1999 LAND ROVER DISCOVERY ESP

REAR SUSPENSION
64-14 DESCRIPTION AND OPERATION
The compressor is attached with Allen bolts to the motor housing and sealed with an O-ring. Attached to the
compressor is the air dryer which contains a silicate box for removing moisture from the compressed air. Air supplied
to inflate the air springs passes through the air dryer. When the air springs are deflated, the exhaust air also passes
through the air dryer, removing the moisture from the unit and expelling it to atmosphere.
Attached to end of the air dryer unit is the pressure limiting valve. The valve protects the air springs from over inflation.
The pressure limiting valve also operates when the exhaust valve is opened. The valve is pneumatically operated,
responding to air pressure applied to it.
The exhaust valve is also located with the pressure limiting valve. The exhaust valve is solenoid operated by the ECU
and directs air from the air springs and control valves to atmosphere when required.
The two air control valves for the LH and RH air springs are located at the forward end of the housing. Each valve is
connected to the compressor/air dryer unit through a shared single pipe which directs air to and from the air springs.
Each control valve is individually operated by the ECU.
All air connections to and from the air supply unit are made through the SLS air harness which is located along the
left hand chassis longitudinal.
If faults occur with the air supply unit, fault codes are stored in the SLABS ECU. These fault codes cover the
compressor power supply and the LH and RH air control valves and the exhaust valve. The current and past fault
codes can be retrieved with TestBook. TestBook can also be used to operate the compressor and the valves for
diagnostic purposes.
Air intake filter
The air intake filter is located in the left hand 'E' post, behind the tail lamp assembly. The filter comprises a plastic
moulded housing which contains two filters of differing density to remove particulate matter from the air drawn in by
the compressor. The air intake filter has a pipe which is connected to the SLS air harness by a quick release
connector. The air intake filter must be replaced as an assembly.
Air intake/Exhaust silencer
The air intake/exhaust silencer is located on the outside of the left hand chassis longitudinal, behind the air supply
unit. The silencer is an integral part of the SLS air harness and cannot be serviced individually.
The intake and exhaust air to and from the compressor passes through the silencer. The plastic moulded silencer has
two chambers. One chamber reduces system exhaust noise and the other dampens intake air pulses produced by
the compressor.

REAR SUSPENSION
DESCRIPTION AND OPERATION 64-17
SLABS ECU
1SLABS ECU
2Bracket
3BCU (Ref. only)4ACE ECU (Ref. only)
5Attachment nuts
The SLABS ECU is mounted on a bracket behind the passenger glove box and is identified from the other ECU's by
its five connectors. The five connectors are located on the lower face of the ECU and mate with five connectors from
the main harness. The twelve, six and eighteen pin connectors are used to supply inputs and outputs to and from the
ECU. The remaining connectors are used for the ABS operation.

+ BRAKES, DESCRIPTION AND OPERATION, Description.
The SLABS ECU receives a continuous battery supply from fuse 11 in the engine compartment fusebox. An ignition
'ON' signal is supplied from the ignition switch via fuse 28 in the passenger compartment fusebox. The ECU has the
ability to control when it requires power and is not reliant on the ignition signal for it to power up.
The ECU incorporates a counter which times the operation of the SLS system and prevents the compressor
exceeding its duty cycle. The ECU can remain powered for up to 1.5 hours after ignition off is sensed to allow the
counter to continue running to avoid an ignition cycle resetting the counter.
Opening any of the doors will power up the ECU, irrespective of ignition switch position. The door open signal is
sensed by the door switch completing an earth path which is sensed by the ECU. The ECU cannot differentiate
between any of the doors. The door open signal powers the ECU for up to 30 minutes to allow the vehicle to re-level
when a load is removed or passengers leave the vehicle.
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.

