towing LAND ROVER DISCOVERY 1999 User Guide

AUTOMATIC GEARBOX - ZF4HP22 - 24
44-18 DESCRIPTION AND OPERATION
Kickdown
The EAT ECU monitors the input of the throttle position sensor to determine when kickdown is required. When it
detects a kickdown situation, the EAT ECU immediately initiates a down shift provided the target gear will not cause
the engine speed limit to be exceeded.
Torque converter lock-up
The EAT ECU energises the lock-up solenoid valve to engage the lock-up clutch. Lock-up clutch operation is
dependent on throttle position, engine speed, operating mode and the range selected on the transfer box.
High range
Unique lock-up maps, similar to the shift maps, are incorporated in the economy and sport modes for all forward gears.
Engagement and disengagement of the lock-up clutch is dependent on throttle position and engine speed.
Low range
To enhance off road control, particularly when manoeuvring at low speeds, torque converter lock-up does not occur
when there is any degree of throttle opening. When the throttle is closed above a preset engine speed, the lock-up
clutch engages to provide maximum engine braking.
Increased load/reduced torque compensation
To aid performance and driveability in the high range economy mode, the EAT ECU has three adaptive shift and lock-
up maps. These maps delay upshifts and torque converter lock-up similar to the sport mode if the inputs from the
engine indicate:
lA sustained high load on the engine, such as occurs when the vehicle is ascending a steep gradient or towing a
trailer.
lA lower than normal engine torque, such as occurs at altitude or high ambient temperatures.
The EAT ECU monitors the engine inputs and selects the most appropriate adaptive map for the prevailing conditions.
Diagnostics
While the ignition is on, the EAT ECU diagnoses the system for faults. The extent of the diagnostic capability at any
particular time depends on the prevailing operating conditions, e.g. it is not possible to check torque converter lock-
up while the vehicle is stationary, or to check for a short circuit to earth if the circuit concerned is already at a low
potential.
If a fault is detected, the EAT ECU immediately stores a fault code and the values of three operating parameters
associated with the fault. Depending on the fault, there are four possible effects:
lThe fault has little effect on gearbox operation or vehicle emissions. The driver will probably not notice any
change and the warning lamps remain extinguished.
lThe fault has little effect on gearbox operation but may effect vehicle emissions. On NAS vehicles, if the fault is
detected on a second consecutive drive cycle, the MIL illuminates.
lAll gears are available but kickdown does not function. The sport and manual warning lamps flash. The MIL
remains extinguished.
lLimp home mode is selected and vehicle performance is greatly reduced. The sport and manual warning lamps
flash. In all markets, if the fault is detected on a second consecutive drive cycle, the MIL illuminates.
After the detection of a fault, the effects remain active for the remainder of the drive cycle. In subsequent drive cycles,
as soon as the EAT ECU diagnoses the fault is no longer present, it resumes normal control of the gearbox. The
conditions required to diagnose that the fault is no longer present depend on the fault. Some faults require the engine
to be started, others require only that the ignition is switched on.
After a fault has not recurred for forty warm-up cycles, the fault is deleted from the EAT ECU memory. Only five
different faults can be stored in the memory at any one time. If a further fault occurs, the fault with the lowest priority
will be replaced by the new fault.
Mechanical limp home
In the mechanical limp home mode, gear engagement is controlled by the manual valve. The gearbox is fixed in 4th
gear if the fault occurs while the vehicle is moving, or 3rd gear if the fault occurs while the vehicle is stationary. 3rd
gear is also engaged if a vehicle is brought to a stop and the selector lever is moved out of, and back into, D. Neutral
and reverse gear are also available.

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.

CORROSION PREVENTION AND SEALING
77-4-6 CORROSION PREVENTION
Corrosion prevention
Factory treatments
During production, vehicle bodies are treated with the following anti-corrosion materials:
lA PVC-based underbody sealer which is sprayed onto the underside of the main floor, rear floor, front and rear
wheelarches and the front valance assembly;
lAn application of cavity wax which is sprayed into the sill panels, 'A' post, 'B-C' post, fuel filler aperture, body rear
panel and the lower areas of the door panels;
lA coating of underbody wax which is applied to the entire underbody inboard of the sill vertical flanges, and
covers all moving and flexible components EXCEPT for wheels, tyres, brakes and exhaust;
lA coat of protective wax applied to the engine bay area.
Whenever body repairs are carried out, ensure the anti-corrosion materials in the affected area are repaired or
renewed as necessary using the approved materials.

+ BODY SEALING MATERIALS, MATERIALS AND APPLICATIONS, Approved materials.
Precautions during body repairs and handling
Take care when handling the vehicle in the workshop. Underbody sealers, seam sealers, underbody wax and body
panels may be damaged if the vehicle is carelessly lifted.

+ LIFTING AND TOWING, LIFTING.
Proprietary anti-corrosion treatments
The application of proprietary anti-corrosion treatments, in addition to the factory-applied treatment, could invalidate
the Corrosion Warranty and should be discouraged. This does not apply to Rover approved, compatible, preservative
waxes which may be applied on top of existing coatings.
Fitting approved accessories
When fitting accessories ensure that the vehicle's corrosion protection is not affected, either by breaking the protective
coating or by introducing a moisture trap.
Do not screw self-tapping screws directly into body panels. Fit suitable plastic inserts to the panel beforehand. Always
ensure that the edges of holes drilled into panels, chassis members and other body parts are protected with a suitable
zinc rich or acid etch primer, and follow with a protective wax coating brushed onto the surrounding area.
Do not attach painted metal surfaces of any accessory directly to the vehicle's bodywork unless suitably protected.
Where metal faces are bolted together always interpose a suitable interface material such as weldable zinc rich
primer, extruded strip, or zinc tape.
Steam cleaning and dewaxing
Due to the high temperatures generated by steam cleaning equipment, there is a risk that certain trim components
could be damaged and some adhesives and corrosion prevention materials softened or liquified.
Adjust the equipment so that the nozzle temperature does not exceed 90° C (194° F). Take care not to allow the steam
jet to dwell on one area, and keep the nozzle at least 300 mm (11.811 in) from panel surfaces.
DO NOT remove wax or lacquer from underbody or underbonnet areas during repairs. Should it be necessary to
steam clean these areas, apply a new coating of wax or underbody protection as soon as possible.
Inspections during maintenance servicing
It is a requirement of the Corrosion Warranty that the vehicle body is checked for corrosion by an authorised Land
Rover Dealer at least once a year, to ensure that the factory-applied protection remains effective.
Service Job Sheets include the following operations to check bodywork for corrosion:
lWith the vehicle on a lift, carry out visual check of underbody sealer for damage;
lWith the vehicle lowered, inspect exterior paintwork for damage and body panels for corrosion.
It will be necessary for the vehicle to be washed by the Dealer prior to inspection of bodywork if the customer has
offered the vehicle in a dirty condition.