Wiring Systems and Power Management
7-435
Wiring Systems and Power Management
Description and Operation
Power Mode Description and
Operation
3282831
Power to many of this vehicles circuits is controlled by
the module that is designated the power mode master.
This vehicles power mode master is the body control
module (BCM). The BCM has multiple B+ circuits that
feed into it. Each of those circuits are partitioned within
the controller to drive certain outputs of the vehicle
’
s
body functions. An open or short in any one of the B+
circuits may induce multiple codes/or a section of
non-functionality within the BCM with the rest of the
BCM functioning normally. In this case it is useful to
refer to the power distribution schematics to determine
if the non-functional partition of the controller shares a
common B+ circuit. The ignition switch is a low current
switch with multiple discrete ignition switch signals to
the power mode master for determination of the power
mode that will be sent over the serial data circuits to the
other modules that need this information. The power
mode master will also activate relays and other direct
outputs of the power mode master as needed. The
power mode master determines which power mode
(Off, Accessory, Run, Crank Request) is required, and
reports this information to other modules via serial data.
Modules which have switched voltage inputs may
operate in a default mode if the power mode serial data
message does not match what the individual module
can see from its own connections.
The power mode master receives ignition switch
signals to identify the operators desired power mode.
The Power Mode Parameter tables below illustrate the
correct state of these input parameters (circuits) in
correspondence to the ignition switch position:
Power Mode Parameters
Ignition Switch
Position
Power Mode
Transmitted
Ign. Off/Run/Crank
(Off/Run Crank
Voltage Circuit)
Ignition
Accessory/Run
(Accessory Voltage
Circuit)
Ignition Run/Crank
(Ignition 1 Voltage
Circuit)
Off Key Out
Off
Key Out / ACC
Inactive
Inactive
Off Key IN
Off
Key In / Off
Inactive
Inactive
2021 - Silverado 4500HD, 5500HD, and 6500HD Electrical Body Builder Manual