REAR SUSPENSION
64-22 DESCRIPTION AND OPERATION
Off-road mode (ORM)
ORM is used to raise the rear of the vehicle from normal ride height to the ORM ride height of 100 mm between the
tip of the bump stop and the axle.
ORM is activated by depressing the ORM switch located on the fascia for not less than 0.5 seconds. With the engine
running, all doors closed and the vehicle speed below 18 mph (30 km/h), the audible warning will sound once and the
ORM warning lamp in the instrument pack will start to flash when the switch is released. The compressor will be
started and the air control valves will be energised by the ECU to inflate the air springs and raise the rear of the vehicle.
When the full ORM height is reached, the ECU will terminate compressor operation and close the air valves. The ORM
warning lamp will stop flashing and remain continuously illuminated to inform the driver that the SLS system is in ORM.
When ORM is no longer required, depressing the ORM switch for not less than 0.5 seconds with all doors closed will
lower the SLS to normal ride height. The audible warning will sound once and the ORM warning lamp will flash as the
suspension lowers. The ECU energises the air control valves and the exhaust valve to release air pressure from the
air springs. When standard ride height is reached the ORM warning lamp will extinguish and the ECU will de-energise
the air control valves and the exhaust valve solenoids.
If the SLS is in ORM and the vehicle speed exceeds 18 mph (30 km/h), the ECU will lower the SLS to standard ride
height. The driver will be informed of this by an audible warning and the ORM warning lamp flashing as the suspension
lowers. When normal ride height is achieved, the ORM warning lamp will extinguish.
At sea level, the time to change the SLS from normal ride height to ORM or visa versa will take between 15 and 20
seconds.
If the ECU determines that conditions are not correct for SLS operation, i.e.; axle articulation or system fault, the
audible warning will sound three times to inform the driver that the ORM request has not been granted.
Extended mode
The extended mode is automatically operated by the ECU and requires no input from the driver. Extended mode
operates when the chassis is grounded causing the rear wheels to spin. This information is generated by the ABS
function of the SLABS ECU.
When the ECU senses that the chassis is grounded and the vehicle speed is less than 6 mph (10 km/h), the ECU will
operate the compressor and energise the air control valves for 25 seconds to raise the rear of the vehicle. This
operates irrespective of the mode that the SLS system is in at that time. To inform the driver, the ORM warning lamp
will flash continuously at all times that the system is in extended mode.
The driver can exit the extended mode by depressing the ORM switch for not less than 0.5 seconds or by exceeding
8 mph (13 km/h).
Remote handset SLS control
The remote handset is an accessory item which allows the SLS to be operated between normal ride height and bump
stop height to allow easier connection and disconnection of trailers. The remote handset is similar in appearance to
that of the remote door locking handset but does not have an integral key. A circular button with an arrow is used to
raise the SLS and an oval button with the 'Land Rover' logo is used to lower the SLS.
The remote handset control requires all doors to be closed and the ignition to be in position II, but the engine does
not need to be running.
Pressing the lower button will signal the SLABS ECU, via the RF receiver and the BCU, to energise the exhaust valve
and air control valves. The SLS will lower up to 60 mm (2.36 in) below normal ride height if the button is held. If the
button is released the SLS will stop at that point.
Pressing the raise button will signal the SLABS ECU, via the RF receiver and the BCU, to start the compressor and
energise the exhaust valve and air control valves. The SLS will raise to normal ride height if the button is held. If the
button is released the SLS will stop at that point.
When raising or lowering the SLS using the remote handset, the SLS warning lamp will flash and the audible warning
will sound when the system is operating. When the SLS is fully lowered the warning lamp will stay illuminated. The
SLS will reset to normal ride height if the vehicle speed exceeds 3 mph (5 km/h) for 10 seconds when the SLS is
lowered.

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 70-21
ETC
The ETC function uses brake intervention to prevent wheel spin and maintain even torque distribution to the wheels.
ETC is automatically enabled while the brakes are off at speeds up to 62.5 mph (100 km/h), and operates the brakes
either individually or in axle pairs:
lAt speeds up to 31.3 mph (50 km/h), ETC uses individual brake intervention to maintain even torque distribution
between wheels on the same axle.
lVehicles up to 03 model year – At speeds between 0 and 62.5 mph (0 and 100 km/h), ETC also uses brake
intervention in axle pairs to maintain even torque distribution between the front and rear axles. In effect, this mode
of operation replaces the centre differential lock of the transfer box which, although still incorporated, is non
operational under normal driving conditions.

