Airbag Dm Fault Code 32 - Aston Martin DB7 Workshop Manual

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Electrics
Airbag System
Airbag DM Fault Code 32
Drivers airbagcircuit high resistance or open circuit.
Normal Operation
The diagnostic module measures the resistance
across pins 2-4 and 2-5 every time the ignition is
switched on. The resistance should be 1.6 to 1.8£2.
This value is made up of the airbag 1 .OQ and the
cable reel cassette windings 0.3-0.4Q per winding.
If the total resistance in the drivers airbag circuit
exceeds 4 . 0 ^ , fault code 32 will be declared and
the airbag lamp will be illuminated.
Note: The resistance of the airbag simulator is 2.5Q,
therefore expect total resistance readings of 2.8 - 2.9Q
with the simulator fitted.
Caution: The drivers airbag and the cable reel
cassette connectors contains shorting bars which
short circuit pins 1 and 3 of the connectors when
disconnected.
DO NOT REMOVE THE AIRBAG SHORTING BAR
UNDER ANY CIRCUMSTANCES.
The harness shorting bars may be temporarily
removed during the following resistance checks.
Possible Causes
• Excessive resistance in the cable reel cassette
connections.
• Open circuitor high resistance in the cable reel
cassette windings.
• Open circuit or high resistance in the wiring
harness
• Open circuit or high resistance in the drivers
airbag module.
• Defective diagnostic module.
WARNING: Do not attempt a direct resistance
check on the airbag module. Accidental
deployment can occur due to the induced voltage
from the measuring equipment.
3.
Fault Analysis
Disarm the airbag system and fit airbag simulators
(6.4.21.4).
Disconnect the diagnostic module and remove the
plastic wedge from connector 2 (black). Measure
the resistance between pins 2-4 and 2-5. The
resistance should be 2.8 - 2.9Q.
If the resistance is 2.8 - 2.9Q, go to step 3.
if the resistance is not in the range 2.8 - 2.9D, isolate
the continuity problem noting the following:
a) Pin 2-4 is shorted to pin 2-5 by a shorting link
. when plug 2 of the diagnostic connector is
removed. Removal of the plastic wedge from
the plug will remove the short circuit.
b) Both halves of the cable reel conneaor have
shorting links which will short pin 1 to pin 3
when the connection is removed. Removal of
the plastic wedge horn either half will remove
the short circuit in that part of the wiring.
c) A shorting link is fitted in the airbag module
connector. Do not attempt to remove this
shorting link or the plastic wedge. Do not
attempt to measure the resistance of the airbag
module.
d) Carefully replace all plastic wedges on
completion of the circuit checks.
The fault is therefore in either the airbag module or
in the airbag diagnostic module.
Substitute a known good diagnostic module. If
code 32 recurs with the airbag simulator fitted,
there is a fault in the wiring.
If the fau It code 32 does not recur, rearm the airbags
(6.4.21.4) and retest.
If fau It code 32 recu rs with the ai rbag modu le fitted,
the airbag module is faulty. Replace the drivers
airbag module (4.5.01.3).
September 1996
6-91