The Body Control Module (BCM) uses information from other vehicle systems, such as the Powertrain Control Module (PCM), in order to perform some of its functions. Before starting BCM diagnosis, read the circuit information and learn how the BCM operates and interacts with other vehicle system. Understanding how the BCM operates will reduce diagnostic time, avoid misdiagnosis, and prevent unnecessary parts replacement.

Use a scan tool (Tech 2) to diagnose the BCM when specified in the diagnostic tables. A scan tool displays Diagnostic Trouble Codes (DTCs), the status of BCM inputs and outputs, and commands BCM outputs on and off. Refer to Diagnostic Trouble Code (DTC) Displaying for more information.

Become very familiar with the BCM capabilities and diagnostic features. These self-diagnostic features are referenced in the diagnostic tables and are very useful in diagnosing non-DTC setting malfunctions as well.

Replace the BCM only when a diagnostic table specifically direct you to do so. BCM inputs and outputs are protected against shorts to battery or ground. Therefore, do NOT replace the BCM after repairing a short in the wiring. After repairing the wiring, perform the BCM diagnostic system check to verify the repair. Most malfunctions related to a vehicle system, such as the BCM, are traceable to faulty wiring, connectors and terminals, and occasionally some other component. Refer to Diagnostic System Check - Body Control System for more information.

The BCM is a very reliable component and it is not likely the cause of the malfunction. Replacing the BCM before a complete diagnosis will usually result in a recurrence of the original malfunction.

The BCM stores DTCs as current or history DTCs. If the BCM detects a malfunction, the BCM stores a DTC that corresponds to that particular malfunction. The BCM does not send a message to the instrument cluster to display a message, such as turning on a warning indicator lamp. If the BCM stores a current DTC and the malfunction is no longer present, some DTCs will remain current until the next ignition cycle. Other DTCs change from current to history without requiring a new ignition cycle when the fault is no longer present. History DTCs are intermittent malfunctions and must be diagnosed differently than current DTCs. Refer to Intermittents and Poor Connections for more information.