+ TRANSFER BOX - LT230SE, DESCRIPTION AND OPERATION, Description. If the centre differential
lock is in the locked condition, the SLABS ECU illuminates the ABS and ETC warning lamps and inhibits the ETC
function (the ABS, EBD and HDC functions are retained, but at degraded performance levels).
lVehicles from 03 model year (with differential lock fitted) – At speeds between 0 and 62.5 mph (0 and 100
km/h), ETC uses brake intervention in axle pairs to maintain even torque distribution between the front and rear
axles. If the centre differential lock is in the locked condition, the differential lock warning lamp in the instrument
pack is illuminated. The ABS, EBD, ETC and HDC functions are retained, but with revised parameters to suit the
locked differential.
While the ETC function is enabled, if the SLABS ECU detects a wheel accelerating faster than the average, indicating
loss of traction, it operates the ABS modulator in the active braking mode. Depending on the vehicle speed, active
braking is employed for either the brake of the affected wheel or for both brakes on the affected axle, until all four
wheels are driven at approximately the same speed again. During active braking the SLABS ECU also illuminates the
ETC warning lamp, for a minimum of 2 seconds or for the duration that ETC is active. ETC operation is desensitised
during 'hard' cornering.
HDC
HDC uses brake intervention to provide a controlled descent ability in off road conditions when engine braking is
insufficient to maintain a comfortable speed. This allows the driver to leave HDC selected and to control the vehicle's
descent speed, down to the system's minimum target speed, using only the accelerator pedal. The HDC function is
selected on/off by a switch on the fascia. When selected on, HDC is enabled in all forward gears and reverse provided:
lVehicle speed is below 31.3 mph (50 km/h).
lThe transfer box is in low range.
lOn manual gearbox vehicles, the clutch is engaged.
When HDC is enabled, the HDC information warning lamp illuminates. If HDC is selected outside the above
conditions, the HDC information warning lamp flashes and the audible warning sounds continuously.
When HDC is enabled, the SLABS ECU calculates a target speed from the throttle position element of the engine data
input, and compares this with actual speed. If the actual speed is higher than the target speed, the SLABS ECU
operates the ABS modulator in the active braking mode to slow the vehicle down to the target speed. While the braking
force is being applied, the SLABS ECU also energizes the brake lamp relay to put the brake lamps on. Active braking
is discontinued while vehicle speed is below the target speed or if the foot brakes are applied. Applying the foot brakes
during active braking may result in a pulse through the brake pedal, which is normal.
During active braking, the brakes are operated predominantly on the wheels of the leading axle, but if that is not
sufficient to achieve the required deceleration the brakes of the trailing axle are also applied. The deceleration rate is
dependent on the speed differential between initial vehicle speed and the target speed. The deceleration rates are
relatively low at higher speed differentials, then progressively increase as vehicle speed approaches the target speed.
Anti-lock braking is also enabled during active braking, but at very low speeds some wheel lock can occur.
The target speed increases as the accelerator pedal is pressed, from a programmed minimum with the accelerator
pedal released, up to a maximum of 31.3 mph (50 km/h). For any given accelerator pedal position, while travelling
uphill or on level ground the target speed is always greater than the corresponding vehicle speed, which allows the
vehicle to be driven normally without HDC intervention. However, when travelling downhill, the gravitational effect on
the vehicle means that for any given accelerator pedal position the target speed is less than the corresponding vehicle
speed, and HDC intervenes to limit vehicle speed to the target speed.

