Discovery 2. Manual — part 570

AUTOMATIC GEARBOX - ZF4HP22 - 24

DESCRIPTION AND OPERATION

44-19

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.

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 outputs

Maintains 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
overspeed

Maintains 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
slipping

Maintains 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 ratio

No apparent effect

On

On

P0732

(30)

* Ratio monitoring,
implausible 2nd gear
ratio

No apparent effect

On

Off

P0733

(31)

* Ratio monitoring,
implausible 3rd gear
ratio

No apparent effect

On

Off

P0734

(32)

* Ratio monitoring,
implausible 4th gear ratio

No apparent effect

On

Off

P0741

(5)

* Torque converter lock-
up clutch fault

May affect driveability.

On

Off

P0743
(7, 25)

* Torque converter lock-
up solenoid (MV 3), open
or short circuit

Limp 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 circuit

Limp 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 circuit

Limp 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 circuit

Limp 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 running

Maintains current gear in low range, limp home
mode in range. Shift pressure to maximum, harsh
gear shifts/engagement.

Off

On

AUTOMATIC GEARBOX - ZF4HP22 - 24

44-20

DESCRIPTION AND OPERATION

P1601

(4)

* ECU, EEPROM
checksum

Limp 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 circuit

Limp home mode in low and high ranges. Shift
pressure to maximum, harsh gear shifts/
engagement.

On

On

P1613

(1)

* Solenoid valves power
supply relay, sticking
open or short circuit

Limp home mode in low and high ranges. Shift
pressure to maximum, harsh gear shifts/
engagement.

On

On

P1705

(39)

Transmission high/low
range, implausible input

No apparent effect

On

Off

P1810

(12, 13)

Sport/Manual warning
lamp circuit fault

Lamp fails bulb check or is permanently
illuminated. No effect on gearbox operation.

On

Off

P1841

(16)

* CAN bus fault

Maintains current gear in low range, limp home
mode in high range. Shift pressure to maximum,
harsh gear shifts/engagement.

On

On

P1842

(15)

* CAN level monitoring

Maintains current gear in low range, limp home
mode in range. Shift pressure to maximum, harsh
gear shifts/engagement.

On

On

P1843

(17)

* CAN time-out
monitoring

Maintains current gear in low range, limp home
mode in high range. Shift pressure to maximum,
harsh gear shifts/engagement.

On

On

P1884
(11)

* CAN message: Engine
friction invalid

No apparent effect.

On

Off

P1884
(18)

* CAN message: Throttle
position invalid

Substitute throttle angle of 50% adopted. No
kickdown. Operates in economy modes only.

On

On

P1884
(19)

CAN message: Engine
temperature invalid

Substitute engine temperature derived from other
inputs. No apparent effect.

On

Off

P1884
(20)

CAN message: Road
speed invalid

No apparent effect

On

Off

P1884
(33, 34)

* CAN message: Engine
torque invalid

Substitute engine torque of derived from other
inputs. May affect shift quality.

On

Off

P1884
(35)

* CAN message: Engine
speed invalid

Maintains current gear in low range, limp home
mode in high range. Shift pressure to maximum,
harsh gear shifts/engagement.

On

On

P1884
(37)

CAN message: Engine
air intake temperature
invalid

No apparent effect.

On

Off

P1844

(38)

Altitude shift control
invalid

No reduced torque compensation, possible
reduction in performance/ driveability at altitude
or high ambient temperatures.

On

Off

* = Emissions (OBD II) relevant
†On = MIL illuminates immediately (in all other faults, MIL On = illuminates in the 2nd consecutive drive cycle if fault still
present)

Fault code,

OBD II

(TestBook)

Fault description

Effect

Warning lamp

illumination

MIL

Sport/

Manual

AUTOMATIC GEARBOX - ZF4HP22 - 24

ADJUSTMENTS

44-21

ADJUSTMENTS

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.

l

V8: 2200 to 2400 rev/min

l

Diesel: 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

44-22

ADJUSTMENTS