Advanced Automotive Fault Diagnosis

Warning
Do not carry out any electrical tests on the air
bag circuit.
9.18.2 Air bags and belt
tensioners fault diagnosis table
Symptom
Possible cause
Warning light on
Wiring fault
Fuse blown on removed
ECU fault
Crash sensor fault
Igniter fault
9.18.3 Deactivation and
activation procedures
Warning
Do not work on air bag circuits unless fully
trained.
Air bag simulators are required to carry out diag-
nosis and testing of the air bag system. For the
frontal air bag(s) this tool is a 2.5 ⍀ resistor, used
to simulate an air bag module connection to the
system. Do not short-circuit the air bag module
connections with a jumper wire. If a jumper wire
is used to short-circuit the air bag module con-
nections, a lamp fault code will be displayed and
a diagnostic trouble code logged by the air bag
control module.
Ford recommend the following procedure for
the air bag system fitted to the Ford Focus.
Deactivation procedure
Warning
The backup power supply must be depleted,
before any work is carried out on the 
supplementary restraint system. Wait at least
one minute after disconnecting the battery
ground cable. Failure to follow this instruction
could cause accidental air bag deployment and
may cause personal injury.
1. Disconnect the battery ground cable.
2. Wait one minute for the backup power supply
in the Air Bag Control Module to deplete its
stored energy.
Warning
Place the air bag module on a ground wired
bench, with the trim cover facing up to avoid
accidental deployment. Failure to follow this
instruction may result in personal injury.
3. Remove the driver air bag module from the
vehicle.
4. Connect the air bag simulator to the sub-
harness in place of the driver air bag module
at the top of the steering column.
5. Remove the passenger air bag module.
6. Connect the air bag simulator to the harness
in place of the passenger air bag module.
7. Disconnect the driver five-way under seat
connector.
8. Connect the air bag simulator to driver five-
way under seat floor harness in place of the
seat belt pretensioner and side air bag.
9. Disconnect the passenger five-way under
seat connector.
10. Connect the air bag simulator to the passen-
ger five-way under seat floor harness in place
of the seat belt pretensioner and side air bag.
11. Reconnect the battery ground cable.

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