Speed Control Switch - Operation

OPERATION

The speed control switch pod is a resistor multiplexed unit that provides hard wired inputs to the Powertrain Control Module (PCM) microprocessor. 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 and the horn switch over the LIN data bus to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), which is the LIN master node.

The speed control switch pod for vehicles equipped with the electronic speed control 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 EMIC 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 PCM continually monitors all of the hard wired speed control switch circuits, while the EMIC continually monitors the LIN bus data. The PCM will set a Diagnostic Trouble Code (DTC) for any problem it detects in the speed control switch circuits, and the EMIC will store a Signal Not Available (SNA) code for any LIN bus input errors. The PCM and EMIC also communicate with other electronic modules over the Controller Area Network (CAN) data bus. Therefore, any PCM or EMIC 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 PCM or EMIC 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 PCM, the EMIC 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 PCM, the EMIC 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.