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Body Computer Module

Aboard this vehicle are several electronic components which can be controlled by self-diagnostic service technicians to provide valuable self-diagnostic information. These components are part of an electrical network, designed to control various engine and body subsystems.

However, this article will provide a description of the overall electronic network and the on-car diagnostic capabilities which have been designed to aid the service technician in system repair. At the heart of the computer system is the Body Computer Module (BCM). The BCM is located in the middle of the instrument panel, behind the Combo Panel. It has an internal microprocessor which is the center for communication with all the other components in the system. All system sensors and switches are monitored by the BCM or one of the other major components that complete the computer system. These components are:

A combination of inputs from these major components and the other sensors and switches communicate with the BCM, either as individual inputs, or on one of the two common communications links, called data lines. The various inputs to the BCM combine with program instructions within the system memory to provide accurate control over the many subsystems involved.

When a subsystem circuit exceeds preprogrammed limits, a system malfunction is indicated and may provide certain backup functions. Providing control over the many subsystems from the BCM is done by controlling system outputs. This can be either direct or transmitted along the data lines to one of the other components. The process of receiving, storing, testing, and controlling information is continuous. The data communication gives the BCM control over the other component's self-diagnostic capabilities in addition to its own.

Between the BCM and the other major components of the computer system, a communication process has been incorporated, which allows the devices to share information and thereby provide for additional control capability. In a method similar to that used by a telegraph system, the BCM's internal circuitry rapidly switches a circuit between 0 and 5 volts like a telegraph key. This process is used to convert information into a series of pulses which represents coded data messages understood by the other component. Also, much like a telegraph system, each major component has its own recognition code (address). So when a message is sent out on the data line, only the component or station that matches the assigned recognition code will pay attention, and the rest of the components or stations will ignore it.

Below is a list of each individual subsystem that is controlled by the computer system.

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