1999 LAND ROVER DISCOVERY clutch

AUTOMATIC GEARBOX - ZF4HP22 - 24
DESCRIPTION AND OPERATION 44-19
Fault effects and warning indications
Fault code,
OBD II
(TestBook)Fault description Effect Warning lamp
illumination
MIL Sport/
Manual
P0705
(14, 23)* Gear position switch,
incorrect outputsMaintains current gear in low range, limp
home mode in high range. Shift pressure to
maximum, harsh gear shifts/engagement.On On
P0721
(21)* Downshift safety
monitor prevented
downshift which would
have caused engine
overspeedMaintains current gear in low range, limp
home mode in high range. Shift pressure to
maximum, harsh gear shifts/engagement.On On
P0722
(22)* Torque converter
slippingMaintains current gear in low range, limp
home mode in high range. Shift pressure to
maximum, harsh gear shifts/engagement.On On
P0731
(29)* Ratio monitoring,
implausible 1st gear
ratioNo apparent effect On On
P0732
(30)* Ratio monitoring,
implausible 2nd gear
ratioNo apparent effect On Off
P0733
(31)* Ratio monitoring,
implausible 3rd gear
ratioNo apparent effect On Off
P0734
(32)* Ratio monitoring,
implausible 4th gear
ratioNo apparent effect On Off
P0741
(5)* Torque converter
lock-up clutch faultMay affect driveability. On Off
P0743
(7, 25)* Torque converter
lock-up solenoid (MV
3), open or short circuitLimp home mode in low and high ranges. Shift
pressure to maximum, harsh gear shifts/
engagement.On On
P0748
(10, 28)* Pressure regulating
solenoid (MV 4), open
or short circuitLimp home mode in low and high ranges. Shift
pressure to maximum, harsh gear shifts/
engagement.On On
P0753
(8, 26)* Shift solenoid (MV 1),
open or short circuitLimp home mode in low and high ranges. Shift
pressure to maximum, harsh gear shifts/
engagement.On On
P0758
(9, 27)* Shift solenoid (MV 2),
open or short circuitLimp home mode in low and high ranges. Shift
pressure to maximum, harsh gear shifts/
engagement.On On
P1562
(24)* Battery supply below
9V while engine
runningMaintains current gear in low range, limp
home mode in range. Shift pressure to
maximum, harsh gear shifts/engagement.Off On
P1601
(4)* ECU, EEPROM
checksumLimp home mode in low and high ranges. Shift
pressure to maximum, harsh gear shifts/
engagement.On On
P1606
(3)* EEPROM No apparent effect On†Off
P1606
(6)* Watchdog No apparent effect On On
P1612
(2)* Solenoid valves
power supply relay,
sticking closed or open
circuitLimp home mode in low and high ranges. Shift
pressure to maximum, harsh gear shifts/
engagement.On On

AUTOMATIC GEARBOX - ZF4HP22 - 24
ADJUSTMENTS 44-21
ADJUST ME NTS
Cable - selector
$% 44.30.04
Check
1.Position vehicle on ramp.
2.Select position 'P'.
3.Loosen selector cable trunnion nut.
4.Ensure that gearbox selector lever is in 'P'
position, (fully forward) and tighten trunnion
nut.
5.Lower ramp.
Stall test
$% 44.30.13
Testing
1.Chock the wheels and fully apply the
handbrake.
2.Start the engine and run it until it reaches
normal operating temperature.
3.Apply the footbrake and select 'D'.
4.Fully depress the accelerator pedal and note
the tachometer reading. The figures should be
as given below. Do not carry out stall test for
longer than 10 seconds, and DO NOT repeat
until 30 minutes have elapsed.
lV8: 2200 to 2400 rev/min
lDiesel: 2600 to 2800 rev/min
5.A reading below 1300 rev/min indicates a
torque converter fault, ie stator free-wheel.
6.A reading between 1300 and 2200 rev/min (V8)
or between 1300 and 2600 rev/min (Diesel)
indicates reduced engine power.
7.A reading above 2400 rev/min (V8) or above
2800 rev/min (Diesel) indicates clutch slip.
NOTE: The figures quoted above were
measured at sea level with an ambient
temperature of 20
°C (68°F). At higher altitudes
or higher ambient temperatures, these figures
will be reduced.

