airbag disable ASTON MARTIN DB7 1997 Workshop Manual

^7
Electrics
Component Index Sheet 1-97 MY
Component
Name
ABS ECU
ABS Wheel Speed Sensor - Front RH
ABS Wheel Speed Sensor - Front LH
ABS Wheel Speed Sensor - Rear RH
ABS Wheel Speed Sensor - Rear LH
Airbag Crash Sensor RH
Airbag Crash Sensor LH
Airbag Diagnostic Monitor
Airbag (Drivers)
Airbag (Passengers)
Airbag Safing Sensor LHD
Air Conditioning Compressor Clutch
Air Conditioning Control
Air Conditioning Trinary Switch
Air Conditioning Unit
Air Pump
Air Temperature Sensor (IAT1)
Air Temperature Sensor (IAT2)
Alarm LED Inverter
Alarm Sounder
Alternator (Generator)
Ambient Temperature Sensor
Barometric Pressure Sensor
Blower Fan LH
Blower Fan RH
Bonnet Switch
Boot Lamp LH
Boot Lamp RH
Boot Lock Actuator
Brake Fluid Level Sensor
Camshaft Sensor (CMP)
Capacitor (Generator)
Catalyst Overtemperature/Speed Warning Module
CD Autochanger
Central Locking Unit '
Cigar Lighter
Column Switchgear Assembly
Coolant Low Level Sensor
Coolant Temperature Sensor (ECT)
Coolant Temperature Sensor - Temp Gauge
Courtesy Light
Crankshaft Position Sensor (CKP)
Cruise Control Clutch Switch (RHD)
Cruise Control Disable and Stop Lamp Switch
Cruise Control On/Off Switch
Cruise Control Servo Unit
Cruise Control Set Switch
Diagnostic Socket - Lower
Diagnostic Socket - Upper
Door Closed Microswitch (Drivers)
Door Closed Microswitch (Passengers)
Door Lock Motor (Drivers)
Door Lock Motor (Passengers)
Door Lock Switch (Drivers)
Component
Location
(Figure No.-ltem No.)
1-5
1-3
1-3
8-1
8-1
2-3
2-3
4-2
9-6
9-1
2-6
9-4
9-2
9-5
9-2
9-3
3-7
3-11
7-8
2-4
3-12
1-1
8-6
10-10
10-4
2-2
10-8
10-6
10-7
16-3
3-2
1-2
4-8
5-5
6-10
6-5
10-5
10-3
3-4
3-3
10-9
3-1
10-2
1-4
6-6
2-8
6-7
11-3
11-3
7-6
7-6
11-6
11-9
11-5
Circuit
Reference
(Sheet No.-Coordinates)
20-A1
20-D2
20-D3
20-B6
20-C6
3-D1
1-C3
11-C6
9-A3
11-C4
12-B4
3-C1
3-D3
3-D1
11-CI
1-C2
5-C1
5-B3
14-B6
1-B2
5-A6
1-A2
4-A4
8-A3
12-C3
1-C5
15-A4
16-D3
16-C6
20-B3
5-C1
5-A5
11-C3 Japan Only
10-B3 Rear of Radio
12-D4
13-A3
9-A2
3-A3
5-B1
5-C1
9-B1
5-A2
3-C5
9-A3
13-A5
2-A6
13-B5
10-A6
10-A5
21-A2
22-A2
21-B1
22-Bl
21-A2
September 1996 6-43

Electrics
Airbag System ^2?
Airbag DM Fault Code 13
Airbag circuit short to ground
Normal Operation
The diagnostic modu
le
measures the voltage at pins
2-5 and 2-6. The voltage at these pins is dependant
on charging system voltage as shown in the table

belovi-.

