right and left multi-function switches. In response to those inputs, the internal circuitry of the SCM allow it to transmit electronic message outputs to
the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) over the Local Interface Network (LIN) data bus.
In response to those inputs the internal circuitry and programming of the EMIC, which is also the LIN master module in the vehicle, allow it to control
and integrate many electronic functions and features of the vehicle through both hard wired outputs and the transmission of electronic message outputs to
other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. See: Body and Frame/Body Control Systems/Description and
The SCM is connected to both a fused B(+) circuit and a fused ignition switch output (run-start) circuit. It 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 turning on the lights, prompts the SCM to wake up and transmit on the LIN data
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 SCM or the electronic controls or communication between
modules and other devices that provide some features of the SCM. The most reliable, efficient, and accurate means to diagnose the SCM or the
electronic controls and communication related to SCM operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic