Discovery 2. Manual — part 642

RESTRAINT SYSTEMS

DESCRIPTION AND OPERATION

75-9

Operation - SRS

The diagnostic and control unit (DCU) controls the SRS system. The DCU is located beneath the centre console close
to the handbrake area. The DCU contains both an electronic deceleration sensor as well as an electromechanical
safing sensor. When the electronic deceleration sensor within the DCU detects rapid deceleration of the vehicle, it
compares the deceleration rate with stored values in its' memory. If the deceleration rate exceeds the stored value
and the electromechanical safing sensor triggers, the DCU deploys the airbag and the seat belt pretensioners. The
DCU will not deploy the airbags and seat belt pretensioners unless both sensors trigger.

The SRS has diagnostic capabilities through TestBook. In the event that a fault is detected, the DCU alerts the driver
by illuminating a warning lamp in the instrument cluster.

The DCU controls the following:

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SRS warning lamp.

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Drivers airbag module.

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Passenger airbag module (where fitted).

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Driver seat belt pretensioner.

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Passenger seat belt pretensioner.

WARNING: The integrity of the SRS system are critical for safety reasons. Ensure the following precautions
are always adhered to:

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Never install used SRS components from another vehicle or attempt to repair an SRS component.

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When repairing an SRS system only use genuine new parts.

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Never apply electrical power to an SRS component unless instructed to do so as part of an approved test
procedure.

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Special Torx bolts are necessary for installing the airbag module - do not use other bolts. Ensure bolts
are tightened to the correct torque.

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Always use new fixings when replacing an SRS component.

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Ensure the SRS Diagnostic Control Unit (DCU) is always installed correctly. There must not be any gap
between the DCU and the bracket to which it is mounted. An incorrectly mounted DCU could cause the
system to malfunction.

System deployment
The airbag and seat belt pretensioners deploy to protect the front seat occupants when the DCU senses a rapid
vehicle deceleration. The system deploys when the following conditions are met:

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The ignition switch is on.

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The vehicle decelerates beyond a threshold defined within the DCU.

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The electromechanical safing sensor within the DCU triggers.

When all of the above conditions are met, the DCU deploys the airbag(s) and seat belt pretensioners. If the above
conditions are not met, the DCU will not deploy the system.

Component replacement policy
After an impact which deploys the airbags and pretensioners, the following components must be renewed:

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DCU.

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Driver and passenger airbag modules.

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Driver and passenger buckle pretensioners.

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Rotary coupler.

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Flyleads (where applicable) connecting airbags and pre-tensioners to SRS harness

RESTRAINT SYSTEMS

75-10

DESCRIPTION AND OPERATION

SRS warning lamp
The SRS warning lamp illuminates for 5 seconds during system readiness check on starting the engine. The SRS
warning lamp extinguishes for one second after the system readiness check is performed. If a fault is present the
warning lamp then illuminates continuously. If no fault is present, the SRS warning lamp remains extinguished. If a
system fault occurs in excess of two seconds after the readiness check has been completed, the SRS warning lamp
illuminates for that ignition cycle. It remains illuminated for a minimum of 12 seconds

±

4 seconds for all fault

conditions.

The SRS warning lamp will only illuminate for low voltage concerns while the low voltage condition is present. If the
low voltage condition is corrected, the SRS warning lamp extinguishes and the fault is recorded in the DCU's memory.

RESTRAINT SYSTEMS

DESCRIPTION AND OPERATION

75-11

DESCRIPTION AND OPERATION

Description - seat belts

An inertia reel, three point seat belt is installed at each seat position. The inertia reels incorporate a liftshaft locking
system with webbing sensor and car sensor activating mechanisms. The webbing sensor activates the locking system
if the webbing is subjected to a sharp pull. The car sensor activates the locking system if the vehicle is subjected to
sudden deceleration or a severe tilt angle.

Front seat belts
The inertia reel of each front seat belt is attached to the related B/C post, behind the finishers. The webbing runs from
the inertia reel, through a height adjuster, to an anchor point at the base of the B/C post. The buckle assembly for
each belt is attached to the inboard side of the seat and contains the SRS pretensioner.

Rear seat belts
The inertia reels for the outboard rear seats are attached to the body behind the loadspace side trim casings. The
webbing runs from each inertia reel through an upper mounting, suspended from the cantrail, to an anchor point on
the rear wheel arch.

The inertia reel of the centre rear seat is mounted in the back of the seat. The webbing runs through a guide on the
top of the seat and is anchored to one of the seat hinge points. The buckles for the rear seat belts are also attached
to the seat hinge points.

Third row seat belts
The inertia reel of each third row rear seat belt is attached to the related E post, behind the loadspace side trim
casing.The webbing runs from the inertia reel, through an upper mounting on the E post to an anchor point on the
loadspace floor. The buckle is mounted on the inboard side of the seat.

RESTRAINT SYSTEMS

75-12

DESCRIPTION AND OPERATION