1997 ASTON MARTIN DB7 wiring

Electrics
Airbag System ^?
Airbag DM 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 will 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 wi
11
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 51.
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 will then flag a code 51. This
intermittentfault must be investigated and corrected.
Possible Causes
A short circuit to ground in any of the following:
DM pins 2-2, 2-5 or 2-6 to the safing sensor
DM pins 2-2, 2-5 or 2-3 to the passenger airbag
DM pins 2-2, 2-4 or 2-5 to the drivers airbag
DM pins
1
-2 or
1 -11
to RH crash sensor
DM pins
1
-6 or
1
-12 to LH crash sensor
6-98 September 1996

in:[M3^?
Electrics
Airbag System
Airbag DM Fault Code 52
Back-up power supply - voltage boost fault.
Normal Operation
A back-up power supply consisting of a capacitor
and voltage booster is contained within the
diagnostic module. The voltage booster charges
the capacitor to 24 ±
1
volt when the ignition is on.
The back-up power supply is connected to
diagnostic module pin 1-9 via a diode. Since the
resistance of pin 1-9 to ground is infinite, the
capacitor has no discharge path and the back-up
supply
is
maintained ata high
voltage.
Thediagnostic
module monitors this voltage and will flag a code
52 if a minimum of 23V is not achieved within 45
seconds of switching on the ignition.
Possible Causes
Low back-up supply voltage may be caused by:
• Partial or total short circuit of pin 1-9 to ground.
• Boost circuit failure within the diagnostic
module.
Fault Analysis

1.
Disarm the airbag system and fit airbag simulators
(6.4.21.4).

2.
Disconnect the diagnostic module. Check for a
partial or permanent short circuit to ground from
diagnostic module harness connector pin 1-9.
If no short circuit is detected, go to step 3.
If a short circuit is detected, service the wiring as
necessary. Reconnectthediagnostic module. Clear
the code 52. Rearm the airbags.
3. Using a high resistance digital multimeter, set up to
measure the voltage from diagnostic module pin
1
-
9 to ground. Switch on the ignition.
If the voltage is in the range 24 ± 1 volt, the back­
up power supply is good. Suspect an intermittent
short circuit to ground and recheck the output
circuit from pin 1-9.
Ifthe voltage is below the range 24 ±
1
volt, replace
the diagnostic module.

4.
Rearm the airbags (6.4.21.4).
Airbag DM Fault Code 53
internal diagnostic module failure.
Normal Operation
The diagnostic module constantly measures the
voltage on pins
1
-2,
1
-6,
1 -11
and
1
-12. It should
be 10
±1
volt. The voltage is regulated by a resistor
within the diagnostic module and the resistance to
ground ofpins
1-2,6,11
and 12 should be infinite.
The resistance across the normally open contacts of
the crash sensors should also be infinite. If the
resistance of the pins to ground or across the crash
sensors becomes measurable, the voltage wi
11
drop.
At between 5V and lOVthe diagnostic module will
recognise an internal voltage regulation failure and
flag a code 53 fault and the airbag warning light will
be illuminated.
Notes: A dead short to ground in the
crash
sensor circuits
will drop the voltage below 5V and the diagnostic
module will flag
a
code
14
fault.

The
diagnostic module
performs several self-tests as
the
ignition is switched on. If it fails any
test,
fault code 53
will be flagged.
Possible Causes
• A decrease in resistance from infinity between
the primary crash sensor circuits and ground.
• An internal diagnostic module self-test failure.
Fault Analysis

1.
Disarm the airbag system and fit airbag simulators
(6.4.21.4).

2.
Check each of pins 1-2, 1-6, 1-11 and 1-12 for
continuity to ground.
If resistance of all circuits is infinity, go to step 3.
If any resistance other than infinity is detected,
service the circuit wiring as necessary. Reconnect
all connectors and switch on and clear all fault
codes.
Switch off the ignition and then switch on again.
Check that the airbag warning lamp comes on at
'ignition on' and extinguishes after approximately
six seconds on satisfactory completion of the airbag
system self-check.
3. Rearm the airbags (6.4.21.4).
September 1996 6-99

D=27
Electrics
Seat Belt Pretensioner
050C Pretensioner Squib High Resistance 050D Pretensioner squib low resistance
050C will be logged if the resistance of the
pretensioner squib circuit rises above 4.5 ±0.5C2
050D will be logged if the resistance of the
pretensioner squib circuit falls below 1.4 ±0.4Q
Procedure
Read the warnings given at the start of this
pretensioner diagnostics section.
Connect the PDU to the lower diagnostic socket
and access the pretensioner control module. Verify
that an 050C code is logged and note if the fault is
shown as internnittent. Note any other codes in the
DTC log and then clear ail codes.
Switch off the ignition and wait at least 10 minutes
for the pretensioner squib firing capacitors to fully
discharge before continuing with this procedure.
Disconnect the pretensioner squib connector at the
rearward harness. Disconnect the pretensioner
control module and temporarily cheat the squib
shorting link.
3.
Procedure
Read the warnings given at the start of this
pretensioner diagnostics section.
Connect the PDU to the lower diagnostic socket
and accessthe pretensioner control module. Verify
that an 050D code is logged and note if the fault is
shown as intermittent. Note any other codes in the
DTC log and then clear all codes.
Switch off the ignition and wait at least 10 minutes
for the pretensioner squib firing capacitors to fully
discharge before continuing with this procedure.
Disconnect the pretensioner squib connector atthe
rearward harness. Disconnect the pretensioner
control module and temporarily cheat the squib
shorting link.
Note: The control module harness connector has a
shorting link which
short
circuits the squib
lines together

