Airbag Dm Fault Code 14; Airbag Dm Fault Code 21 - Aston Martin DB7 Workshop Manual

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Electrics
Airbag System
Airbag DM Fault Code 14
Primary crash sensor circuit short to ground
Airbag DM Fault Code 21
Safing sensor insecure mounting.
Normal Operation
The diagnostic module measuresthevoltage at pins
1 -2 and 1 -6. The normal voltage at these pins is 10
volts (±1 volt) with the ignition on, and battery
voltage with the ignition off.
If the voltage at the airbag diagnostic module
connector pins 1 -2 or 1 -6 drops below 5 volts, fault
code 14 will be generated and the airbag warning
lamp will be switched on. When generating a code
14 the diagnostic module also generates a signal to
blow its own internal thermal fuse. This action
disables the airbag deployment circuit. The airbag
diagnostic module fuse is non-repairable and the
module must be replaced after removing the short
circuit. If the voltage at pins 1-2 and 1-6 returns to
normal, fault code 51 (blown thermal fuse) will be
logged.
Fault Analysis
WARNING: Read and adhere to all warnings and
safety procedures at the start of this section when
working on the airbag system.
1. Disarm the airbag system and fit airbag simulators
(6.4.21.4)
2. Disconnect the airbag diagnostic module and
remove the plastic wedge from plug 1 (slate).
Note: The plastic wedge contains a shorting bar which
would short together pins 1-3 (gnd), 1-11 and 1-2 when
the plug is disconnected.
3 Measure the continuity to ground at the following
pins on the diagnostic module harness connector:
1-2 RH crash sensor monitor
1-11 LH crash sensor feed
1 -6 LH crash sensor monitor
1-12 RH crash sensor feed
If no short circuit is detected, go to step 4.
If a short circuit is detected, disconnect the relevant
crash sensorandrepeatthecontinuity measurement
to isolate the circuit fault. Service the wiring or
replace the crash sensor as necessary. Refit the
plastic wedge to the diagnostic module connector.
Fit a new airbag diagnostic module and rearm the
airbags (6.4.21.4).
Normal Operation
The diagnostic module measures the resistance
between pins 1 -10 (safing sensor case ground) and
1-3 (monitor reference ground) at the diagnostic
module connector. If the resistance is greater than
2Q a fault code 21 will be generated and the airbag
warning lamp will be switched on.
Note: a good ground connection is vital. The wire from
pin 1-1 is riveted to the safing sensor case and the case
must be securely grounded to the vehicle body.
Fault Analysis
WARNING: Read and adhere to all warnings and
safety procedures at the start of this section when
working on the airbag system.
Disarm the airbag system and fit airbag simulators
(6.4.21.4).
Disconnect the diagnostic connector and check for
continuity from pin 1-3 to chassis ground.
If continuity is good, go to step 3.
If the resistance reading is 2Q or more, service the
diagnostic module ground circuit to pin 1-3 as
necessary. Confirm a good ground path between
pins 1-10 and 1-3.Clearthecode21 and rearm the
airbags (6.4.21.4).
Check for continuity between pins 1 -10 and chassis
ground at the safing sensor.
If the resistance is above 2Q, check for continuity
from the safing sensor connector pin 5 to chassis
ground. Also check the safing sensor mounting for
corrosion, dirt or loose fixings. Service the wiring
and/or clean and secure the sensor mounting as
necessary, if a satisfactory ground is not achieved,
replace the safing sensor.
Make a final continuity test from diagnostic module
connector pin 1 -3 to 1 -10 to ensure a satisfactory
ground path. Reconnect the diagnostic module.
Clear the code 2 1 . Rearm the airbags (6.4.21.4).
September 1996
6-87