CORROSION PREVENTION AND SEALING
CORROSION PREVENTION 77-4-7
The checks described above are intended to be visual only. It is not intended that the operator should remove trim
panels, finishers, rubbing strips or sound-deadening materials when checking the vehicle for corrosion and paint
damage.
With the vehicle on a lift, and using an inspection or spot lamp, visually check for the following:
lCorrosion damage and damaged paintwork, condition of underbody sealer on front and rear lower panels, sills
and wheel arches;
lDamage to underbody sealer. Corrosion in areas adjacent to suspension mountings and fuel tank fixings.
NOTE: The presence of small blisters in the underbody sealer is acceptable, providing they do not expose bare metal.
Pay special attention to signs of damage caused to panels or corrosion protection material by incorrect jack
positioning.
WARNING: It is essential to follow the correct jacking and lifting procedures.
With the vehicle lowered, visually check for evidence of damage and corrosion on all visible painted areas, in
particular the following:
lFront edge of bonnet;
lVisible flanges in engine compartment;
lLower body and door panels.
Rectify any bodywork damage or evidence of corrosion found during inspection as soon as is practicable, both to
minimise the extent of the damage and to ensure the long term effectiveness of the factory-applied corrosion
prevention treatment. Where the cost of rectification work is the owner's responsibility, the Dealer must advise the
owner and endorse the relevant documentation accordingly.
Where corrosion has become evident and is emanating from beneath a removable component (e.g. trim panel,
window glass, seat etc.), remove the component as required to permit effective rectification.
Underbody protection repairs
Whenever body repairs are carried out, ensure that full sealing and corrosion protection treatments are reinstated.
This applies both to the damaged areas and also to areas where protection has been indirectly impaired, as a result
either of accident damage or repair operations.
Remove corrosion protection from the damaged area before straightening or panel beating. This applies in particular
to panels coated with wax, PVC underbody sealer, sound deadening pads etc.
WARNING: DO NOT use oxy-acetylene gas equipment to remove corrosion prevention materials. Large
volumes of fumes and gases are liberated by these materials when they burn.
NOTE: Equipment for the removal of tough anti-corrosion sealers offers varying degrees of speed and effectiveness.
The compressed air-operated scraper (NOT an air chisel) offers a relatively quiet mechanical method using an
extremely rapid reciprocating action. Move the operating end of the tool along the work surface to remove the material.
The most common method of removal is by means of a hot air blower with integral scraper.
Another tool, and one of the most efficient methods, is the rapid-cutting 'hot knife'. This tool uses a wide blade and is
quick and versatile, able to be used easily in profiled sections where access is otherwise difficult.
Use the following procedure when repairing underbody coatings:
1Remove existing underbody coatings
2After panel repair, clean the affected area with a solvent wipe, and treat bare metal with an etch phosphate
material
3Re-prime the affected area
CAUTION: DO NOT, under any circumstances, apply underbody sealer directly to bare metal surfaces.
4Replace all heat-fusible plugs which have been disturbed. Where such plugs are not available use rubber
grommets of equivalent size, ensuring that they are embedded in sealer
5Mask off all mounting faces from which mechanical components, hoses and pipe clips, have been removed.
Underbody sealer must be applied before such components are refitted
6Brush sealer into all exposed seams
7Spray the affected area with an approved service underbody sealer
8Remove masking from component mounting faces, and touch-in where necessary. Allow adequate drying time
before applying underbody wax

CORROSION PREVENTION AND SEALING
77-4-8 CORROSION PREVENTION
After refitting mechanical components, including hoses and pipes and other fixtures, mask off the brake discs and
apply a coat of approved underbody wax.
NOTE: Where repairs include the application of finish paint coats in the areas requiring underbody wax, carry out paint
operations before applying wax.
Cavity wax injection
Areas treated with cavity wax are shown in the previous figures. After repairs, always re-treat these areas with an
approved cavity wax. In addition, treat all interior surfaces which have been disturbed during repairs whether they
have been treated in production or not. This includes all box members, cavities and door interiors. It is permissible to
drill extra holes for access where necessary, provided these are not positioned in load-bearing members. Ensure that
such holes are treated with a suitable zinc rich primer, brushed with wax and then sealed with a rubber grommet.
Before wax injection, ensure that the cavity to be treated is free from any contamination or foreign matter. Where
necessary, clear out any debris using compressed air.
Ensure that cavity wax is applied AFTER the final paint process and BEFORE refitting any trim components.
During application, ensure that the wax covers all flange and seam areas and that it is adequately applied to all
repaired areas of both new and existing panels.
It should be noted that new panel assemblies and complete body shells are supplied without wax injection treatment.
Ensure that such treatment is carried out after repairs.
Effective cavity wax protection is vital. Always observe the following points:
lComplete all paint refinish operations before wax application;
lClean body panel areas and blow-clean cavities if necessary, before treatment;
lMaintain a temperature of 18° C (64° F) during application and drying;
lCheck the spray pattern of injection equipment;
lMask off all areas not to be wax coated and which could be contaminated by wax overspray;
lRemove body fixings, such as seat belt retractors, if contamination is at all likely;
lMove door glasses to fully closed position before treating door interiors;
lTreat body areas normally covered by trim before refitting items;
lCheck that body and door drain holes are clear after the protective wax has dried;
lKeep all equipment clean, especially wax injection nozzles.
Underbody wax
The underbody wax must be reinstated following all repairs affecting floor panels. The wax is applied over paints and
underbody sealers.
Remove old underbody wax completely from a zone extending at least 200 mm (7.874 in) beyond the area where new
underbody sealer is to be applied.
Engine bay wax
Reinstate all protective engine bay wax disturbed during repairs using an approved material.
Where repairs have involved replacement of engine bay panels, treat the entire engine compartment including all
components, clips and other fixtures with an approved underbonnet lacquer or wax.

