sensor LAND ROVER DISCOVERY 2002 Workshop Manual

REAR SUSPENSION
DESCRIPTION AND OPERATION 64-11
1Battery supply (via SLABS relay)
2Ignition supply
3RH height sensor
4LH height sensor
5Off-road mode warning lamp
6Audible warning speaker
7Instrument pack
8SLS warning lamp
9Fusible link 9
10SLS relay
11Air supply unit12RH air valve
13LH air valve
14Exhaust valve
15Diagnostic socket
16Off-road mode switch
17SLS remote handset
18Body Control Unit (BCU)
19Door switches
20SLABS ECU
21Engine Control Module (ECM)

REAR SUSPENSION
64-12 DESCRIPTION AND OPERATION
Description - SLS
General
The Self Levelling Suspension (SLS) system is an optional fitment and comprises an Electronic Control Unit (ECU),
air supply unit, two air springs and two height sensors. The SLS system only operates on the rear suspension and is
designed to keep the vehicle level to compensate for uneven loads or when towing. The system controls the gap
between the chassis and the rear axle to a tolerance of
± 0.5 mm (0.02 in). The ride height of the rear of the vehicle
can be controlled in three modes of operation; normal ride height, Off-Road Mode (ORM) and extended mode. A
transportation mode, initiated using TestBook, is also available for moving the vehicle on a trailer.
The system is controlled electronically by an ECU which is shared with the ABS system and known as the Self
Levelling and Anti-Lock Braking System (SLABS) ECU. The system operates by using an air supply unit to inflate or
deflate the air springs to maintain a constant ride height.
An accessory remote handset is available to remotely operate the SLS system to allow easier connection and
disconnection of trailers.
Two SLS system warning lamps are located in the instrument pack. The warning lamp in the bottom left corner of the
instrument pack is the SLS warning lamp. If a fault is detected in the system, the warning lamp will illuminate
continuously in an amber colour. The warning lamp also flashes in an amber colour when the remote handset is being
used. The second warning lamp, located in the top right of the instrument pack is the ORM warning lamp. When ORM
is selected the warning lamp is continuously illuminated in an amber colour. When the SLS is between standard ride
height and ORM or in extended mode, the warning lamp will flash. Standard ride height, measured between the tip of
the axle bump stop rubber and the axle, is 61.5 mm (2.42 in). ORM ride height, measured between the tip of axle
bump stop and the axle, is 100 mm (3.93 in).
A switch is located in the group of six switches on the fascia and is used to select the ORM. The switch is non-latching
and must be depressed for a minimum of 0.5 seconds to signal the ECU that ORM has been requested.

REAR SUSPENSION
DESCRIPTION AND OPERATION 64-15
Height sensors
1Spacer
2Link end
3Link
4Link end
5Arm
6Sensor body
Two height sensors are located on the outside of each chassis longitudinal forward of the rear axle. Each sensor body
is attached to a fabricated bracket and secured with two screws. The sensor is attached to the top of each radius arm
by an arm, a link and two link ends. The link ends allow articulation of the arm to allow for suspension travel. The lower
link arm is attached to a lug of the top of the radius arm and is secured with a bolt and locknut.
The sensor body and arm are manufactured from moulded nylon. The two link ends are made from natural rubber
and the link is made from mild steel. The rubber link ends allow flexibility of the arm and resistance to damage.
Each sensor is connected to the main chassis harness by a multiplug. The three pin multiplug provides an earth, a 5
V supply voltage and an output signal voltage to the SLABS ECU.
Each sensor operates on the Hall effect principle. A magnet is attached to the shaft and rotates with movement of the
arm. The magnetic flux generated acts on a Hall effect sensor and depending on its position varies the current across
the sensor. This current is measured and amplified and passed to the SLABS ECU as a linear output voltage signal,
which varies depending on the angular position of the sensor. The signal information is processed and the ECU can
determine the vehicle height.
When the sensors are replaced or removed for any reason, a calibration procedure is required to recalibrate the
sensors and the SLABS ECU. The calibration procedure requires the use of TestBook and calibration blocks to set
the axle to chassis height to a known value.
If faults occur with the height sensors, fault codes are stored in the SLABS ECU. The current and past fault codes can
be retrieved with TestBook.

