The BCM uses information from other systems in order to execute some functions. Therefore, before further diagnosis, review the general information on how the BCM operates and how each system interacts with the BCM. This will save diagnostic time, future misdiagnosis, and unnecessary parts replacement.

Use a scan tool in order to diagnose the BCM when referred to in diagnostic procedures. In addition to displaying DTCs, the BCM displays the input status and the data values used. The BCM can also command many of its subsystems ON and OFF. Any of these features can be selected using the scan tool.

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

Replace the BCM only if the diagnostic procedures specifically direct you to do so. Every input to the BCM and every output from the BCM is short to ground/short to battery protected. Therefore, the BCM does not automatically need to be replaced when a short is found in the wiring. Repair the wiring first. Then check the system for further problems. Most system malfunctions are traceable to faulty wiring and connectors, and occasionally components. The BCM is very reliable and not the likely cause of a system malfunction. BCM replacement before a complete diagnosis will usually result in a recurrence of the original complaint malfunction.

The BCM has the ability to store DTCs as current or history codes. When the BCM stores a DTC, the BCM may send a massage on the serial data line to the Instrument Panel Cluster (IPC) to display a warning message indicating a DTC is current. For most DTCs, the BCM will NOT display a warning message. Current DTCs can be stored in two classifications: latched, and unlatched. Latched current codes are those indicating a malfunction is present, but will still remain current even after the malfunction no longer exists. These current codes will continue to display as current until the ignition is cycled OFF then ON. Unlatched codes will clear as soon as the malfunction is no longer present and does not require the ignition to be cycled. History DTCs are those indicating that the BCM previously detected a malfunction which later disappeared. The reason could be either that the malfunction is intermittent, only happening occasionally, or that the system for which the DTC is set is not currently being operated. History DTCs are intermittent malfunctions and must be diagnosed differently than current DTCs. Refer to Intermittents and Poor Connections .