Expedition 2WD V8-281 4.6L VIN W EFI (1997)
Air Bag Control Module: Description and Operation
PURPOSE
Performing system diagnostics is the main purpose of the air bag diagnostic monitor.
The air bag diagnostic monitor continually monitors all air bag system components and wiring connections for possible faults when the ignition switch
is in RUN position.
OPERATION
It does not deploy the air bags in the event of a collision. The air bag diagnostic monitor operates in the following manner:
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If the air bag diagnostic monitor detects a fault in the air bag system, a Diagnostic Trouble Code (DTC) will be written to the air bag
diagnostic monitor's Non-Volatile Random Access Memory (NVRAM).
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This DTC will then be displayed on the air bag indicator lamp.
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After servicing, the DTC may then be cleared from NVRAM.
AIR BAG SYSTEM FUNCTIONS
Other important features of the air bag diagnostic monitor and its functions within the system are described below. It is necessary that these key
features and functions are well understood.
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The air bag diagnostic monitor illuminates the air bag indicator for approximately six seconds when the ignition switch is in the RUN position and
then turns the indicator off. This shows that the air bag indicator is operational. If the air bag indicator does not illuminate or the indicator stays on
or flashes at any time, a fault has been detected by the air bag diagnostic monitor.
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DTCs may not be displayed for approximately 30 seconds after the ignition switch is placed in the RUN position. This is the amount of time the
air bag diagnostic monitor requires to perform all tests and verify system faults, if present.
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Each diagnostic trouble code (a series of flashes and pauses of the air bag indicator) represents a two digit number. Each diagnostic trouble code is
always displayed at least twice. For example, a diagnostic trouble code 32 is displayed as three flashes, followed by a one second pause, then two
flashes, followed by a three second pause.
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If a system fault is present and the air bag indicator is malfunctioning, an audible tone will be heard, indicating that system service is required.
CAUTION: The thermal fuse does not blow (open) because of excessive current flowing through it. Do not attempt to jumper out the thermal
fuse with a circuit breaker or any other type of fuse.
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If a fault exists that makes unwanted air bag deployment possible, the air bag diagnostic monitor will attempt to remove deployment power by
turning on a solid state switch to blow the 10A battery fuse 2.
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If the 10 A battery fuse has successfully been blown by the air bag diagnostic monitor, the air bag diagnostic monitor will not attempt to blow it
again until the proper fault has been repaired and cleared (see Diagnostic Trouble Code Clearing procedures for details). The air bag diagnostic
monitor will store both the unwanted deployment DTC and the loss of deployment power DTC. The loss of deployment power DTC is the highest
priority.
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Diagnostic trouble codes are prioritized numerically so if two or more different faults occur at the same time, the fault having the highest priority
will be displayed first. After that fault has been corrected, the next highest priority fault will be displayed.
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The air bag diagnostic monitor includes an internal backup power supply. This feature provides sufficient backup power to deploy the air bag in
the event that the battery or battery cables are damaged in an accident before the center air bag and front air bag sensors close. The backup power
supply will deplete its stored energy approximately one minute after the positive battery cable is disconnected.