when the connector is displaced. Carefully insert a
suitable non-metallic
cheater to
remove
the short
circuit
between pins 11 and 12 before continuing with fault
diagnosis.
.j^ 'o o ob bo oooooooo
O O O
iV ^3 ^3 ^3 ^3 ^3 ^
lU Insert cheater here
Check the continuity of the squib feed and return

lines.
If any significant resistance is measured,
service the wiring as necessary.
Also check the condition of the connector pins for
damage or lack of tension and service
as
necessary.
If the circuit resistance is acceptable and the
connector pins are good, go to step 6.
If any defects are identified and serviced, go to step
7.
If the checks in step 4 are good, the high circuit
resistance must be in the pretensioner squib or in
thecontrol module. Replace the pretensioner squib
and reconnect all components.
Clearall logged DTCs from the pretensioner control
module and then test the vehicle.
If the 050C code is logged again, replace the
control module.
Note: The control module harness connector has a
shorting link which
short
circuits the squib
lines together

when the connector is displaced. Carefully insert a
suitable non-metallic
cheater to remove the
short circuit
between pins 11 and 12 before continuing with fault
diagnosis.
Insert cheater here
Check the continuity from the squib feed line to the
squib return line. With the shorting link cheated,
the resistance should be more than lOkQ. If the
resistance is less than 10kQ, service the wiring as
necessary.
Also check the connector pins for any damage
which could cause an unintentional short circuit.
If the checks in step 5 are good, the low circuit
resistance must be in the pretensioner squib or in
thecontrol module. Replace the pretensioner squib
and reconnect all components.
Clearall logged DTCs from the pretensioner control
module and then test the vehicle.
If the 050D code is logged again, replace the
control module.
September 1996 6-107

Electrics
Seat Belt Pretensioner
Check the continuity of
the
line from pretensioner
control module pin 2 to instrument pack green
connector pin 2.
If continuity is approximately
OQ,
go to step 5.
If the line resistance
is
significantly greater
than
OQ,
service the wiring as necessary. Reconnect all
components and test the vehicle to ensure that the
problem is resolved.
Ifthe lamp
and
wiring
checks are
good,
the
fault lies
in the instrument pack or in the control module.
Replace the control module and retest. Ifthe fault
persists, replace the instrument
pack.
Reconnectall
components and test the vehicle to ensure that the
problem is resolved.
Pretensioner Control Module Internal
Faults
The following codes indicate internal faults within the
pretensioner control module.
0209 Safing sensor error
030A Temperature sensor error
0D13 Capacitor voltage error
0D14 Capacitor capacitance
0D09 Energy reserve switch
0D1E Energy shutdown switch
050E Seatbelt pretensioner switch error
0109 Accelerometer function
01OA Acceleration out of range

01 OB
Acceierometer offset
OAOC Analogue voltage error
090A EEPROM not programmed
0909 EEPROM checksum
090C RAM check error
060E Warning lamp driver error
0A09 Communications error
OAOA External watchdog error
OAOB External watchdog time out
020A Safing sensor not closed
If any of the above codes are logged, replace the
pretensioner control module.
September 1996 6-109

^^2?
The Aston Martin Lagonda Diagnostic System
Users Guide
Airbag System Diagnostics
WARNING: Whilst it
is
completely safe to
access

and read the airbag diagnostic module memory at
the diagnostic socket, significant personal risks
exist in the performance of any other
tasks
on the
airbag system or components. Therefore all
workshop manual warnings must be read and all
safety procedures must be followed before, during
and on completion of any other practical work on
the airbag system.
System Description
The airbag system installation comprises:
Airbag Diagnostic Module
Driver and passenger airbag modules
Two front impact (crash) sensors
One 'safing' sensor
Dedicated wiring harness
SRS indicator/warning lamp
The system is designed to provide protection for both
driver and front seat passenger by automatically
deploying airbags in the event of a collision during
forward travel.
Intheeventof
a
collision, the crash and safing sensors
will operate, completing the firing circuit and causing
the airbags to inflate within 32 milliseconds. At least
one crash sensor and the safing sensor must operate to
fire the airbags.
Any faults in system components, installation or wiring
will be indicated by a flashing code on the SRS/
AIRBAG warning lamp. Fault code information may
also be monitored using the PDU or scan
tool.

