For 1990-2009 cars

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 GMLAN High speed serial data buss and the GMLAN Low speed serial data buss 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/powertrain control module (ECM/PCM) and vehicle theft deterrent (VTD) control module to communicate without the BCM providing the gateway function.

### Power Mode Master

This vehicle 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, and so the PMM will 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.

### 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 GMLAN high speed buss and the GMLAN low speed buss 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/powertrain control module (ECM/PCM) which is high speed serial data and vehicle theft deterrent (VTD) control module which is low speed serial data. If these modules can not exchange information, the vehicle will not start.

All communication between the BCM and a scan tool is on the High speed GMLAN serial data circuits. A lost communication DTC typically is set in modules other than the module with a communication failure.

### Body Control

The various body control module (BCM) input and output circuits are described in the corresponding functional areas indicated on the BCM electrical schematics. The BCM related systems include, but are not limited to the following:

• | Chimes--Refer to Audible Warnings Description and Operation .

• | Exterior lighting--Refer to Exterior Lighting Systems Description and Operation .

• | Instrument cluster indicator control--Refer to Instrument Cluster Description and Operation .

• | Interior lighting--Refer to Interior Lighting Systems Description and Operation .

• | Power Windows--Refer to Power Windows Description and Operation .

• | Remote function control--Refer to Keyless Entry System Description and Operation .

• | Remote Start--Refer to Keyless Entry System Description and Operation .

• | Retained accessory power (RAP)--Refer to Retained Accessory Power (RAP) Description and Operation .

• | Seat belt use sensing--Refer to Seat Belt System Description and Operation .

• | Theft deterrent--Refer to Immobilizer Description and Operation and Content Theft Deterrent (CTD) Description and Operation .

• | Wiper/Washer System functions--Refer to Wiper/Washer System Description and Operation .