+ BODY SEALING MATERIALS, MATERIALS AND APPLICATIONS, Approved materials.

HEATING AND VENTILATION
DESCRIPTION AND OPERATION 80-13
Operation
Air distribution
Turning the distribution knob on the control panel turns the control flaps in the heater assembly to direct air to the
corresponding fascia and footwell outlets.
Air temperature
Turning the LH or RH temperature knob on the control panel turns the related blend flaps in the heater assembly. The
blend flaps vary the proportion of air going through the cold air bypass and the heater matrix. The proportion varies,
between full bypass no heat and no bypass full heat, to correspond with the position of the temperature knob.
Blower speed
The blower can be selected off or to run at one of four speeds. While the ignition is on, when the blower switch is set
to positions 1, 2, 3, or 4, ignition power energises the blower relay, which supplies battery power to the blower. At
switch positions 1, 2 and 3, the blower switch also connects the blower to different earth paths through the resistor
pack, to produce corresponding differences of blower operating voltage and speed. At position 4, the blower switch
connects an earth direct to the blower, bypassing the resistor pack, and full battery voltage drives the blower at
maximum speed.
Fresh/Recirculated inlet air
When the recirculated air switch is latched in, the amber indicator LED in the switch illuminates and an earth is
connected to the recirculated air side of the fresh/recirculated air servo motor. The fresh/recirculated air servo motor
then turns the control flaps in the air inlet duct to close the fresh air inlet and open the recirculated air inlets.
When the latch of the recirculated air switch is released, the amber indicator LED in the switch extinguishes and the
earth is switched from the recirculated air side to the fresh air side of the fresh/recirculated air servo motor. The fresh/
recirculated air servo motor then turns the control flaps in the air inlet duct to open the fresh air inlet and close the
recirculated air inlets.
FBH system (where fitted)
The FBH system operates only while the engine is running and the ambient temperature is less than 5 °C (41 °F).
With the engine running and the ambient temperature below 5 °C (41 °F), the air temperature sensor connects the
alternator power supply to the ECU in the FBH unit. On receipt of the alternator power supply, the ECU starts the
circulation pump and, depending on the input from the temperature sensor in the heat exchanger, enters either a
standby or active mode of operation. If the heat exchanger casing temperature is 65 °C (149 °F) or above, the ECU
enters a standby mode of operation. If the heat exchanger casing temperature is below 65 °C (149 °F), the ECU enters
an active mode of operation. In the standby mode, the ECU monitors the heat exchanger casing temperature and
enters the active mode if it drops below 65 °C (149 °F). In the active mode, the ECU initiates a start sequence and
then operates the system at full or part load combustion to provide the required heat input to the coolant.
Start sequence
At the beginning of the start sequence the ECU energises the glow plug function of the glow plug/flame sensor, to
preheat the combustion chamber, and starts the combustion air fan at slow speed. After 30 seconds, the ECU
energises the FBH fuel pump at the starting sequence speed. The fuel delivered by the FBH fuel pump evaporates in
the combustion chamber, mixes with air from the combustion air fan and is ignited by the glow plug/flame sensor. The
ECU then progressively increases the speed of the FBH fuel pump and the combustion air fan to either part or full
load speed, as required by the system. Once full or part load speed is achieved, the ECU switches the glow plug/flame
sensor from the glow plug function to the flame sensing function to monitor combustion. From the beginning of the
start sequence to stable combustion takes approximately 90 seconds for a start to part load combustion and 150
seconds for a start to full load combustion.