ABS LAND ROVER DISCOVERY 1999 Manual Online

REAR SUSPENSION
REPAIRS 64-29
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.

BRAKES
DESCRIPTION AND OPERATION 70-1
BRAKES DESCRIPTION AND OPERAT ION
Brake system control component layout
RH drive shown, LH drive similar
1Hill descent switch
2ABS sensor3SLABS ECU

BRAKES
DESCRIPTION AND OPERATION 70-3
1ABS sensor
2ABS modulator
3Return pump relay
4SLABS ECU
5Brake lamp relay
6Centre high mounted stop lamp
7LH brake lamp
8RH brake lamp
9Instrument pack10Body control unit
11Reverse lamp switch (manual gearbox)
12Diagnostic socket
13HDC switch
14Transmission high/low switch
15Centre differential lock switch
16Engine control module
17Battery power supply
18Ignition power supply

BRAKES
70-4 DESCRIPTION AND OPERATION
Brake system hydraulic component
layout
RH drive shown, LH drive similar
1Rear brake
2ABS modulator
3Front brake
4Inlet manifold plenum (V8 models)
5Non return valve6Master cylinder assembly
7Brake fluid reservoir
8Brake servo assembly
9Vacuum pump (diesel models)

BRAKES
DESCRIPTION AND OPERATION 70-5
Description
General
The brakes consist of front and rear disc brakes operated by a diagonally split, dual circuit hydraulic system with
vacuum servo power assistance. The system incorporates the following control functions as standard on all models:
lAnti-lock Brakes (ABS), to prevent road wheels locking during brake application.
lElectronic Brake Distribution (EBD), to control distribution of hydraulic pressure between front and rear axles.
Replaces mechanical pressure limiting valve of previous systems.
lElectronic Traction Control (ETC), to maintain even torque distribution to the road wheels.
lHill Descent Control (HDC), to provide controlled descent ability in off road conditions.
Hydraulic system schematic
1Master cylinder/brake servo assembly
2Brake pedal
3ABS modulator
4Rear brake5Front brake
6Hydraulic circuit
aPrimary
bSecondary
For normal brake operation, brake pedal movement is assisted by the brake servo assembly and transmitted to the
master cylinder assembly. The master cylinder assembly converts brake pedal movement to hydraulic pressure.
Primary and secondary brake pipe circuits supply the hydraulic pressure to the brakes via the ABS modulator: the
primary circuit supplies the front left and rear right brakes; the secondary circuit supplies the front right and rear left
brakes. Vacuum for the brake servo assembly is obtained from the engine inlet manifold (V8 models) or a vacuum
pump (diesel models), through a vacuum line and non return valve. To reduce operating noise, sleeving is installed
on some of the brake pipes in the engine compartment and the pipes are located in sprung pipe clips.
For all control functions, the ABS modulator regulates the hydraulic pressure to the brakes to control the speed of all
four wheels, either individually or in axle pairs. Operation of the ABS modulator is controlled by the Self Levelling and
Anti-lock Braking Systems (SLABS) ECU. The SLABS ECU also operates warning indications in the instrument pack
to provide the driver with status information on each function.

BRAKES
DESCRIPTION AND OPERATION 70-13
ABS modulator
ABS modulator schematic
1Master cylinder/brake servo assembly
2Brake pedal
3ABS modulator
4Shuttle valve switch
5Shuttle valve
6Damper chamber
7Restrictor8Return pump
9Non return valve
10Expansion chamber
11Outlet solenoid valve
12Inlet solenoid valve
13Rear brake
14Front brake

BRAKES
70-14 DESCRIPTION AND OPERATION
The ABS modulator is a 4 channel unit that controls the supply of hydraulic pressure to the brakes in response to
inputs from the SLABS ECU. The modulator is attached by three mounting bushes to a bracket on the LH inner front
wing, and connected to the primary and secondary hydraulic circuits downstream of the master cylinder assembly.
Three electrical connectors link the ABS modulator to the vehicle wiring.
Passages within the ABS modulator, separated into primary and secondary circuits, connect to the various internal
components that control the supply of hydraulic pressure to the brakes:
lShuttle valves and non return valves control the flow through the internal circuits.
lShuttle valve switches, connected in series to the SLABS ECU, provide a brakes on/off signal.
lA damper chamber and restrictor are included in each circuit to refine system operation.
lInlet and outlet solenoid valves control the flow to the individual brakes.
lAn expansion chamber is connected to each circuit to absorb pressure.
lA return pump is connected to both circuits to provide a pressure source.
The ABS modulator has three operating modes: Normal braking, ABS braking and active braking.
Normal braking mode
When the brake pedal is pressed, pressurised fluid from the master cylinder assembly moves the shuttle valves to
open lines 'A' and close the shuttle valve switches. Pressurised fluid then flows through the open inlet solenoid valves
to operate the brakes. The closed shuttle valve switches supply a brakes on signal to the SLABS ECU. If the SLABS
ECU determines that EBD is necessary, it energises the inlet solenoid valves for the brakes of one axle. The inlet
solenoid valves close to isolate the brakes from any further increase in hydraulic pressure.
ABS braking mode
When in the normal braking mode, if the SLABS ECU determines that ABS braking is necessary, it energises the inlet
and outlet solenoid valves of the related brake and starts the return pump. The inlet solenoid valve closes to isolate
the brake from pressurised fluid; the outlet solenoid valve opens to release pressure from the brake into the expansion
chamber and the return pump circuit. The brake releases and the wheel begins to accelerate. The SLABS ECU then
operates the inlet and outlet solenoid valves to control the supply of hydraulic pressure to the brake and apply the
maximum braking effort (for the available traction) without locking the wheel.
Active braking mode
When ETC or HDC are enabled, and the SLABS ECU determines that active braking is necessary, it starts the return
pump. Hydraulic fluid, drawn from the reservoirs through the master cylinder, shuttle valves and lines 'B', is
pressurised by the return pump and supplied to lines 'A'. The SLABS ECU then operates the inlet and outlet solenoid
valves to control the supply of hydraulic pressure to the individual brakes and slow the wheel(s).

