airbag LAND ROVER DISCOVERY 1999 User Guide

STEERING
57-6 DESCRIPTION AND OPERATION
Tilt adjustment
The column tilt adjuster lever mechanism is located on the LH side of the steering column and allows the upper column
tube, nacelle and steering wheel assemblies to be tilted up or down a maximum of 7.5° or 47 mm (NAS vehicles have
a smaller range of movement than the ROW vehicles).
The pawl of the mechanism is attached to the lower column and is allowed to pivot, a toothed quadrant is fixed to the
upper column tube.
When the lever on the LH side of the steering column is raised the mechanism releases the pawl from the toothed
quadrant, this allows the column to be moved. When the lever is released two return springs pull the pawl into
engagement with the toothed quadrant.
Steering column lock (All except NAS)
The steering column lock houses the ignition switch, ignition illumination light ring, key lock barrel and the alarm
passive coil. The steering lock is attached to the upper column with two shear bolts. The bolts are tightened to a
torque which shears off the heads of the bolts preventing easy removal of the steering lock.
The steering lock operates by a bolt, which emerges when the ignition key is turned to position 'O' and the ignition key
removed. The bolt engages in a lock collar located on the upper shaft in the upper column tube. The lock collar is
attached to the upper shaft by a 'wave form' interference ring. If a high torque is applied via the steering wheel with
the lock engaged, the lock collar will slip on the upper shaft. This prevents damage to the steering lock, yet still
prevents the vehicle from being driven.
Steering column lock (NAS only)
The steering column lock houses the ignition switch, ignition illumination light ring, key lock barrel and the alarm
passive coil. The steering lock is attached to the upper column with two shear bolts. The bolts are tightened to a
torque which shears off the heads of the bolts preventing easy removal of the steering lock.
The steering column lock operates by a bolt, which emerges when the ignition key is turned to position 'O' and the
ignition key removed. The bolt engages in a groove machined into the upper shaft in the column tube.
Steering wheel
The steering wheel comprises a cast centre and wire frame onto which the soft polyurethane foam is moulded. The
steering wheel is located on the upper column shaft by a spline and is secured with a nut. A remote radio control switch
(if fitted) is located on the LH side of the steering wheel, a cruise control switch may be located on the RH side. Horn
switches are located on each side of the centre of the steering wheel and protrude through the airbag module cover.
Both switches are connected by wires to the rotary coupler connector.
Intermediate shaft
One end of the intermediate shaft is attached to the steering column lower shaft by a splined universal joint and a bolt,
the universal joint is part of a rubber coupling assembly. The rubber coupling assembly is covered by a heat shield
and connects to the lower section of the intermediate shaft via a decouple joint. The rubber coupling reduces the
shocks felt by the driver through the steering wheel. A second universal joint on the other end of the intermediate shaft
is held in by a bolt. The universal joint is splined and engages with the splined rotor (input) shaft of the steering box.
The decouple joint consists of a metal plate that has open ended slots, the plate is bolted through the slots into the
other half of the decouple joint. The top half of the decouple joint has a slot that accepts the lower section of the
intermediate shaft. The slotted metal plate clamps the lower section of the intermediate shaft to the top section. An
indicator clip is installed between the slotted metal plate and the top half of the decouple joint.
If the intermediate shaft is compressed in an accident, the slotted metal plate in the decouple joint will disengage if
sufficient force is applied to the front end of the shaft. If the forces involved do not disengage the shaft, the red
indicator clip located in the decouple joint will break off if the shaft moves. The intermediate shaft cannot be repaired
and must be replaced as an assembly if accident damage occurs.

STEERING
57-52 REPAIRS
Steering wheel
$% 57.60.01.30
Remove
1.Remove drivers airbag.

