Principles of Operation: Diagnosis

The FEM, REM and DDM constantly monitor systems under their control and report a concern in the form of a diagnostic trouble code (DTC). DTCs can be retrieved with the diagnostic tool or an equivalent tester through the SCP communication network.

This vehicle's design makes it unique in that electronic functions are divided into zones. The DDM controls features near the driver front door. The FEM controls features in the front portion of the vehicle and the REM controls the features in the rear portion. These systems rely heavily on the SCP communication network in order to transmit and receive messages. It is vital when diagnosing this vehicle's electronic systems, to understand:

• Where the input (command) originates.
• All input information messages necessary in order for a feature to operate correctly.
• Which module(s) receive(s) the input (or command message).
• If the module which received the input (message) controls the output of the feature, or does it output a message over the communication network to another module.
• Which module controls the output of the feature.