BRAKES
DESCRIPTION AND OPERATION 70-17
SLABS ECU
The SLABS ECU is attached to a bracket behind the front passenger glovebox. Brake related inputs are processed
by the SLABS ECU, which then outputs control signals to the ABS modulator. Five electrical connectors interface the
SLABS ECU with the vehicle wiring.
SLABS ECU connector pin details
Connector/Pin
No.Description Input/Output
C0504
1 Battery supply Input
2 Ignition supply Input
3 Road speed Output
4 Rough road (V8 models only) Output
5 K line (diagnostics) Input/Output
7 Reverse gear Input
8 Return pump monitor Input
9 Brake warning lamp Output
10 Engine data (throttle position, torque, engine type, gearbox type) Input
11 Transfer box range Input
12 Earth-
13 ETC warning lamp Output
14 HDC switch Input
15 Neutral selected (automatic gearbox only) Input
16 HDC fault warning lamp Output
17 HDC information warning lamp Output
18 ABS warning lamp Output
C0505
1 Front left wheel speed Input
2 Front left wheel speed Input
3 Rear right wheel speed Input
4 Front right wheel speed Input
5 Front right wheel speed Input
6 Rear right wheel speed Input
7 Rear left wheel speed Input
8 Rear left wheel speed Input
C0506
1 Front left outlet solenoid valve Output
2 Front left inlet solenoid valve Output
3Earth-
4 Front right outlet solenoid valve Output

BRAKES
70-18 DESCRIPTION AND OPERATION
The SLABS ECU continually calculates vehicle speed using the wheel speed inputs from all four ABS sensors. The
calculated vehicle speed is then used as a reference against which individual wheel speeds are monitored for
unacceptable acceleration or deceleration. The ABS sensor inputs are also used by the SLABS ECU to detect vehicle
deceleration rate, vehicle cornering rate and rough terrain.
The engaged forward gear and (on manual gearbox models) the clutch status are computed from the engine data
input, the engine speed input and vehicle speed. Reverse gear status is provided by an input from the reverse lamp
switch (manual gearbox models) or the BCU (automatic gearbox models). On automatic models, the BCU also
provides the neutral selected input.
In addition to controlling the brake related functions, the SLABS ECU:
lControls the operation of the self levelling suspension (SLS) system (where fitted).

+ REAR SUSPENSION, DESCRIPTION AND OPERATION, Description.
lOn V8 models, outputs a rough road signal to the ECM when traversing rough terrain.
lOutputs a vehicle speed signal.
The vehicle speed signal is output to the following systems (where fitted):
lActive Cornering Enhancement.

+ FRONT SUSPENSION, DESCRIPTION AND OPERATION, Description - ACE.
lAir conditioning.

+ AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.
lCruise control.

+ ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
lEngine management.

+ ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine
management.
lIn-car entertainment.

+ IN CAR ENTERTAINMENT, DESCRIPTION AND OPERATION, Description.
lInstrument pack.

+ INSTRUMENTS, DESCRIPTION AND OPERATION, Description.
5 Front right inlet solenoid valve Output
6 Shuttle valve switches Input
7 Rear left outlet solenoid valve Output
8 Rear left inlet solenoid valve Output
9 Centre differential lock switch Input
10 Rear right outlet solenoid valve Output
11 Rear right inlet solenoid valve Output
12 Brake lamp relay Output
15 Return pump relay Output
C0655
7 Audible warning Output
10 Engine speed Input
Connector and pins not listed are either not used or used by the self levelling suspension system.

+ REAR SUSPENSION, DESCRIPTION AND OPERATION, Description.
Connector/Pin
No.Description Input/Output

BRAKES
DESCRIPTION AND OPERATION 70-19
ABS sensors
The ABS sensors supply the SLABS ECU with a sinusoidal speed signal from each wheel. An inductive sensor,
installed in the hub bearing of each wheel, senses off a 60 tooth exciter ring integrated into the inner race of the hub
bearing. Each ABS sensor has a fly-lead connecting it to the vehicle wiring.
HDC switch
The HDC switch is a latching push switch installed on the fascia, in the switchpack inboard of the steering wheel.
When pushed in, the switch connects an ignition supply to the SLABS ECU to initiate HDC.
Warning indications
The SLABS ECU operates audible and visual warnings to convey brake system status.
Audible warning
A repetitive chime, at a frequency of 2 Hz, draws attention to warning lamp indications. The chime is produced on the
speaker in the instrument pack.
Warning lamps
1ABS warning lamp
2HDC fault warning lamp
3ETC warning lamp4HDC information warning lamp
5Brake warning lamp (all except NAS)
6Brake warning lamp (NAS only)
The following brake system warning lamps can be found in the instrument pack:
lA red brake graphic (all except NAS vehicles) or red BRAKE legend (NAS vehicles), to warn of low brake fluid
level, handbrake on and brake control system failure affecting EBD.
lAn amber ABS graphic, to warn of brake control system failure affecting the ABS function.
lAn amber TC graphic, to warn of brake control system failure affecting the ETC function.
lTwo inclined vehicle graphics, one amber (fault) and one green (information), to indicate operating status of HDC
and to warn of brake control system failure affecting the HDC function.
Each warning lamp is illuminated by a separate LED. The ABS, brake and ETC warning lamps are continuously on
while illuminated; the two HDC warning lamps are either continuously on or flash at a frequency of 2 Hz while
illuminated.