Yukon Denali AWD V8-6.2L (2007)
Body Control Module: Description and Operation
BODY CONTROL SYSTEM DESCRIPTION AND OPERATION
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 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, 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.
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 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 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.
Communication between the BCM and a scan tool can be on the high speed GMLAN network or low speed GMLAN network. If one network is lost,
the BCM can still communicate with the scan tool. 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:
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Antilock Brake System (ABS)-Refer to ABS Description and Operation (Under 8600 GVW ) ABS Description and Operation (Equal to or Over
8600 GVW).
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Automatic Day-Night Mirror-Refer to Automatic Day-Night Mirror Description and Operation.
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Cruise Control System-Refer to Cruise Control Description and Operation.
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Electrical Power Management (EPM)-Refer to Electrical Power Management Description and Operation.
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Exterior Lighting-Refer to Exterior Lighting Systems Description and Operation.
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Horn System-Refer to Horns System Description and Operation.
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HVAC-Refer to Air Delivery Description and Operation and Air Temperature Description and Operation.
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Instrument Cluster Indicator Control-Refer to Instrument Cluster Description and Operation.
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Interior Lighting-Refer to Interior Lighting Systems Description and Operation.
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Power Door Lock System-Refer to Power Door Locks Description and Operation.
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Rear Window Defogger System-Refer to Rear Window Defogger Description and Operation.
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Redundant Steering Wheel Controls-Refer to Steering Wheel Controls Description and Operation.
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Remote Function Actuation (RFA) Control-Refer to Keyless Entry System Description and Operation.
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Retained Accessory Power (RAP)-Refer to Retained Accessory Power (RAP) Description and Operation.
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Shift Lock Control System-Refer to Automatic Transmission Shift Lock Control Description and Operation.
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Starting System-Refer to Starting System Description and Operation.
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Supplemental Inflatable Restraint (SIR) System-Refer to SIR System Description and Operation.
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Suspension System-Refer to Electronic Suspension Control Description and Operation.
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Theft Deterrent-Refer to Content Theft Deterrent (CTD) Description and Operation.
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Tire Pressure Monitor (TPM) System-Refer to Tire Pressure Monitor Description and Operation.
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Wiper/Washer System Functions-Refer to Wiper/Washer System Description and Operation.
Export Body Control Module
The export body control system has an additional body control module located in the rear of the vehicle. This additional body control module is
referred to as the XBCM. The XBCM has discrete input and output terminals to control additional vehicle body functions not supported by the
primary body control module (BCM). The XBCM is wired to the GMLAN low speed serial data buss and the BCM and acts as a gateway between
them. If the XBCM does not communicate, various rear end lighting such as rear fog lamps and trailer lighting will be impaired.
The various input and output circuits are described in the corresponding functional areas indicated on the XBCM electrical schematics. Some XBCM
functions with the subsystems may be as a gateway only or as an enable for the system. The XBCM related systems/subsystems include, but are not
limited to the following:
