Discovery (1995+): Body Repair Manual — part 8
SUPPLEMENTARY RESTRAINT SYSTEM
1
DESCRIPTION AND OPERATION
SYSTEM COMPONENTS
1. Airbag crash sensors (distributed SRS)
2. SRS warning light (airbag)
3. Rotary coupler
4. Driver’s airbag module
5. Passenger’s airbag module
6. Airbag diagnostic socket
7. Airbag diagnostic control unit
8. Airbag harness (distributed SRS)
9. Knee bolsters (where fitted)
10. Airbag harness
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SUPPLEMENTARY RESTRAINT SYSTEM
2
DESCRIPTION AND OPERATION
OPERATION
The airbag supplementary restraint system (SRS) is a
safety device which, when used in conjunction with
the seat belt, is designed to protect the driver and
front passenger.
Two different SRS systems are fitted to Discovery.
The Distributed SRS which has two crash sensors
located in the engine compartment on the chassis
longitudinals and the Single Point Sensing (SPS) SRS
which has a single crash sensor located in the Airbag
diagnostic control unit.
The change from distributed SRS to SPS SRS
occurred at VINs 198222 and 528977.
Distributed SRS
In the event of a frontal impact, when the airbag
diagnostic control unit and one of the airbag crash
sensors senses the impact, the diagnostic control unit
fires igniters. This in turn ignites tablets of sodium
azide which generate a large amount of Nitrogen gas
leading to airbag inflation in approximately 30
milli-seconds.
SPS SRS
In the event of a frontal impact, when the airbag
diagnostic control unit senses the impact, the
diagnostic control unit fires igniters. This in turn ignites
tablets of sodium azide which generate a large
amount of Nitrogen gas leading to airbag inflation in
approximately 30 milli-seconds.
All Models
When fully deployed the airbag offers additional
protection to the front seat occupant. As an occupant
moves into the airbag it immediately discharges the
gas to provide progressive occupant deceleration and
reduce risk of injuries. The whole process is
completed in approximately 0.3 seconds.
WARNING: All the airbag system
components, including the wiring harness,
MUST be renewed after the airbags have
deployed.
SUPPLEMENTARY RESTRAINT SYSTEM
3
DESCRIPTION AND OPERATION
SRS warning light (airbag)
Distributed SRS
The warning light in the instrument pack illuminates
after the electrical circuits are switched on whilst a
system check is carried out. After about 8 seconds the
warning light will go out. The system checks airbag
diagnostic control unit, airbag crash sensors, airbag
harness, driver and passenger modules.
SPS SRS
The warning light in the instrument pack illuminates
after the electrical circuits are switched on whilst a
system check is carried out. After about 5 seconds the
warning light will go out. The system checks airbag
diagnostic control unit, airbag harness, driver and
passenger modules.
All Models
In the event of a fault in the system the warning light
will illuminate. The airbag diagnostic control unit logs
the fault which can only be accessed using TestBook.
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SUPPLEMENTARY RESTRAINT SYSTEM
4
DESCRIPTION AND OPERATION
GENERAL PRECAUTIONS
Impacts which do not deploy airbags
CAUTION: Check for structural damage in
the area of the impact, paying particular
attention to bumper armatures,
longitudinals, crash cans and bracketry.
1. Carefully inspect any airbag part before
installing. Do not install any part that shows
signs of being dropped or improperly handled,
such as dents, cracks or deformation.
2. Always remove the key from the starter switch
before beginning work.
3. Always disconnect both the negative ’-’ cable
and positive ’+’ cable at the battery before
removal of driver or passenger airbag modules.
Disconnect the negative cable first.
CAUTION: The airbag system has
sufficient stored energy to deploy airbags
for up to 20 minutes.
4. To continue work immediately, disconnect the
driver’s airbag and passenger’s airbag (where
fitted).
5. Do not try to dismantle the airbag module. There
are NO separately serviceable parts. Once an
airbag has been deployed, it cannot be repaired
or reused.
6. Do not install used airbag parts from another
vehicle. When repairing, use only new airbag
parts.
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