+ RESTRAINT SYSTEMS, REPAIRS,
Airbag module - drivers.
2.Disconnect horn multiplug.
3.Centralise steering wheel with road wheels in
straight ahead position.
4.Restrain steering wheel and loosen self locking
nut securing steering wheel to column.
5.Release steering wheel from column.
6.Remove and discard self locking nut.
7.Remove steering wheel.
8.Attach tape across edge of rotary coupler to
retain correct setting. 9.Release 2 clips securing each horn button to
steering wheel.
10.Remove screw securing horn earth lead to
steering wheel.
11.Disconnect radio and cruise control multiplugs.
12.Remove 2 screws securing radio switches to
steering wheel.
13.Remove radio switches from steering wheel.
14.Remove 2 screws securing cruise control
switches to steering wheel.
15.Remove cruise control switches from steering
wheel.
16.Remove horns from steering wheel.
Refit
1.Fit horn switches to steering wheel and secure
with clips.
2.Fit and tighten screw securing horn earth lead
to steering wheel.
3.Fit cruise control switches to steering wheel
and secure with screws.
4.Fit radio switches to steering wheel and secure
with screws.
5.Connect radio and cruise control multiplugs.
6.Remove tape from rotary coupler.
7.Ensure road wheels are in straight ahead
position and indicator cancelling cam are
aligned horizontally.
8.Fit steering wheel to column.
9.Connect horn multiplug.
10.Fit and tighten new self locking nut securing
steering wheel to column to 43 Nm (32 lbf.ft).
11.Fit drivers airbag.

+ RESTRAINT SYSTEMS, REPAIRS,
Airbag module - drivers.

RESTRAINT SYSTEMS
DESCRIPTION AND OPERATION 75-1
RESTRAINT SYSTEMS DESCRIPTION AND OPERAT ION
SRS component layout
RHD shown, LHD similar
1DCU
2SRS warning lamp
3Driver airbag module4Driver seat belt pretensioner
5Passenger airbag module
6Passenger seat belt pretensioner

RESTRAINT SYSTEMS
75-2 DESCRIPTION AND OPERATION
SRS block diagram
1DCU
2SRS warning lamp
3Driver airbag module4Driver seat belt pretensioner
5Passenger airbag module
6Passenger seat belt pretensioner

RESTRAINT SYSTEMS
DESCRIPTION AND OPERATION 75-3
Description - SRS
General
The purpose of the Supplementary Restraint System (SRS) is to reduce the impact of the driver and passenger
against the vehicle's interior in the event of a serious accident.
The SRS system is a stand-alone system. There are no remotely mounted crash sensors. The only external input to
the DCU is power. The system only becomes live when the ignition is switched on.
The SRS consists of the following components:
lDiagnostic and control unit (DCU).
lSRS warning lamp.
lRotary coupler.
lDriver airbag module.
lDriver seat belt pretensioner.
lPassenger airbag module.
lPassenger seat belt pretensioner.
The passenger airbag is optional in some markets. All other components are standard fit in all markets. The SRS
functions the same in all markets.

RESTRAINT SYSTEMS
75-4 DESCRIPTION AND OPERATION
Driver airbag module
The driver airbag module is located in the steering wheel and is controlled by the DCU. A bag within the module
inflates to protect the driver in the event of a collision severe enough to deploy the system.
The driver airbag module connects to the steering column wiring harness via a rotary coupler.
Within the driver airbag module is a squib which, when given the correct current by the DCU, inflates the airbag by
initiating a chemical reaction. In deployment, the airbag inflates within a fraction of a second and then deflates at a
controlled rate as the weight of the driver presses against the bag. Vents in the bag control airbag deflation.
The DCU regularly applies a test current to the driver airbag squib to confirm continuity of the ignition circuitry.
The DCU is capable of detecting a short to ground, a short to battery and an open circuit for the driver airbag module
squib. It will also identify if the configuration of the DCU differs from that actually fitted to the vehicle.
The DCU also stores the following additional information on each fault:
lA count indicating the number of times the fault has occurred.
lA start time and an end time for the fault to indicate duration of the fault.

