Expedition 4WD V8-281 4.6L SOHC (1998)
Air Bag Control Module: Description and Operation
WARNING: UNDER NO CIRCUMSTANCES SUBSTITUTE ANOTHER FUSE VALUE FOR THE 10 A BATTERY FUSE. ANY FUSE
OTHER THAN 10 A CAN CAUSE DISARMING FAILURE AND CAN RESULT IN DANGER TO THE OCCUPANTS OF THE VEHICLE.
DO NOT ATTEMPT TO REPLACE THE 10 A BATTERY FUSE UNTIL THE AIR BAG SYSTEM FIRST HAS BEEN DEACTIVATED.
REFER TO DEACTIVATION PROCEDURE. See: Air Bag Systems/Air Bag(s) Arming and Disarming/Service and Repair/Arming and Disarming
NOTE: The safing sensor is internal to the air bag diagnostic monitor and is not replaced separately.
The air bag diagnostic monitor continually monitors all air bag Supplemental Restraint System (SRS) components and wiring connections for possible
faults in the system. If the air bag diagnostic monitor detects a fault in the SRS when the ignition switch is in the RUN position, a Lamp Fault Code
(LFC) will be displayed by the air bag indicator, located on the instrument cluster.
The air bag diagnostic monitor does not deploy the air bag in the event of a collision. The LH or RH air bag sensor and the safing sensor determine when
to deploy the air bag.
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.
LFCs 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.
Each LFC (a series of flashes and pauses of the air bag indicator):
^
represents a two-digit number.
^
is always displayed at least twice.
If the air bag diagnostic monitor detects a fault in the SRS, a Diagnostic Trouble Code (DTC) will be written to the air bag diagnostic monitor
non-volatile RAM (NVRAM). This DTC will then cause the air bag diagnostic monitor to flash an LFC on the air bag indicator. DTCs can be retrieved
with the New Generation Star (NGS) Tester. After repair, the DTC can then be cleared from the NVRAM.
If a system fault is present and the air bag indicator is malfunctioning, an audible chime will be heard. The chime is a series of five sets of five tone
bursts. If the chime is heard, the SRS requires repair.
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 10 A battery Fuse 2.
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. 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.
DTCs are prioritized numerically. If two or more 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.
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 the battery or battery cables are damaged in a collision before safing and air bag sensors close. The backup power supply will deplete its stored
energy approximately one minute after the battery ground cable is disconnected.
