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 the systems 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.

DTCs Current and History

The BCM stores DTCs as current or history codes. If the BCM detects a system malfunction, the BCM will only store a DTC that corresponds to that particular malfunction. The BCM will not send a message to the IPC to display a message. If a current DTC is stored and the malfunction is no longer present, some DTCs will remain current until the first ignition cycle. Other DTCs will go history when the malfunction is no longer present and does not requires an ignition cycle. History DTCs are intermittent malfunctions and must be diagnosed differently than current DTCs. Refer to Intermittents and Poor Connections .