Thunderbird V8-281 4.6L SOHC (1994)
Air Bag Diagnostic Module: Description and Operation
PURPOSE
The air bag diagnostic monitor performs system diagnostics, which is its main purpose. It continually monitors all air bag system components and
wiring connections for possible faults in the system.
OPERATION
The air bag diagnostic monitor does NOT deploy the air bags in the event of a crash! The crash sensors are hard wired to the air bags, and therefore
the crash sensors determine when to deploy the air bags. The air bag diagnostic monitor displays a Diagnostic Trouble Code (DTC) by flashing the air
bag warning indicator if it detects a fault in the air bag system when the ignition switch is in RUN.
AIR BAG SYSTEM FUNCTIONS
Several important features of the air bag diagnostic monitor and its functions within the system are described below. It is necessary that you
understand these key features and functions. They will enable you to understand and perform efficient air bag system diagnostics.
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The air bag diagnostic monitor illuminates the air bag warning indicator for approximately six seconds when the ignition switch is turned to RUN
and then turns it off. This indicates that the air bag warning indicator is operational. If the air bag warning indicator does not illuminate or if the air
bag warning indicator stays on or flashes at any time, a fault has been detected by the air bag diagnostic monitor.
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Diagnostic trouble codes may not be displayed for approximately 16 seconds after the ignition switch has been switched to RUN. This is the
amount of time it takes the air bag diagnostic monitor to perform all tests and verify any system faults.
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Diagnostic trouble codes are displayed as a series of flashes and pauses of the air bag warning indicator. Each diagnostic trouble code, or series of
flashes, represents a two- digit number. For example, a Diagnostic Trouble Code 32 is displayed as follows:
flash flash flash - (one-second pause) - flash flash - (three-second pause)...
flash flash flash - (one-second pause) - flash flash - (three-second pause)...
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If a system fault exists and the air bag warning indicator is malfunctioning, an audible tone will be heard indicating the need for service. The tone
is a series of five sets of five beeps. This DOES NOT indicate a diagnostic trouble code 55. It means that the air bag warning indicator is out and a
system fault exists that requires service.
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If a fault exists that makes unwanted air bag deployment possible, the air bag diagnostic monitor has an internal thermal fuse that will blow
automatically. This removes all power to the air bag deployment circuit. The air bag warning indicator will flash the appropriate code to indicate
the suspect circuit.
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The thermal fuse is controlled by the air bag diagnostic monitor and is not serviceable.
NOTE: The thermal fuse does not blow because of excessive current flowing through it. DO NOT attempt to short circuit the thermal fuse with a
circuit breaker of any other type of fuse.
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Diagnostic trouble codes are prioritized numerically so that if two or more different faults occur at the same time, the fault having the highest
priority will be displayed first. The highest priority fault will be displayed until it is corrected. After it has been corrected, the next highest priority
fault will be displayed.
WARNING: The back-up power supply energy must be depleted before any air bag component service is performed. To deplete back-up
power supply energy, disconnect the positive battery cable and wait one minute to avoid accidental deployment and possible personal injury.
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The air bag diagnostic monitor includes an internal back-up power supply. This feature provides sufficient back-up power to deploy the air bags in
the event that the battery or battery cables are damaged in a collision before the crash sensors close. The back-up power supply will deplete its
stored energy approximately one minute after the positive battery cable is disconnected.
NOTE: When the battery has been disconnected or reconnected, some abnormal drive symptoms may occur while the Powertrain Control Module
(PCM) relearns its adaptive strategy. The vehicle may need to be driven 16 km (10 miles) or more to relearn the strategy.
WARNING: To avoid personal injury the air bag simulator(s) must be removed and the air bag(s) reconnected before the system is
reactivated.
