This vehicle is equipped with a Body Control Module (BCM). The BCM performs multiple body and engine control functions. Several vehicle systems are directly connected to the BCM, such as the audible warnings, interior lighting, door locks, keyless entry, and the Passlock theft deterrent.

This vehicle also has other systems, such as the Powertrain Control Module (PCM), the Electronic Brake Traction Control Module (EBTCM), and the Instrument Panel Cluster (IPC). These vehicle systems communicate with each other on an interconnecting bus, known as the Class II serial data link.

Some electrical components are directly connected and controlled by their system module. Other systems accomplish this by sharing data information with other systems on the Class II serial data link 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 Class II serial data link 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). Thus, when a message is sent out on the Class II serial data link, only the particular system module that was assigned that recognition code will respond to the message.

By communicating data information with other systems on the Class II serial data link, the BCM provides 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, avoid misdiagnosis, and prevent unnecessary parts replacement.