Airbag Dm Fault Code 33 - Aston Martin DB7 Workshop Manual

Electrics
Airbag System
^^2?
Airbag DM Fault Code 33
Passengers airbag circuit high resistance or open
circuit.
Normal Operation
The diagnostic module measures the resistance
across pins 2-2 and 2-3 every time the ignition is
switched on. The resistance should be 0.9 to 1.1Q.
If the total resistance in the passengers airbag
circuit exceeds 4.0Q, fault code 33 will be declared
and the airbag lamp will be illuminated.
Note: The nominal resistance of the airbag simulator is
2.5£2, therefore expect a total circuitresistancereadingof
2.4 - 2.6Q with the simulator fitted.
Caution: The passenger airbag connector contains
shorting bars which short circuit pins 1 and 3 of
both sides of the connector when disconnected.
DO NOT REMOVE THE AIRBAG SHORTING BAR
UNDER ANY CIRCUMSTANCES.
The harness shorting bar may be temporarily
removed during the following resistance checks.
Possible Causes
• Open circuit or high resistance in the wiring
harness
• Open circuit or high resistance in the passenger
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.
Fault Analysis
1. Disarm the airbag system and fit airbag simulators
(6.4.21.4).
2. Disconnectthediagnostic module and remove the
plastic wedge from connector 2 (black). Measure
the resistance between pins 2-2 and 2-3. The
resistance should be 2.4 - 2.6Q.
if the resistance is 2.4 - 2.6Q, go to step 3.
Ifthe resistance is not in the range 2.4-2.6S2, isolate
the continuity problem noting the following:
a) In the diagnostic module connector, pin 2-2 is
shorted to pin 2-3 by a shorting link when plug
2 of the diagnostic connector is removed.
Removal of the plastic wedge from the plug w i 1 1
remove this short circuit.
b) At the airbag module harness connector, pin 1
is shorted to pin 3 w h e n the airbag is
disconnected. Removal of the plastic wedge
from the plug will remove this short circuit.
c) The shorting link fitted in the airbag module
connector will short pin 1 to pin 3 when the
airbag is disconnected. Do not attempt to
remove this shorting link or the plastic wedge.
Do not attempt to measure the resistance of the
airbag module.
c) Carefully replace all plastic wedges o n
completion of the circuit checks.
3. The fault is therefore in either the airbag module or
in the airbag diagnostic module.
Substitute a known good diagnostic module. If
code 33 recurs with the airbag simulator fitted,
there is still a fault in the wiring or the simulator.
Ifthe fault code 33 does not recur, rearm the airbags
(6.4.21.4) and retest.
If fault code 33 recurs with the airbag module fitted,
the airbag module is faulty. Replace the passengers
airbag module (7.8.02.6).
6-92
September 1996