'in 2-5
2.3V
2.4 V
2.5V
2.7V
2.8V
3.0V
3.1V
3.2V
3.4V
3.5V
3.7V
3.8V
4.0V
4.1V
4.3V
Pin 2-6
2.3V
2.4V
2.5V
2.7V
2.8V
3.0V
3.1V
3.2V
3.4V
3.5V
3.7V
3.8V
4.0V
4.1V
4.3V
Charge Volts
9.0V
9.5V
lO.OV
10.5V
11.OV
11.5V
12.0V
12.5V
13.0V
13.5V
14.0V
14.5V
15.0V
15.5V
16.0V
If the diagnostic monitor measures a voltage of 2.0
volts or less on pins 2-5 and 2-6, a fau It code 13 will
be generated and flashed to the instrument pack to
be signalled on the airbag warning lamp. Voltages
as low as 2.0 volts indicate a possible short to
ground in these circuits.
When generating a code 13 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 repairing the short circuit, if the
voltage at pins 2-5 and 2-6 returns to normal, fault
code 51 (blown thermal fuse) will be stored in
memory.
6.
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 airbag diagnostic module. Switch
on the ignition.
Measure the continuity to ground at the following
pins on the diagnostic module harness connector:
2-2 Passenger airbag feed
2-3 Passenger airbag return
2-4 Drivers airbag return
2-5 Drivers airbag feed
2-11 Safing sensor feed
If no short circuit is detected, go to step 4.
If
a
short circuit is detected, disconnect the relevant
airbag simulator or the safing sensor and repeat the
continuity measurement to isolate the circuit fault.
Service the wiring or replace the safing sensor as
necessary. Fit a new airbag diagnostic module and
rearm the airbags (6.4.21.4).
Check for intermittent short circuits in the cable
reel cassette. Monitor the continuity to ground at
pins 2-4 and 2-5 whilst rotating the steering from
lock to lock in both directions.
If no short circuit is detected, go to step 5.
If a short circuit is detected, replace the column
switchgear assembly. Fit a new airbag diagnostic
module and rearm the airbags (6.4.21.4).
WARNING: Do not attempt to make any electrical
measurements on the airbag
modules.
Any induced
voltage can
cause
the airbag
to
deploy with the
risk

of personal
injury.

Fit a replacement diagnostic module and
replacement airbag modules.
Caution: Do not refit
the
old
airbag
modules.
They may

be faulty and would
damage the
new diagnostic module.
Rearm the airbag system (6.4.21.4).
6-86 September 1996

mxm^^^?
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
21.
Rearm the airbags (6.4.21.4).
September 1996 6-87

in:m3'^?
Electrics
Airbag System
Airbag DM Fault Code 34
Drivers airbag circuit low resistance or short circuit.
Normal Operation
The diagnostic module measures the resistance
across pins 2-5 and 2-4 every time the ignition is
switched on. The resistance should be 1.6 to 1.8Q.
This value is made up of the airbag
1
.OQ and the
cable reel cassette windings 0.3-0.4£2 per winding.
If the total resistance in the passengers airbag
circuit falls below 0.7Q, fault code 34 will be
declared and the airbag lamp will be illuminated.
Note: The nominal
resistance
of the airbag simulator is
2.5Q, therefore expect
a
total circuit resistance readingof
3.1 -
3.3£2
with the simulator
fitted.

Caution: The drivers airbag connector contains
shorting bars which short circuit pins 1 and 3 of
both sides of the connector when disconnected.
DO NOT REMOVE THE AIRBAC CONNECTOR
SHORTING BAR UNDER ANY CIRCUMSTANCES.
The airbag harness shorting bar may be temporarily
disabled during the following resistance checks.
Possible Causes
• Poorly mated cable reel cassette connector. If
the connector is poorly mated, the shorting bars
may not be fully retracted.
• Faulty shorting bar may short circuit 2-4 and 2-
5 together.
• Short circuit in the cable reel cassette windings.
• A short across the airbag terminals in the airbag
module.
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 2-5 and 2-4. The
resistance should be 3.1 - 3.3Q.
If the resistance is 3.1 to 3.3Q, go to step 4.
If the resistance is below 3.1 - 3.3Q, go to step 3.
Disconnect the cable reel cassette connector at the
steering column and remove the plastic wedge.
Measure the resistance from pins 2-4 and 2-5 at the
diagnostic module connector.
If the resistance is infinity, check the cable reel
cassette for short circuits. Replace the column
switchgear assembly if necessary. Refit the plastic
wedges. Reconnect the diagnostic module. Clear
the code 34. Rearm the airbags (6.4.21.4).
If the resistance is less than infinity, replace the
main airbag harness. Refit the plastic wedges.
Reconnect the diagnostic module. Clear the code

