Section 307 (Speed Control (Service Information)): Operation: Operation

The vehicle operator controls all speed control system features through the speed control switch pod on the face of the right horizontal spoke of the steering wheel. When a push button of the switch pod is depressed, it provides a hard wired resistor multiplexed analog input to the Powertrain Control Module (PCM).

The PCM reads the speed control switch input, along with other hard wired and electronic message inputs received from other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. The PCM software continually monitors these inputs as well as electronic vehicle distance  message inputs from the Antilock Brake Module (ABM) (also known as the Controller Antilock Brake/CAB or the Electronic Stability Control/ESC module) and numerous hard wired inputs including the brake (or stop) lamp switch, then provides the appropriate electronic message and hard wired outputs to invoke the requested and programmed electronic speed control features.

The PCM microcontroller continuously monitors all of the speed control system electrical circuits to determine the system readiness. If the PCM detects a monitored system fault, it sets and stores a Diagnostic Trouble Code (DTC). The PCM uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with the diagnostic scan tool using the CAN data bus. This method of communication is used for control of the Cruise indicator and the Malfunction Indicator Lamp (MIL) (also known as the Check Engine lamp) in the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) and for system diagnosis and testing through the 16-way Data Link Connector (DLC) located on the driver side lower edge of the instrument panel.

The hard wired inputs and outputs for the PCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the PCM or the electronic controls or communication between other modules and devices that provide features of the speed control system. The most reliable, efficient, and accurate means to diagnose the PCM 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.