Principles and Operation

This vehicle has five modules that can communicate with a diagnostic tester using the data link connector (DLC). They are the:
^ Powertrain Control Module (PCM)
^ Central Security Module (CSM)
^ Anti-Lock Brake System (ABS) module
^ Air Bag Module
^ Instrument Cluster

The DLC is an interface between various modules on the vehicle and a diagnostic tester. Any module that is capable of communicating with a diagnostic tester is accessed through the DLC. The diagnostic tester can use two possible communication links when accessing the various modules, they are SCP and ISO. The SCP data bus is a two wire, twisted pair communication link, while the ISO data bus, uses one wire to communicate with modules. If one of the two wires in the SCP twisted pair are either open, shorted to ground, or shorted to power a diagnostic connector can still communicate with the module, however, the diagnostic tester will show an error for the circuit that is damaged. The ISO wire has to have integrity to communicate with tester, any damage to the wire will cause the diagnostic data link to be inoperative.

On this vehicle the PCM communicates with the diagnostic tester using the SCP data bus. The air bag module, the ABS module, the CSM and the instrument cluster communicate with the diagnostic tester using the ISO data bus.

Vehicles that are equipped with traction control have an ABS module which is connected to both the SCP and the ISO link. The connection to the SCP link is only used for communication between PCM and ABS module, not for diagnosis.