Ascender 2WD L6-4.2L (2003)
Body Control System Description And Operation
Body Control System Description and Operation
Fail-safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the BCM fail to send a power mode
message. The fail-safe plan covers modules with discrete ignition signal inputs as well as those modules using exclusively serial data control of power
mode.
Serial Data Messages
The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid BCM message until they can
check for the engine run flag status on the serial data circuits. If the BCM fails, the modules monitor the serial data circuit for the engine run flag serial
data. If the engine run flag serial data is True, indicating that the engine is running, the modules fail-safe to "Run". In this state the modules and their
subsystems can support all operator requirements. If the engine run flag serial data is False, indicating that the engine is not running, the modules
fail-safe to "OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to
both local inputs and serial data inputs from other modules on the vehicle.
Discrete Ignition Signals
Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid BCM message received on the serial data
circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, B+, the
modules will fail-safe to the "RUN" power mode. If the discrete ignition input is not active, open or 0 voltage, the modules will fail-safe to
"OFF-AWAKE". In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local
inputs and serial data inputs from other modules on the vehicle.
