Data Communications; General Description; Body Control System Description And Operation - Suzuki XL7 2007 Service Manual

Data Communications

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/
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 vehicles 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 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.
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.

General Description

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:
• Antilock brake system (ABS)—Refer to "ABS
Description and Operation: ".
• Automatic day-night mirror—Refer to "Automatic Day-
Night Mirror Description and Operation: ".
• Cruise control system—Refer to "Cruise Control
Description and Operation: ".
• Electrical power management (EPM)—Refer to
"Electrical Power Management Description and
Operation: ".
• Exterior lighting—Refer to "Exterior Lighting Systems
Description and Operation: ".
• Horn system —Refer to "Horns System Description
and Operation: ".
• HVAC—Refer to "Air Delivery Description and
Operation: " and "Air Temperature 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 door lock system —Refer to "Power Door
Locks Description and Operation: ".
• Rear window defogger system —Refer to "Rear
Window Defogger Description and Operation: ".
• Redundant steering wheel controls —Refer to
"Steering Wheel Controls Description and Operation:
".
• Remote function actuation (RFA) control—Refer to
"Keyless Entry System Description and Operation: ".
• Retained accessory power (RAP)—Refer to "Retained
Accessory Power (RAP) Description and Operation".
• Shift lock control system —Refer to "Automatic
Transmission Shift Lock Control Description and
Operation: ".
• Starting system—Refer to "Starting System
Description and Operation: ".
• Supplemental inflatable restraint (SIR) system —
Refer to "SIR 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: ".
Data Communications: 10B-1