Self-Diagnostic System: Notes

NOTE: Terms Electronic Control Module (ECM) and Powertrain Control Module (PCM) refer to same system and are often used interchangeably.

Body Control Module (BCM) and Powertrain Control Module (PCM) are major components of self-diagnostic system. BCM controls a multitude of vehicle functions through monitored sensors and switch inputs and also provides self-diagnostic capabilities. Likewise, PCM provides control and self-diagnostic capabilities in relation to various engine and emission related components it monitors.

Between BCM and PCM, a communication process has been incorporated which allows these units to share information. BCM, upon receiving information from PCM or one of its own related subsystems, compares received information with programmed instructions within system memory. In this way, BCM provides monitoring of individual subsystems and their related sensors and switches.

Should a subsystem exceed preprogrammed limits, BCM will recognize a malfunction and may act to control malfunctioning subsystem. To control a particular subsystem, BCM rapidly switches an internal circuit between zero and 5 volts, converting programmed control information into a series of pulses which are coded data messages. These messages are transmitted to malfunctioning component, which interprets information and responds accordingly.

As a result of interactions between BCM and a malfunctioning component, an alpha-numeric code, known as a trouble code, is often set in BCM memory. This trouble code identifies malfunctioning component and can be accessed by a service technician as an aid to diagnostic procedures. All trouble codes are displayed on Fuel Data Center (FDC).

In addition to monitoring self-diagnostic system and displaying trouble codes, BCM can be programmed by service technician to perform specific diagnostic tests on individual components and systems. Depressing appropriate buttons on Electronic Climate Control Panel (ECCP) will request BCM to provide specific diagnostic information for display on Fuel Data Center (FDC).