Self-Diagnostic System: Notes

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

A communication process has been incorporated between the BCM (if equipped) and PCM, allowing these units to communicate with each other and share information. The BCM, upon receiving information from the PCM or one of its own related subsystems, compares the received information with programmed instructions within system memory. This allows BCM to monitor individual subsystems and their related sensors and switches.

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

As a result of interactions between the BCM and a malfunctioning component, an alpha-numeric code, known as a trouble code, is often set in the BCM's memory. This trouble code identifies the malfunctioning component and can be accessed by a service technician. On DeVille and Fleetwood, all trouble codes are displayed on the Fuel Data Center (FDC). See Figure . On Eldorado and Seville, all trouble codes are displayed on IPC. See Figure .

In addition to monitoring the self-diagnostic system and displaying trouble codes, the BCM can be programmed by the service technician to perform specific diagnostic tests on individual components and systems.