Range Rover 2. Electrical Manual - part 168

TRANSFER GEARBOX

B6

6

CIRCUIT DIAGRAM

Diesel

20

Automatic
Transmission

28

C0411

UN

UN

C0448

13

34

C1319

C0868

3

C0903

8

UB

1

X294
Gear Box
Position Switch

[1]

X Switch

[2]

Y Switch

[3]

Z Switch

[1]

0

9

UP

2

See Ground
Distribution

6

E0808

C0244

[2]

0

5

C0745

4

3

18

C1287

UG

3

[3]

0

C0244

S608

S609

S610

Automatic
Gearbox

C0988

X

Y

Z

C1287

Z256
Transfer Gear
Box ECU

Z132
Engine Control
Module (ECM)

Z238
Body Electrical
Control Module
(BECM)

Petrol

8

C0637

UN

C0162

13

C0448

28

C1319

C0868

3

C0903

Z132
Engine Control
Module (ECM)

P

0

1

1

R

0

0

1

N

1

0

1

D

1

0

0

3

0

0

0

2

0

1

0

1

1

1

0

Z*

1

1

1

X

Y

Z

1 =

0 =

* =

Switch Open

Switch Closed

Fault

C0203

TRANSFER GEARBOX

B6

7

CIRCUIT DIAGRAM

18

C1287

1

N

2

0

1

34

C1319

E1355

S551

N

B

See Ground
Distribution

C0746

14

C0989

C0684

C0684

Z238
Body Electrical
Control Module
(BECM)

X293
Neutral Switch

Z256
Transfer Gear
Box ECU

Manual
Transmission

TRANSFER GEARBOX

B6

8

CIRCUIT DIAGRAM

5

Z256
Transfer Gear
Box ECU

17

KB

1

K154
Transfer Box
Solenoid

1

0

32

KN

2

1

0

4

2

1

7

KR

4

1

0

S1

S2

S4

31

KU

3

1

0

S3

3

C0683

25

RP

26

RP

7

11

C0746

12

1

C1319

RS

8

C0683

C0989

2

1

1

1

0

1

0

0

1

0

0

1

0

0

0

0

0

1

0

0

0

1

0

0

1

0

0

1

0

0

1

0

1

S2 S3 S4

19

C1319

Z256
Transfer Gear
Box ECU

BG

C0989

5

C0746

BG

M

S1

Left Stop

Left of Hi Mode

Neutral Mode

Zone 1

Right of Hi Mode

Hi Mode

Right Stop

Lo Mode

Zone 2

RS

0

1

0

0

1 =

0 =

Switch Open

Switch Closed

S614

S613

AUTOMATIC GEARBOX

B7

CIRCUIT OPERATION

1

REV: 11/2000

CIRCUIT OPERATION

Economy, Sport and Manual Modes

The Auto Gearbox Control Unit (Z255) has various
different driving modes available, with Economy
being selected automatically on start up. When the
vehicle is in High range, Sport mode can be
selected. This will make gear changes more
sensitive to throttle movement, thereby shifting down
earlier and holding lower gears longer than the
Economy mode. If the vehicle is in Low range,
Manual mode can be selected. This will make the
gearbox change into the selected gear as quickly as
possible and hold on to that gear at all speeds.

Interface to Petrol Engine Control Module (ECM)
(Z132)

The Auto Gearbox Control Unit (Z255) uses engine
torque, engine speed and throttle angle signals from
the ECM (Z132) to calculate which gear is required.
The Auto Box Control Unit supplies gear selection
information to the solenoid valves which will then
engage the correct gear. 
A torque reduction signal is sent from the Auto
Gearbox Control Unit to the ECM which will retard
the ignition point on each cylinder. This reduces
engine power during gear changes. The combination
of retarded ignition and reduced engine power
delivers a smoother gear change.

Information about engine speed, engine torque,
throttle angle and torque reduction is received from
the ECM (Z132) by the Auto Gear Box Control Unit
(Z255) via CAN bus ‘high’ and ‘low’ line on pins 16
and 44.

Interface to Diesel Engine Control Module (ECM)
(Z132)

Engine speed is received by the Auto Gearbox
Control Unit (Z255) on pin 3, the throttle angle on 
pin 47. 
The torque reduction signal is sent to the ECM from
the Auto Gearbox Control Unit (Z255) via pin 32.

Interface to Auto Gear Box Control Unit (Z255) 
Gear Box Position Switch – pins 14, 33, 50, 
Diesel (pins 8, 36, 37 Petrol)

The Gearbox Position Switch (X294) is mounted on
the side of the gearbox and contains 3 internal
switches. The switches are connected to the Auto

Gearbox Control Unit (Z255) via pins 50, 14 and 33
for diesel (pins 8, 36, 37 for petrol). By analysing the
status of these 3 switches, the Auto Gearbox Control
Unit (Z255) calculates which gear the vehicle is in.

If a fault occurs with the switch, the Auto Gearbox
Control Unit (Z255) may try to override driver
requests and select a different gear.

Solenoid Valves –  pins 5, 6, 19, 24, 42 
Diesel (pins 5, 30, 32, 33, 53 Petrol)

The Auto Gearbox Control Unit (Z255) has control
over 4 solenoid valves: MV1, MV2, torque converter
lock up and pressure regulator. These are all
supplied via pin 19 diesel (pin 53 petrol), which is
activated via a relay in the Auto Gearbox Control
Unit (Z255) itself.

MV1 – pin 5 Diesel (pin 30 Petrol), 
MV2 – pin 24 Diesel (pin 33 Petrol)

When the driver selects ”D” (drive), the Auto
Gearbox Control Unit (Z255) controls gear selection
via two solenoid valves. If a fault occurs with one or
both of the valves, a different gear than the one
selected will result.

If the Auto Gear Box Control Unit (Z255) defaults the
gearbox, the common supply to all the solenoid
valves is removed and the gearbox mechanically
shifts either to third gear, if the vehicle is stationary,
or fourth, if moving.

MV2 is also used to prevent the driver from selecting
reverse gear when the vehicle is moving forward at
speeds greater than 8 km/h and from disengaging
reverse gear at speeds greater than 6 km/h. 
This function is known as ”Reverse Safety” and will
not be available if MV2 is non–operational and/or the
gearbox is in default mode.

Torque Converter Lock–Up Solenoid – 
pin 42 Diesel (pin 32 Petrol)

The torque converter slips to allow smooth operation
of the gearbox. Lock–Up occurs when the vehicle
reaches a speed of 45 mph or above in either third
or fourth gears.

Pressure Regulator Solenoid – pin 6 Diesel 
(pin 5 Petrol)

Gearshift quality is controlled by modulating the
pressure regulator which is controlled by the Auto
Gearbox Control Unit (Z255). When energised the
solenoid is in the closed position. If a failure occurs,
then the regulator only allows mechanical gear
change between third and fourth gears.