REAR SUSPENSION
64-18 DESCRIPTION AND OPERATION
The ECU supplies a 5 V current to each of the height sensors. Each height sensor uses the current to supply an
analogue input to the ECU. The ECU can calculate from the input received from each height sensor the height of the
vehicle and can then power the air supply unit as necessary to raise or lower one or both air springs to level the
vehicle.
When SLS compressor operation is required, the ECU provides a battery supply to energise the SLS relay located in
the engine compartment fusebox. When the relay contacts close, a 12 V supply passes through fusible link 9 in the
engine compartment fusebox, through the relay contacts and operates the air supply unit compressor. The ECU will
then supply power to operate one or both air control valve solenoids and/or the exhaust valve solenoid to inflate or
deflate the air springs as required. The compressor does not need to be powered to deflate the air springs.
The ECU also controls the operation of the SLS audible warning, the SLS warning lamp and the ORM warning lamp.
When the ignition is switched to position II, the ECU performs a three second bulb check and illuminates the SLS and
ORM warning lamps in the instrument pack to check for operation. When the system is operating or a fault is sensed
by the ECU, the ECU will operate the appropriate warning lamp and audible warning as required. The audible warning
is operated by the Body Control Unit (BCU) when it receives a signal from the SLABS ECU. The audible warning is
emitted from a speaker at the rear of the instrument pack.
Depressing the ORM switch for a minimum of 0.5 seconds, completes an earth which the ECU uses as a signal to
initiate the ORM if conditions allow. When the ECU starts ORM, the same earth that was completed by the ORM
switch is pulled to earth by the ECU to activate the ORM warning lamp. The ECU checks for a further operation of the
ORM switch by continuously and very quickly removing the earth for the ORM warning lamp. If the ORM switch is
operated for more than 0.5 seconds, the ECU will detect this and de-activate the ORM.
The SLS part of the SLABS ECU also uses the road speed data generated within the SLABS ECU by the ABS system.
Operation of ORM and extended mode are road speed sensitive and use the ABS signal to monitor the vehicle speed.
When the accessory remote handset is used for the SLS lower and raise functions, the handset transmits RF signals
which are received by the same RF receiver used for the alarm/remote door locking system. The RF receiver passes
this data as a 25 Hz PWM signal to the BCU. The BCU then transmits this data to the SLABS ECU as raise or lower
data. TestBook is required to program the BCU for remote handset operation.
SLABS ECU connector pin details
Connector/Pin No. Description Input/Output
C0504
1 Battery supply Input
2 Ignition supply Input
5 K line (diagnostics) Input/Output
12 EarthInput
C0654
1 Left height sensor supply Output
2 Left height sensor earth Input
3 Left height sensor signal Input
4 Right height sensor supply Output

REAR SUSPENSION
DESCRIPTION AND OPERATION 64-19
Failure modes
Failures are indicated by the SLS warning lamp in the bottom left corner of the instrument pack illuminating
continuously in an amber colour. The following tables show the type of system failures and their effects on the system
operation.
Height sensors
Door Switch Inputs
SLS off-road mode switch
Air supply unit air control valves
Air supply unit compressor
5 Right height sensor earth Input
6 Right height sensor signal Input
C0655
1 Driver's door switch Input
2 Passenger and tail door switches Input
3 Left air valve Output
4 Right air valve Output
5 Exhaust valve Output
6 Air compressor (SLS relay) Output
7 Audible warning Output
8 SLS warning lamp Output
11 ORM switch/ORM warning lamp Input/Output
12 Remote handset raise/lower signal Input
Connectors and pins not listed are either not used or used by the brakes system.

+ BRAKES, DESCRIPTION AND OPERATION, Description.
Failure Effect
Sensor output stuck at 5 V Vehicle will not level
Sensor output stuck at 0 V Vehicle will not level
Mechanical link between radius arm and sensor broken Vehicle will not level
Failure Effect
Harness leads for open doors are are broken or shorted to
V Batt.Air suspension levels when one or more doors are open
Harness leads to door(s) shorted to earth Air suspension will not level
Failure Effect
Fault in wiring harness Off-road mode cannot be selected
Failure of off-road mode switch Off-road mode is activated when switch has not been
selected
Failure Effect
Valves open or short circuit Vehicle does not level or levels unevenly
Failure Effect
Faulty relay, harness fault or compressor fault Vehicle does not level upwards

REAR SUSPENSION
64-20 DESCRIPTION AND OPERATION
Operation
Circuit diagram
1SLABS ECU
2Exhaust valve
3Restrictor
4Pressure limiting valve
5Silencer
6Inlet air filter
7Compressor
8Air dryer9Non-return valve
10RH air control valve
11RH air spring
12RH height sensor
13LH height sensor
14LH air spring
15LH air control valve
The SLS system is active when the ignition switch is in position II, when one or more doors are open and for up to
thirty minutes after all doors have been closed. If the rear axle is articulated by more than 100 mm (3.93 in), the ECU
will not activate the SLS system.
The air supply unit compressor will only operate to raise the rear of the vehicle when the engine is running, with the
exception of the remote handset operation which does not require the engine running. Three modes of SLS operation
are available; Normal Ride Height, Off-Road Mode (ORM) and Extended Mode. A fourth mode, transportation mode,
is programmed by TestBook for transport or recovery of the vehicle on a trailer.

REAR SUSPENSION
REPAIRS 64-25
REPAIRS
Wheel hub
$% 64.15.01
Models with SLS:
WARNING: Ensure the air suspension system is
made safe before commencing work. Otherwise
the chassis may lower onto the bump stops
during repair.
Remove
1.Raise rear of vehicle.
WARNING: Do not work on or under a
vehicle supported only by a jack. Always
support the vehicle on safety stands.
2.Remove road wheel.
3.Release stake in drive shaft nut.
4.With an assistant depressing the brake pedal,
remove and discard drive shaft nut.
5.Remove rear brake disc.

