The body control system consists of the body control module (BCM), communications, and various input and outputs. Some inputs, outputs and messages require other modules to interact with the BCM. The BCM also has discrete input and output terminals to
control the vehicle's body functions. The BCM is wired to the high speed GMLAN serial data bus and the low speed GMLAN serial data bus and acts as a gateway between them. If the BCM does not communicate the vehicle will not start due to the inability of the
engine control module (ECM)/powertrain control module (PCM) and theft deterrent module (TDM) to communicate without the BCM providing the gateway function.
Power Mode Master
This vehicles body control module (BCM) functions as the power mode master (PMM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination the power mode that will be sent over the serial data
circuits to the other modules that need this information. The PMM will also activate relays and other direct outputs of the PMM as needed. Refer to
Power Mode Description and Operation for a complete description of power mode functions.
Serial Data Gateway
The body control module (BCM) in this vehicle functions as a gateway or translator. The purpose of the gateway is to translate serial data messages between the high speed GMLAN serial data bus and the low speed GMLAN serial data bus for communication between
the various modules. The gateway will interact with each network according to that network's transmission protocol.
One example of this necessary communication is the communication between the engine control module (ECM)/powertrain control module (PCM) which is high speed serial data and Theft Deterrent Module which is low speed serial data. If these modules
can not exchange information, the vehicle will not start.
A lost communication DTC typically is set in modules other than the module with a communication failure.
Body Control Module
The various body control module (BCM) input and output circuits are described in the corresponding functional areas indicated on the BCM electrical schematics. Some BCM functions with the subsystems may be as a gateway only or as an enable for the system.
The BCM related systems/subsystems include, but are not limited to the following: