BCM System, Part I: Operation

The BCM communicates with these major components, sensors and switches; either as individual inputs or on the common communication link, the Serial Data Line (SDL). These various inputs to the BCM combine with programmed instructions in the system memory to provide control over the subsystems. When a subsystem circuit exceeds pre-programmed limits, a system malfunction is indicated and may provide certain back-up functions.

Control over the subsystems from the BCM is done by controlling system outputs. This can be direct or transmitted along the serial data line to 1 of the other major components. The process of receiving, storing, testing and controlling information is continuous. The data communication gives the BCM control over the ECM self-diagnostic capabilities, in addition to its own.

A communication process is incorporated between the BCM and the other major components to allow the devices to share information and thereby provide additional control capability. The BCM's internal circuitry rapidly switches a circuit between 0 and 5 volts. This is used to convert information into a series of pulses which represent coded data messages understood by the other components. Each major component has its own recognition code. So when a message is sent out on the serial data line, only the component that matches the assigned recognition code will pay attention. The rest of the components will ignore it.

In order to access and control the BCM self-diagnostic features, Riviera models use a CRTC and CRT. Riviera models use a 22-character display area on the CRT as part of the CRT "Service Mode" to display diagnostic information. When a malfunction is sensed by the computer system, 1 of the driver warning messages is displayed on the CRT under the "DIAGNOSTIC" category. When the "Service Mode" is entered, the various BCM, ECM or IPC faults can be displayed. In addition, Fault Codes, inputs, outputs, override commands and clearing code capability are displayed, when commanded through the CRT.

The CRT is used to enter diagnostics and access the service diagnostics routines. The CRTC controls the CRT display and interprets the switches touched on the CRT and passes this information to the BCM. This communication process allows the BCM to transfer any of its available diagnostic information to the CRT for display during "Service Mode". By touching the appropriate pads on the CRT, data messages can be sent to the BCM from the CRTC, over the serial data line, requesting the specific diagnostic feature required.

In order to access and control the BCM self-diagnostic features, Toronado models use an IPC and ECC. Toronado models use a 20-character display area called the Information Center. During normal engine operation, this area displays "TORONADO" or is a tachometer, displaying engine RPM. When a malfunction is sensed by the BCM, 1 of the driver warning messages is displayed in this area. When the diagnostic mode is entered, the various ECM and BCM codes are displayed. In addition to the ECM and BCM codes, discrete inputs and outputs, and BCM output override messages are also displayed when called up through the ECC.

The ECC panel provides the controls for the heating and A/C systems. It also becomes the controller by which to enter diagnostics and access the BCM self-diagnostics. This communication process allows the BCM to transfer any of its available diagnostic information to the instrument panel for display during service. By pressing the appropriate buttons on the ECC, data messages can be sent to the BCM over the serial data line, requesting the specific diagnostic features desired. When in the override mode of the BCM diagnostics, the amount of override is displayed at the ECC, where the outside and set temperatures are normally displayed.