Switch, Speed Control: Operation
The speed control switch pod is a resistor multiplexed unit that provides LIN bussed inputs to the Steering Column Control Module (SCCM) microcontroller integral to the SCCM. The speed control switch pod also contains the circuitry of a Local Interface Network (LIN) slave node, which provides source current for and communicates the switch or sensor states of the Electronic Vehicle Information Center (EVIC) switches, the remote radio switches, the paddle shifter switches (if equipped), the horn switch and the heated steering wheel sensor (if equipped) over the LIN data bus to the SCCM microcontroller, which is the LIN master node.
The speed control switch pod for vehicles equipped with a conventional electronic speed control system and not equipped with the optional Adaptive Cruise Control (also known as the Adaptive Cruise Control/ACC) system contains four switch push buttons whose functions are:
- On/Off - This switch button enables or disables the speed control system and clears any previous speed control set speed from system memory.
- Resume / + - This switch button restores the vehicle to a previously stored set speed or accelerates the vehicle from an already attained set speed.
- Cancel - This switch button cancels the current speed control event, but does not turn the system OFF or clear the currently stored set speed.
- Set / - - This switch button sets the current vehicle speed as the stored set speed or decelerates (coasts) the vehicle to a speed that is slower than the already attained set speed.
The optional adaptive speed control switch pod for vehicles equipped with the ACC system option contains the same four switch push buttons as the conventional speed control switch pod, then adds two buttons whose functions are:
- Mode - This switch button toggles the speed control system between ACC or conventional (non-ACC) modes of operation.
- Distance Buttons - These switch buttons select the separation or following distance (in seconds) that the ACC system maintains between this vehicle and any preceding vehicle.
The SCCM microcontroller LIN master node provides a clean ground and fused B(+) current for all of the switches and sensors on the rotating steering wheel through the LIN slave node circuitry of the speed control switch pod as well as for the Light Emitting Diode (LED) back lighting of both the speed control and the EVIC switch pods. The SCCM microcontroller continually monitors all of the hard wired speed control switch circuits as well as the LIN bus data. The SCCM microcontroller will set a Diagnostic Trouble Code (DTC) for any problem it detects in the speed control switch circuits, and will store a Signal Not Available (SNA) code for any LIN bus input errors. The SCCM microcontroller also communicates with other electronic modules over the Controller Area Network (CAN) data bus. Therefore, any SCCM microcontroller DTC information can be retrieved using a diagnostic scan tool connected to the Data Link Connector (DLC).
The analog resistor multiplexed circuits of the speed control switch pod as well as the hard wired circuits between the switch pod and the SCCM microcontroller 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 LIN slave or master nodes, the SCCM microcontroller or the electronic controls and communication between modules and other devices that provide some features of the speed control system. The most reliable, efficient, and accurate means to diagnose the speed control switch pod, the LIN slave or master nodes, the SCCM microcontroller or the electronic controls and communication related to speed control system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.