A full description of the airbag system components is
included in the workshop manual.
Airbag Diagnostics
The Airbag Control Module indicates a fault by
transmitting a pulsed signal down the Airbag System
Failure line to flash the SRS/AIRBAC warning lamp.
The fault code is repeated continuously. If there are
two or more faults, the fault code with the highest
priority is transmitted first. The second fault code is
only transmitted when the first fault has been rectified.
TheSRS/AIRBAC warning lamp is also used to indicate
any problem in the seat belt pretensioner system (if
fitted). Flashing of the lamp indicates an airbag fault,
constant illumination of the lamp indicates a seat belt
pretensioner fault.
At the top left of the PDU screen there is a bullet mark
which indicates the current state of the Airbag System
Failure line. As a code is transmitted the bullet mark
can be seen to flash.The PDU reads the fault code, and
writes the code number and fault description to the

screen.
The PDU continues to monitor the transmitted

code.
If the transmitted code changes, the new code
number and description will appear below the first.
PMC Airbag
32 Drivers airbag circuit
shorted or open
o
when remedial action has been taken to correct a
fault, press the Clear Button to clear down the PDU
display. Then use the PDU to ensure that no faults are

reported.

A series of audible beeps, continuously transmitted by
the Airbag Diagnostic Module, indicates that there is
an Airbag System fault to report and that the Airbag
System Failure line
is
open circuit. The PDU is notable
to monitor the fault line in this situation as there is no
pull-up resistor, normally provided by a warning lamp
in the instrument pack.
Rapid continuous flashing of the Instrument Pack
Airbag Failure Lamp indicates that both front impact
sensors are disconnected. No fault code is reported on
the PDU, however on close inspection the bullet mark
can be seen to flicker.
September 1996 9-45

^^?
The Aston Martin Lagonda Diagnostic System
Users Guide
Operation
On selection of DMM the general screen, as shown in Fig.

1,
will be displayed.
Voltage is the default selection for measurement, with red
and black probes selected
as
sources.
To choose alternatives
to these options, press the relevant description for change
followed by the 'tick' icon in the top, right-hand, corner.
If the measurement mode (Voltage) is selected for change,
followed by a confirming 'tick', a screen as show will be

displayed.

Select DMM Measurement
^Q^||[
Resistance
Pulse Period
Pulse Width
(low)
Voltage (AC)
Frequency
Pulse Width
(High)
Duty Cycle
DMM Measurement Selection
Selection of any option from this screen, followed by a
confirming 'tick', will return the operator to the general
screen but with the new mode displayed against DMM.
If 'Resistance' is selected an additional
icon,
showing an
audio symbol, will appear above the "EXIT" display. This
icon allows the enabling / disabling of an audible signal
which sounds when measured valuefal
Is
below 0.5 ohms.
Touch the icon to toggle the warning ON / OFF directly,
no confirming 'tick' is necessary. A 'cross' is displayed
over the icon when warning is turned OFF.
Measurement Source Selection
If
a
measurement source (either RED or BLACK PROBE) is

selected,
a screen as shown will be displayed. This screen
may vary depending upon the various probes which can
be connected to the PDU.Afull list of possiblesources will
be displayed on the 'Source Select' screen.
Select (-) Channel
BLACK Probe
Battery positive
Battery negative
Module pin
Selection of (+) and (-) measurement channels
Selection of any source option, except "Module Pin", will
return the user to the general screen, which will display
the revised source.
Module Pin Selection (Air-Con only)
Selection of "Module Pin" will display a screen as shown.
Selection of one of the options displayed on this screen
allows the operator to make measurements on designated
pins of the air conditioning control module. When the air
conditioning module is selected PDU will display a wiring
connection diagram, as shown.
Cable Setup
Module Connection
September 1996 9-51

The Aston Martin Lagonda Diagnostic System
Users Guide [S:S3^2?
The PDU will then check the cable connections. Until all
connections are correct, the PDU will not allow progression
beyond this
screen.
Pressingthe'asterisk'icon and selecting
abort returns the operator to the general screen if an
incorrect system has been chosen.
If selection and wiring are correct a numeric keypad will
be displayed. The operator can nowenterapin numberto
be tested, using this keypad.
Pin
Numeric Keypad
Display Freezing
To assist the operator a "HOLD/UPDATE" option is
displayed on the general screen. This option is selected as
default on the general screen and allows a reading to be

'frozen'
on screen when the 'tick' icon is pressed. A 'tick'
button is also incorporated into the red probe so that a
remote 'freeze' command can be sent to PDU, holding the
reading until the operator can view the screen. A frozen
value is displayed on a 'grey' background indicating that
the value is on HOLD. Re-pressing the 'tick' icon (either
local or remote) unfreezes the display and restores the
normal display background.

b.nn

DMM
(-)
(-)
Voltage
RED PROBE
BLACK PROBE
HOLD/UPDATE
The "HOLD/UPDATE" option operates on one touch of
the 'tick' icon (or 'tick' button) irrespective of the state of
the screen backlight. Therefore it is not necessary to
reinstate the screen backlight if there has been no operator
contact with the PDU for five minutes (or longer). Pressing
"HOLD/UPDATE" reinstates the backlight and initiates/
releases display 'freeze' automatically.
System Exit
At any point during DMM operation it is possible to exit
the system by either pressing the 'asterisk' icon and
selecting abort, or pressing "EXIT" (where available)
followed by a confirming 'tick'.
The Hold/Update option
9-52 September 1996