1994 JAGUAR XJ6 wiring

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SECTION CONTENTS
m: For ease of access to the required information, this Section has been divided into four sub-sections with the
page numbers of each prefixed 15.1, 15.2, 15.3 or 15.4. Each subsection has its own contents list, and these
are given on the following pages
Sub-Section 15.1 Supplemental Restraint Systems
Subsection Title SRO Page
15.1 ............. Supplemental Restraint System .................................................... 15.1-1
15.1.1 ............ System Description .............................................................. 15.1- 1
15.1.2 ............ Component Descriptions ......................................................... 15.1- 7
15.1.2.1 .......... Diagnostic Module .............................................................. 7 5.1 - 7
15.1.2.2 .......... Wiring Harness ................................................................. 15.1-1
15.1.2.3 .......... AirBagModules ................................................................ 75.1-7
15.1.3 ............ Air Bag Disarming / Arming Procedure ............................................. 15.1-3
15.1.4
............ Diagnostic Module Fault Codes ................................................... 15.1-4
15.1.2.4 .......... ImpactSensors ................................................................. 15.7-2
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15.1 SUPPLEMENTAL RESTRAINT SYSTEM
15.1.1 System Description
The Supplemental Restraint System (SRS) installation comprises:
0 electronic Diagnostic Module (DM)
0 driver and passenger-side air bag modules (including firing mechanisms)
0 two front impact sensors (left and right)
0 one safing sensor
0 dedicated wiring harness
0 two cable reel cassettes (integral part of the steering column harness)
0 Malfunction Indicator Lamp (MIL) and driver information message
The system is designed to provide protection for both driver and front seat passenger by automatically deploying air
bags in the event of a collision during forward travel. The driver
-side air bag is located in the centre of the steering
wheel assembly and the passenger-side air bag in the fascia panel.
In the event of a collision the impact
/ safing sensors operate, completing the electrical firing circuit and causing the
air bags to inflate within 32 milliseconds. At least two of the three sensors (at least one impact, and the safing sensor)
.must be activated to initiate firing. System operation is dependent upon battery voltage supplied directly, and via the
ignition switch, to the DM and the correct installation and operation of all system components, including the wiring
harness. Faults in system components, installation or wiring will be indicated by the MIL Lamp, located on the instru
- ment panel, which will illuminate 'SRS AIR BAG'. Indication is also given by the driver information message'AIR BAG'
displayed on the LCD panel below the speedometer.
15.1.2.1 Diagnostic Module (Fig. I)
The Diagnostic Module (DM), mounted below the passenger-side air bag module, behind the console fascia panel, is
the electronic microprocessor unit which monitors the whole SRS system. The state of the three system sensors, two
air bag modules and the wiring harness is monitored constantly to detect activation criteria and component faults.
15.1.2 COMPONENT DESCRIPTIONS
The unit also confirms correct supply conditions by compar- ing a direct battery voltage input with an input, via the igni- tion switch, of the same voltage value. Detection of system
faults will be relayed by the DM to the instrument panel and
the air bag MIL Lamp illuminated.
The DM contains a reserve power supply unit, enabling the
air bagsto fire even if supply voltage is lost during an impact
situation. The reserve power charge will be retained for ap
- proximately one minute after the positive supply voltage is
disconnected. An auxiliary internal circuit, known as the
'dwell enhancer', provides a temporary ground to compen
- sate for damaged primary crash sensors. If either primary
crash sensor operates for 5 milliseconds the 'dwell en- hancer' circuit will turn on, completing the firing circuit to
ground for 90 milliseconds. The purpose of this is to allow
air bag deployment even if the operated primary crash sen- sor circuit is defective or opens.
15.1.2.2 Wiring Harness
Fig. 1
A dedicated wiring harness, covered with yellow sheathing, independent of any other vehicle system, is used to electri- cally connect all the component items. To allow movement of the steering mechanism, two cable reel cassettes are
incorporated into the driver-side air bag module circuitry, as a means of compensating for steering wheel rotation is
required to prevent harness damage or disconnection. The two cable reel cassettes form an interface between the
steering column and air bag module and, due to their coiled construction, are able to contract or expand as required.
15.1.2.3 Air Bag Modules
The two air bag modules, driver and passenger side, are
each activated when either front impact sensor (Fig. 2) and
the safing sensor operate simultaneously. Both modules
contain a charge of sodium
azide/copper oxide which, when
ignited by an electrical impulse, generate a volume of ni
- trogen gassufficientto inflatetheair bag. Theamountof gas
generated is greater in the passenger-side air bag due to its
larger size. Both modules, including surrounding trim pan- els, are non-serviceable and once activated must be re-
newed as a complete assembly.