34.
Rearm the airbags (6.4.21.4).
Since the circuit resistance is in specification, the
fault must lie in the diagnostic module or in the
airbag module.
Substitute a known good diagnostic module. If
code 34 recurs with the airbag simulator fitted,
there is still a fault in the wiring or the simulator.
If the fault code 34 does not recur, rearm the airbags
(6.4.21.4) and retest.
If fault code 34 recurs with the airbag modulefitted,
the airbag module is faulty. Replace the drivers
airbag module (4.5.01.3).
September 1996 6-93

Electrics
Airbag System ^^?
Airbag DM Fault Code 35
Passengers airbag circuit low resistance or short
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 falls below 0.7S2, fault code 35 will be
declared and the airbag lamp will be illuminated.
f^ote:
The
nominal
resistance
of the airbag simulator
is

2.5£2,
therefore expect
a
total circuit
resistance
reading of
2.4 - 2.6Q with the simulator fitted.
Caution: The passengers airbag connector contains
shorting bars which short circuit pins 1 and 3 of
both sides of the connector when disconnected.
DO NOT REMOVE OR DISABLE THE AIRBAG
CONNECTOR SHORTING BAR UNDER ANY
CIRCUMSTANCES.
The airbag harness shorting bar may be temporarily
disabled during the following resistance checks.
Possible Causes
• Poorly mated airbag harness connector. If the
connector is poorly mated, the shorting bars
may not be fully retracted.
• Faulty shorting bar may short circuit 2-2 and 2-
3 together.
• A short across the airbag terminals in the
passengers airbag module.
Fault Analysis

1.
Disarm the airbag system and check the security of
the passengers airbag module connector before
disconnecting.
If the connector is secure, complete the disarming
procedure, fit the airbag simulators (6.4.21.4). Go
to step 2
If the connector is insecure, service as necessary,
clear the code 35, rearm the airbags. Check that
code 35 does not recur.

2.
Disconnectthediagnostic module and removethe
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 4.
If the resistance is below 2.4 - 2.6fl, go to step 3.
3. Disconnect the airbag simulator at the passengers
airbag module and remove the plastic wedge from
the harness connector. Measure the resistance
between pins 2-2 and 2-3 at the diagnostic module
connector.
If the resistance is infinity, the airbag harness is
good at this time. Swap the airbag simulators at the
drivers and passengers airbag connectors. Repeat
the resistance check. If the resistance is less than
infinity, there is a fault in the passengers airbag
harness connector. Service the connector or replace
the harness as necessary. Refit the plastic wedges.
Reconnect the diagnostic module. Clear the code

35.
Rearm the airbags.
If the resistance is less than infinity, service the
bulkhead harness as necessary. Refit the plastic
wedges. Reconnect the diagnostic module. Clear
the code 35. Rearm the airbags (6.4.21.4).

4.
Since the circuit resistance is in specification, the
fault must lie in the diagnostic module or in the
airbag module.
Substitute a known good diagnostic module. If
code 35 recurs with the airbag simulator fitted,
there is still a fault in the wiring or the simulator.
If the fault code 35 does not recur, rearm the airbags
(6.4.21.4) and retest.
If fault code 35 recurs with the airbag module fitted,
the airbag module is faulty. Replace the passengers
airbag module (7.8.02.6).
6-94 September 1996