General Information

This vehicle is equipped with a computer system capable of performing multiple engine and body control functions. Vehicle components (windows, locks, mirrors, etc.) are controlled directly by their system module. Each system communicates with other systems on an interconnecting bus or serial data line. These systems are all part of the vehicle's computer system providing two-way communication between various engine and body control systems.

Some electrical components are directly connected and controlled by their system module. Others systems accomplish this by sharing data information with other systems on the serial data line to execute various vehicle functions. All system data information (sensors, switches, etc.) can be monitored by any system module that completes the computer system.

All systems on the same serial data line use a communication process similar to a telephone system, where enormous amounts of information can be exchanged on a single data wire.

Communications between each system is accomplished by sending a digitally coded message, consisting of specific information a system module must follow. Each system module is assigned its own recognition code (address). So when a message is sent out on the serial data line, only the particular system module that was assigned that recognition code will responded to the message.

The BCM, which is the power mode master, is responsible for sending the power mode messages on the serial data line to other systems. Power mode messages consist of ignition switch position status information, and allows other systems (that are not directly wired to ignition power) away to determine which position the ignition switch is in. When the power mode message is sent, other systems respond to this message by entering a power-up state and sending a State of Health Code (SOH) code message. This SOH message indicates they are able to communicate information between other systems. By communicating data information with other systems on the same serial data line, either input information or specific program information within the systems memory, can provide more accurate and reliable computer system control functions. The BCM uses information from other systems in order to execute some functions. Therefore, before further diagnosis, review the general information on how the BCM computer system operates and how each system interacts with the BCM. This will save diagnostic time, future misdiagnosis, and unnecessary parts replacement.