Fig. 2
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NO AIR BAG MIl LAMP
Inoperative lamp Circuit or No Ignition to the Diagnostic Module
Normal Operation
The air bag MIL Lamp is designed to illuminate for approximately six seconds when the ignition is switched ‘on’; this
time has been allocated to prove the MIL Lamp operation.
The DM requires an ignition supply to Pin
1, to energize the air bag MIL Lamp circuit. If the MIL Lamp is open circuit
or the DM does not receive ignition voltage at Pin 1, the MII Lamp will not illuminate.
Open circuit in the
MII Lamp supply will cause the DM to emit five tones, or ‘beeps’ every 30 minutes while ignition
is on. Repair faulty circuitry before further diagnostics.
Possible Causes
0 Bulb blown or faulty wiring in the air bag MIL Lamp circuit.
0 Loss of ignition voltage at DM pin 1.
Fault Diagnosis
1. Ignition voltage -check
8 Disarm the SRS system.
8 Switch on the ignition.
8 Measure the voltage between pin 1 (+vel and pin 3 (-vel of the connector.
8 Battery voltage present, proceed with step 2.
8 Battery voltage not present; open circuit on R / W wire from RH fuse-box or faulty ground at pin 3.
8 Check fuse 17, RH fuse-box.
8 Check the fuse connectors and wiring.
8 Check the ground at pin 3 of the DM connector.
8 Arm and verify the SRS system.
2. MIL Lamp open circuit
8 Renew the DM.
8 Arm and verify the SRS system.
If the MIL Lamp is not illuminated, check the bulb, instrument pack and associated wiring.
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FAULTCODE 13
Air Bag Shorted to Ground
Normal Operation
The DM monitors voltage level at pins 11 and 12 which varies in accordance with charging voltage. If voltage measured
at these two pins falls below 2V the MIL Lamp will illuminate and fault code 13 will be present, indicating a possible
short to ground.
During the presence of fault code 13 the DM internal thermal fuse will blow, disabling the air bag deployment circuit.
If voltage to pins 11 and 12 is restored after the fuse has blown, fault code 51, open internal fuse,
will also be present.
Fault code 13 will be present only as long as the short to ground remains.
Possible Causes
Short to ground in any of the following circuits:
0 Air bag supply wiring.
0 Air bag internal.
0 Cable reel cassette internal.
0 Safing sensor supply wiring.
0 Safing sensor internal.
Fault Diagnosis
1. Air bag(s) -short circuit
. Disarm the SRS system.
. Disconnect both air bag modules multi-plug connector.
. Switch ignition ON.
. Is fault code 13 still present ?
Yes - Proceed to step 2.
No - Proceed to step 3.
2. Cable reel cassette
-short circuit
Examine wiring and connector where cable reel cassette mates to the main harness, below the steering column.
If a fault cannot be located, disconnect cable reel cassette from main harness.
. Connect air bag simulator to the main vehicle harness in place of the cable reel cassettes.
. Measure resistance between pin 11 DM and pin 3 (ground).
. Is pin 11 short circuit to ground ?
No - Proceed to fault code 51.
Yes
- Examine wiring and connections between DM, both air bags and safing sensor. Rectify faults as necessary.
If a fault is located, rectify and proceed to step 3.
3. Air bag modules
-check
. Ensure shorting bar is correctly installed to passenger-side air bag connector.
. Measure resistance between connector terminals and module casing.
If resistance value shows a short to ground, renew the module.
. If resistance shows open circuit, repeat test for driver-side module, renew as necessary.
Proceed to fault code 51 on successful diagnosis.
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FAULTCODE 14
Front Impact Sensor Circuit Shorted to Ground
Normal Operation
The DM monitors voltage level at pins 2 and 6. If this voltage falls to 5 volts, or less, the MIL Lamp will illuminate and
fault code 14 will be present, indicating a short circuit to ground on either of the two front impact sensorcircuits. During
the presence of fault code 14 the DM internal thermal fuse will blow, disabling the air bag deployment circuit. If voltage
to pins
2 and 6 is restored after the fuse has blown,fault code 51, open internal fuse will be present. Fault code 14 will
be present only as long as the short to ground remains.
