Self-Diagnostic System: Operation: Notes

Signals from major components, sensors and switches to BCM combine with program instructions within system memory, providing accurate control over all subsystems involved. When a subsystem circuit exceeds preprogrammed limits, a system malfunction is indicated and certain back-up functions may be provided. The BCM controls subsystems through direct outputs or through data transmitted along serial data line to one of the other major components. The data communication also gives BCM control over the ECM's self-diagnostic capabilities. Between the BCM and other major components of the computer system, a data line communication process allows devices to share information, providing additional control capability.

In order to access and control BCM self-diagnostic features, 2 electronic components are used, the IPC and the ECCP (or optional CRT monitor). See Figure and Figure .

The service mode for diagnostic information incorporates a 20-character Driver Information Center (DIC) display. The DIC display is located on instrument panel cluster. When a malfunction is sensed by BCM computer system, one of the driver warning messages is illuminated on the DIC. When "service mode" is entered, data parameters, fault codes, inputs, outputs and other features such as override commands, snapshot and code clearing capabilities can be accessed and displayed through CRT or ECCP.

Certain system malfunctions cause computer controlled diagnostic messages and/or telltales to appear, indicating service is required. When a subsystem circuit exceeds preprogrammed limits, a system malfunction is indicated and BCM provides certain back-up functions known as "failsoft". A typical "failsoft" action would be the substitution of a fixed input value when a sensor is detected to be open or shorted. The CRT monitor or ECCP is the controller for entering diagnostics and accessing BCM self-diagnostics. By pressing or touching appropriate buttons on CRT monitor or ECCP, data messages can be sent to BCM, requesting specific diagnostic features. This communication process allows BCM to transfer any of its available diagnostic information to instrument panel 20-character DIC display. When in override mode of BCM diagnostics, information is displayed at ECCP temperature LED display or on CRT monitor.