AUTOMATIC GEARBOX - ZF4HP22 - 24
44-38 REPAIRS
Housing - torque converter
$% 44.17.01
Remove
1.Remove torque converter oil seal.

+ AUTOMATIC GEARBOX - ZF4HP22
- 24, REPAIRS, Torque converter and oil
seal.
2.Remove 18 bolts and plain washers securing
torque converter and intermediate plate to
gearbox casing. Note the position of the 4 bolts
that have sealant applied to the bolt threads
and 6 bolts, (outer ring), which are shorter.
3.Hold input shaft in position and carefully
remove the converter housing and intermediate
plate from gearbox casing.
4.Note the position of the Torrington race on the
forward clutch hub and the thrust washer which
will stay attached to the intermediate plate by
fluid adhesion.
5.Remove and discard intermediate plate gasket.
6.Remove thrust washer from intermediate plate.
7.Separate converter housing from intermediate
plate.Refit
1.Clean converter housing, intermediate plate
and gearbox casing mating faces.
2.Clean bolts and plain washers and sealant from
4 bolt threads.
3.Apply Petroleum Jelly to new gasket and
position on gearbox casing.
4.Apply Petroleum Jelly to thrust washer and
Torrington race.
5.Correctly position Torrington race and thrust
washer to forward clutch hub.
6.Position intermediate plate and converter
housing to gearbox casing.
7.Apply sealant, Part No. STC 50553 to 4 longer
bolt threads and fit bolts in the positions shown.
8.Fit remaining bolts and tighten progressively in
a diagonal sequence to 46 Nm (34 lbf.ft).
9.Place LRT-44-003/1 into pump housing, tighten
screws to secure LRT-44-003/1 to input shaft.
10.Clamp a suitable steel base to converter
housing flange.
11.Mount DTI gauge and position gauge probe
onto LRT-44-003/1 and zero gauge.
M44 1343
M44 1345
M44 1343
M44 1358
LRT-44-003/1

AUTOMATIC GEARBOX - ZF4HP22 - 24
REPAIRS 44-39
12.Check that the axial end-float is between 0.2 to
0.4 mm. If end-float is not within limits, replace
existing thrust washer, positioned at rear of
intermediate plate, with a suitable thickness
thrust washer to give the required end-float.
13.Remove DTI gauge and base plate.
14.Fit torque converter oil seal.

+ AUTOMATIC GEARBOX - ZF4HP22
- 24, REPAIRS, Torque converter and oil
seal.
Gasket - intermediate plate
$% 44.20.11
Remove
1.Remove torque converter oil seal.

+ AUTOMATIC GEARBOX - ZF4HP22
- 24, REPAIRS, Torque converter and oil
seal.
2.Remove 12 bolts and plain washers securing
converter housing and intermediate plate to
gearbox casing. Note the position of the 4 bolts
that have sealant applied to the bolt threads.
3.Hold input shaft in position and carefully lift off
converter housing and intermediate plate as an
assembly. Note the position of the Torrington
race on the forward clutch hub, and the thrust
washer which will stay attached to the
intermediate plate by fluid adhesion.
4.Remove and discard intermediate plate gasket.
5.Remove thrust washer from intermediate plate.
M44 1344
M44 1345

AUTOMATIC GEARBOX - ZF4HP22 - 24
44-40 REPAIRS
Refit
1.Clean intermediate plate and mating face on
gearbox casing.
2.Apply Petroleum Jelly to new gasket and
position on gearbox casing.
3.Apply Petroleum Jelly to thrust washer and
Torrington race.
4.Correctly position Torrington race and thrust
washer to forward clutch hub.
5.Position converter housing and intermediate
plate assembly to gearbox casing.
6.Clean bolts and plain washers and old sealant
from 4 bolt threads.
7.Apply sealant, Part No. STC 50553 to 4 longer
bolt threads and fit bolts in position shown.
8.Fit remaining bolts and tighten progressively in
a diagonal sequence to 46 Nm (34 lbf.ft).
9.Place LRT-44-003/1 into pump housing, tighten
screws to secure LRT-44-003/1 to input shaft.
10.Clamp a suitable steel base to converter
housing flange.11.Mount DTI gauge and position gauge probe
onto LRT-44-003/1 and zero gauge.
12.Check that the axial end-float is between 0.2 to
0.4 mm (0.008 to 0.016 in). If end-float in not
within limits, replace existing thrust washer,
positioned at rear of intermediate plate, with a
suitable thickness thrust washer to give the
required end-float.
13.Remove DTI gauge and base plate.
14.Fit torque converter oil seal.