Possible Causes
Short to ground in any of the following circuits:
0 Front impact sensor wiring.
0 Disconnection, or poor connection of harness.
0 Front impact sensors internal ground.
Fault Diagnosis
1. Sub-circuit identification
. Disarm SRS system.
. Remove plastic locking wedge from the grey DM connector.
. Measure resistance between connector pin 3 and all of the following pins; 2,6, 17 and 18.
9 Does any resistance reading indicate short circuit ?
Yes - Renew faulty sensor.
No - Examine sensor wiring harness, locate and rectify faults as necessary.
Proceed to fault code 51 on successful diagnosis.
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FAULTCODE 21
Safing impact Sensor Incorrectly Mounted to Vehicle
Normal Operation
The DM monitors the resistance value between pins 16 and 3. If a resistance value of greater than 2.051 is detected the
MIL Lamp will illuminate and fault code 21 will be present, indicating incorrect mounting of the safing impact sensor.
Secure connections to ground at both the sensor case and the vehicle are necessary to avoid this fault.
Possible Causes
0 Poor or dirty connection between safing sensor case and vehicle ground.
0 Poor or dirty termination at safing sensor internal ground.
0 Open circuit on wiring between DM pin 16 and safing sensor ground terminal.
Fault Diagnosis
1. Resistance - check
Disarm SRS system.
Disconnect battery ground lead.
Measure resistance between pin 3 (ground) and pin 16 (ground - safing sensor).
Is resistance value greater than 251 ?
No - Proceed to step 2
Yes
- Renew DM
2. Sensor ground
-check
Disconnect safing sensor from harness.
Measure resistance between sensor pin 5 and sensor mounting (chassis ground).
Is resistance value greater than 251 ?
Yes - Proceed to step 3
No - Examine wiring between internal sensor ground and harness connection 10. Rectify faults as necessary.
3. Sensor mounting -check
Remove safing sensor from mounting.
* Clean all mounting surfaces thoroughly and refit sensor.
Re-test resistance between harness connection 10 and sensor internal ground.
* Is resistance value greater than 251 ?
Yes - Renew sensor
No - Refit sensor and connect harness and battery ground lead.
4. On completion
Arm and verify the SRS system.
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Vbatt 1 9.0 9.5
10.0 10.5
11.0 11.5 12.0 12.5 ~ 13.0
13.5
Vpin
I 2.3 2.4 2.5 2.7 2.8 3.0 3.1
3.2 1 3.4 3.5
FAULT CODE 22
Safing Impact Sensor
Output Circuit Shorted to Battery Voltage
Normal Operation
The DM measures voltage level at pins 11 and 12 which varies in accordance with charging voltage. If voltage
measured at these two pins exceeds
5V the MIL Lamp will illuminate and fault code 22 will be present, indicating a short
to battery voltage.
14.0 14.5 15.0 15.5 16.0
3.7 3.8 4.0
4.1 4.3
Possible Causes
0 Air bag supply
wiring faulty.
0 Safing impact sensor supply wiring faulty.
0 Safing impact sensor internal contacts short circuit.
0 Cable reel cassette faulty
0 Charging system voltage too high (above 17V).
2. Resistance - check
. Measure resistance across safing sensor contacts.
. Does resistance value indicate open circuit.
Yes
-Examine harness wiring for short circuits. Rectify faults as necessary.
No - Renew safing sensor.
3. On completion
Arm and verify the SRS system.
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FAULT CODE 23
Safing Impact Sensor Input Feed / Return Open Circuit
Normal Operation
The DM monitors the voltage on pins 15 and 23. Thevoltage on both pins should be identical. If a discrepancy between
the two measurements is detected the MIL Lamp will illuminate and fault code 23 will be present, indicating open circuit
between DM and safing sensor.
Possible Causes
Open circuit in wiring between DM pins 15 / 23 and safing sensor or internal sensor connection fault.
Fault Diagnosis
1. Voltage - check
. Disarm the SRS system.
. Measure and compare voltage at both pin 15 and pin 23, using pin 3 as a common ground.
No - Proceed to step 2
Yes - Renew DM
Turn
ignition switch to 'run' and wait 30 seconds.
Is the voltage on both pins between 23V and 26V ?
2. Resistance -check
. Disconnect safing sensor from main harness and measure resistance between YP and RN connector wires.
Is resistance value less than 2S2 ?
Yes - Examine harness wiring for open circuit. Rectify faults as necessary
No - Renew safing sensor
3. On completion
. Arm and verify the SRS system.
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