+ BRAKES, REPAIRS, Brake disc -
rear.6.Disconnect ABS sensor multiplug.
7.Release harness from brake hose and hose
bracket.
8.Remove 4 bolts securing wheel hub to axle.
9.Release and remove wheel hub and drive shaft
assembly from axle. Remove and discard 'O'
ring from wheel hub.

REAR SUSPENSION
64-26 REPAIRS
10.Position the wheel hub and drive shaft on a
press, place supports beneath the wheel studs
and press the drive shaft from the wheel hub.Refit
1.Clean drive shaft splines, wheel hub and axle
mating faces, ABS sensor and sensor recess.
2.Fit drive shaft to axle casing.
3.Lubricate new bearing hub 'O' ring with clean
differential oil.

+ CAPACITIES, FLUIDS AND
LUBRICANTS, Lubrication.
4.Fit 'O' ring to wheel hub.
5.Apply a 3 mm (0.125 in) wide bead of Loctite
640 around drive shaft circumference as
illustrated.
6.Fit wheel hub to drive shaft and align to axle.
The Loctite will smear along the length of the
splines as the wheel hub is fitted to the drive
shaft.
7.Fit bolts securing wheel hub to axle and tighten
to 100 Nm (74 lbf.ft).
8.Fit new drive shaft nut and lightly tighten.
9.Fit rear brake disc.

+ BRAKES, REPAIRS, Brake disc -
rear.
10.With an assistant depressing the brake pedal,
tighten drive shaft nut to 490 Nm (360 lbf.ft).
Stake drive shaft nut. The drive shaft nut
must be tightened before the Loctite has
cured.
11.Connect ABS sensor multiplug and secure
harness to harness bracket and brake hose.
12.Fit road wheel and tighten nuts to 140 Nm (103
lbf.ft).
13.Remove stand(s) and lower vehicle.
M51 0057
M51 0058

REAR SUSPENSION
REPAIRS 64-27
Road spring - rear
$% 64.20.01
Remove
1.Raise rear of vehicle.
WARNING: Do not work on or under a
vehicle supported only by a jack. Always
support the vehicle on safety stands.
2.Support vehicle under chassis.
3.Remove road wheel.
4.Support weight of axle on a jack.
5.Remove bolt securing damper to axle.
WARNING: Make sure the axle cannot move
when the damper is disconnected. The
damper limits the downward movement of
the axle. If the axle is not restrained,
disconnecting the damper will allow
unrestricted movement which may cause
personal injury or damage to equipment.
6.Remove clip securing brake pipe to bracket. 7.Release ABS sensor lead from bracket.
8.Lower axle on jack and remove spring.
Refit
1.Ensure spring seats are clean.
2.Fit spring with close coil uppermost.
3.Ensure spring is correctly located on spring
seats and raise axle. Fit and tighten bolt
securing damper to axle to 124 Nm (91 lbf.ft).
4.Fit clip to secure brake pipe to bracket.
5.Fit ABS sensor lead to bracket.
6.Fit road wheel and tighten nuts to 140 Nm (103
lbf.ft).
7.Remove stand(s) and lower vehicle.

REAR SUSPENSION
REPAIRS 64-29
Damper - rear
$% 64.30.02
Remove
1.Raise rear of vehicle and support under
chassis.
WARNING: Do not work on or under a
vehicle supported only by a jack. Always
support the vehicle on safety stands.
2.Remove road wheel.
3.Support weight of axle on a jack.
4.Remove 2 bolts securing damper to axle and
chassis.
WARNING: Make sure the axle cannot move
when the damper is disconnected. The
damper limits the downward movement of
the axle. If the axle is not restrained,
disconnecting the damper will allow
unrestricted movement which may cause
personal injury or damage to equipment.
5.Compress damper and remove from vehicle.
Refit
1.Locate damper in axle and fit lower bolt, extend
damper to chassis and fit top bolt.
2.Tighten damper bolts to 125 Nm (92 lbf.ft).
3.Lower axle and remove jack.
4.Fit road wheel and tighten nuts to 140 Nm (103
lbf.ft).
5.Remove stand(s) and lower vehicle.
Bushes - radius arm
$% 64.35.29
Models with SLS:
WARNING: Ensure the air suspension system is
made safe before commencing work. Otherwise
the chassis may lower onto the bump stops
during repair.
Remove
1.Raise rear of vehicle.
WARNING: Do not work on or under a
vehicle supported only by a jack. Always
support the vehicle on safety stands.
2.Remove road wheel(s).
3. Models with SLS: Remove nut and bolt
securing height sensor link to radius arm.
4.Remove nut and bolt securing radius arm to
chassis.
5.Remove nuts securing radius arm to axle.
Remove rear bolt and lower radius arm.
Remove front bolt and remove radius arm.