+ AUTOMATIC GEARBOX - ZF4HP22
- 24, REPAIRS, Torque converter and oil
seal.
M44 1344
M44 1358
LRT-44-003/1

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 70-21
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.

BRAKES
70-22 DESCRIPTION AND OPERATION
Minimum target speed
The minimum target speed depends on which gear is engaged. Reduced minimum target speeds are employed for
some gears if rough terrain or sharp bends are encountered while already travelling at the normal minimum target
speed. If loss of traction makes it impossible to maintain the minimum target speed, the SLABS ECU temporarily
increases the minimum target speed to maintain stability, then restores the normal minimum target speed when
traction improves.
HDC minimum target speeds
Fade out
To provide a safe transition from active braking to brakes off, the SLABS ECU invokes a fade out strategy if it detects
any of the following during active braking:
lA system fault.
lThe conditions for HDC are no longer being met.
lPossible brake overheat.
The fade out strategy increases the target speed at a low constant acceleration rate, independent of actual throttle
position. This results in the braking effort being gradually reduced and then discontinued. The SLABS ECU operates
warning indications during fade out that are dependent on the cause.
Fade out warning indications
Clutch disengagement/neutral selection
During active braking, if the SLABS ECU detects the clutch is disengaged or neutral is selected, it flashes the HDC
information warning lamp and sounds the audible warning continuously to indicate that conditions for HDC are no
longer being met. Initially, the SLABS ECU also fixes the target speed to the applicable minimum target speed, but if
the condition continues for approximately 60 seconds the SLABS ECU invokes fade out.
Brake overheat prevention
To prevent the brakes overheating, the SLABS ECU monitors the amount of active braking employed and, from this,
estimates brake temperature. If the SLABS ECU estimates the brake temperature has exceeded a preset limit, it
flashes the HDC fault warning lamp and sounds the audible warning continuously, to indicate that HDC should be
deselected to allow the brakes to cool. If active braking continues and the SLABS ECU estimates that brake
temperature has increased to an unacceptable level, fade out is employed and HDC is disabled. After fade out, the
audible warning is discontinued but the HDC fault warning lamp continues to flash, while HDC is selected, until the
SLABS ECU estimates brake temperature to be at an acceptable level. This calculation continues even if the ignition
is turned off, so turning the ignition off and back on will not reduce the disabled time. When the SLABS ECU estimates
the brake temperature to be acceptable, it extinguishes the HDC fault warning lamp and illuminates the HDC
information warning lamp to indicate that HDC is re-enabled. The disabled time is dependent on vehicle speed; typical
times at constant vehicle speeds are as follows:
Gear Speed, mph (km/h)
Manual gearbox Automatic gearbox
Normal Reduced Normal Reduced
1 4.4 (7.0) 4.4 (7.0) 4.4 (7.0) 4.4 (7.0)
2 5.2 (8.3) 4.4 (7.0) 4.4 (7.0) 4.4 (7.0)
3 6.0 (9.6) 4.4 (7.0) 7.5 (12.0) 6.0 (9.6)
4 7.5 (12.0) 6.0 (9.6) 7.5 (12.0) 6.0 (9.6)
5 8.8 (14.0) 7.0 (11.2) - -
Reverse 3.5 (5.6) 3.5 (5.6) 3.5 (5.6) 3.5 (5.6)
Neutral or clutch
disengaged8.8 (14.0) Last off road speed 4.4 (7.0) 4.4 (7.0)
Cause Warning indication
HDC fault warning lamp HDC information
warning lampAudible warning
Fault detected On Flashes Continuous
HDC conditions not met Off Flashes Continuous
Brake overheat prevention Flashes Off Continuous