Airbag D M Fault Code 51 - Aston Martin DB7 Workshop Manual

Electrics
Airbag System
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Airbag D M Fault Code 51
Airbag diagnostic module - thermal fuse blown.
WARNING: The diagnostic module will blow the
internal fuse whenever a short circuit to ground
occurs in the deployment circuits. Itdoesnotblow
because of excessive current flow. The thermal
fuse is not a serviceable item. No attempt should
be made to replace or bypass the fuse.
WARNING: Do not install a new diagnostic
module until the short has been located and
corrected. A short which goes away before
corrective action has been taken must be regarded
asan intermittentfault. Installinga newdiagnostic
module when there is an intermittent fault will
result in repeated diagnostic module failures and
repeated repairs.
Fault Analysis
Disarm the airbag system and fit airbag simulators
(6.4.21.4).
Inspecttheconnectorsandterminalsfor any foreign
metal objects or damaged terminals which could
be the cause of the short circuit.
Check each of the circuits in the possible causes list
and isolate the intermittent short circuit. Rectify the
fault.
See the warnings above about replacement of
diagnostic modules when intermittent shorts are
present.
Replace the diagnostic module.
Reconnect all components and rearm the airbags
(6.4.21.4).
Normal Operation
In order to prevent airbag deployment in the event
of a short circuit to ground, the diagnostic module
blows its internal fuse as soon as a short to ground
is detected. This action removes all battery and
back-up power from the deployment circuits. The
diagnostic module w i l l flag the higher priority
codes 13 or 14 while the short to ground exists. If
the short is intermittent and temporarily corrects
itself, the d iagnostic modu le w i 1 1 flag code 51. If the
short to ground returns, the diagnostic module will
again flag the higher priority code 13 or 14 instead
of code 5 1 .
Code 51 after Airbag Deployment
The internal wiring may be shorted to the metal
airbag housings after the airbags are deployed. The
diagnostic module will see this as a short to ground
in the deployment wiring, it will flagacode 14and
blow the internal fuse. As the deployed airbags
cool, the short circuit may rectify itself. The
diagnostic module w i l l then flag a code 5 1 . This
intermittentfault must be investigated and corrected.
Possible Causes
A short circuit to ground in any of the following:
D M pins 2-2, 2-5 or 2-6 to the safing sensor
D M pins 2-2, 2-5 or 2-3 to the passenger airbag
D M pins 2-2, 2-4 or 2-5 to the drivers airbag
D M pins 1 -2 or 1 -11 to RH crash sensor
D M pins 1 -6 or 1 -12 to LH crash sensor
6-98
September 1996