RESTRAINT SYSTEMS
DESCRIPTION AND OPERATION 75-5
Passenger airbag module
The passenger airbag module is located in the instrument panel above the glove box and is controlled by the DCU.
A bag within the module inflates to protect the passenger in the event of a collision severe enough to deploy the
system.
Within the passenger airbag module is a squib which, when given the correct current by the DCU, inflates the airbag
by initiating a chemical reaction. In deployment, the airbag inflates within a fraction of a second and then deflates at
a controlled rate as the weight of the passenger presses against the bag. Vents in the bag control airbag deflation.
The DCU regularly applies a test current to the passenger airbag squib to confirm continuity of the ignition circuitry.
The DCU is capable of detecting a short to ground, a short to battery and an open circuit for the passenger airbag
module squib. It will also identify if the configuration of the DCU differs from that actually fitted to the vehicle.
The DCU also stores the following additional information on each fault:
lA count indicating the number of times the fault has occurred.
lA start time and an end time for the fault to indicate duration of the fault.

RESTRAINT SYSTEMS
75-6 DESCRIPTION AND OPERATION
Seat belt pretensioners
The seat belt pretensioners are located within the front seat belt anchors and are controlled by the DCU. They are
pyrotechnic devices that, when deployed, tighten the front seat belts. This works in conjunction with the airbag
module(s) to protect front seat occupants in the event of an accident.
The DCU regularly applies a test current to the seat belt pretensioner squibs to confirm continuity of the ignition
circuitry.
The DCU is capable of detecting a short to ground, a short to battery and an open circuit for the squibs. It will also
identify if the configuration of the DCU differs from that actually fitted to the vehicle.
The DCU also stores the following additional information on each fault:
lA count indicating the number of times the fault has occurred.
lA start time and an end time for the fault to indicate duration of the fault.

RESTRAINT SYSTEMS
75-8 DESCRIPTION AND OPERATION
Diagnostic and Control Unit (DCU)
The SRS DCU is an electronic single point crash sensor. It is capable of sensing if a crash has taken place. If all the
relevant parameters are met, then the DCU deploys the airbag(s) and seat belt pretensioners.
The DCU is bolted to the transmission tunnel beneath the centre console in the area of the handbrake.
The DCU performs the following functions:
lInternal self test, system monitoring and fault detection.
lSRS warning lamp operation.
lSystem deployment.
Self test, system monitoring and fault detection
The DCU performs a self-test during start-up and then continually during operation of the system. The following
components are tested:
lThe decelerometer.
lThe electromechanical safing sensor.
lThe microprocessor.
lThe continuity of squib ignition circuits.
lThe SRS warning lamp.
If the DCU detects a fault, it stores the fault code in memory. Diagnose the DCU with TestBook. The DCU cannot
be serviced. It must be replaced if it is faulty.
SRS warning lamp operation
The DCU controls the SRS warning lamp contained in the instrument cluster.
System deployment
The DCU determines when the system deploys based on inputs from both the decelerometer and the
electromechanical safing sensor. Both are located within the DCU. Neither are serviceable.
The electromechanical safing sensor uses a magnet and ball bearing system to provide a mechanical confirmation of
vehicle deceleration. The ball bearing is held in place by the magnet. The strength of the magnet is calibrated such
that the force required for the ball bearing to move away from the magnet will only occur if the vehicle decelerates
suddenly, as in an accident.
The SRS deploys only if both the decelerometer reading and the safing sensor operation occur at the same time.

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:
lSRS warning lamp.
lDrivers airbag module.
lPassenger airbag module (where fitted).
lDriver seat belt pretensioner.
lPassenger seat belt pretensioner.
WARNING: The integrity of the SRS system are critical for safety reasons. Ensure the following precautions
are always adhered to:
lNever install used SRS components from another vehicle or attempt to repair an SRS component.
lWhen repairing an SRS system only use genuine new parts.
lNever apply electrical power to an SRS component unless instructed to do so as part of an approved test
procedure.
lSpecial Torx bolts are necessary for installing the airbag module - do not use other bolts. Ensure bolts
are tightened to the correct torque.
lAlways use new fixings when replacing an SRS component.
lEnsure 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:
lThe ignition switch is on.
lThe vehicle decelerates beyond a threshold defined within the DCU.
lThe 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:
lDCU.
lDriver and passenger airbag modules.
lDriver and passenger buckle pretensioners.
lRotary coupler.
lFlyleads (where applicable) connecting airbags and pre-tensioners to SRS harness
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.