Range Rover 2. Electrical Manual

TRANSFER GEARBOX

CIRCUIT DIAGRAM

C626

C603

E529

S551

See Ground Dis-
tribution

C660

C560

C563

E574

Petrol

Diesel

Z238
Body Electrical
Control Module
(BECM)

X293
Neutral Switch

Z256
Transfer Gear
Box ECU

Manual Trans-
mission

TRANSFER GEARBOX

CIRCUIT DIAGRAM

Z256
Transfer Gear
Box ECU

K154
Transfer Box
Drive Motor/
Encoder

C660

C560

C568

C658

C603

C568

C558

S2 S3 S4

C603

Z256
Transfer Gear
Box ECU

C560

C660

Left Stop

Left of Hi Mode

Neutral Mode

Zone 1

Right of Hi Mode

Hi Mode

Right Stop

Lo Mode

Zone 2

1 =

0 =

Switch Open

Switch Closed

AUTOMATIC GEARBOX

CIRCUIT OPERATION

CIRCUIT OPERATION

Economy, Sport and Manual Modes

The Auto Gear Box 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 the gear change much more
sensitive to throttle movement, thereby shifting down
earlier and holding onto lower gears longer than the
Economy mode equivalent. If the vehicle is in Low
range, then Manual mode can be selected. This will
make the gear box change into the selected gear as
quickly as possible and hold on to that gear at all
speeds, i.e. if “3” is selected, then the gear box will
not shift down to “2” or “1” as the vehicle slows
down. It will only change gear to prevent the vehicle
from stalling.

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

The Auto Gear Box Control Unit (Z255) takes the
engine torque, engine speed and throttle angle
signals from the ECM, calculates which gear is
required, outputs to the solenoid valves and sends a
torque reduction signal back to the ECM, thereby
retarding the ignition point on each of the cylinders
and so giving a reduction in engine power during
gear changes that result in a smooth change.

The engine torque is received by the Auto Gear Box
Control Unit (Z255) on its pin 21, the engine speed
on pin 3 and the throttle angle on pin 47. The torque
reduction signal is sent to the ECM from the Auto
Gear Box Control Unit (Z255) via its pin 32.

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

The functionality of the interface is similar to the
petrol interface, except for the format of the signal.

Interface to Auto Gear Box Control Unit (Z255)

Gear position Switch– pins 14, 33, 50

The gear position switch is mounted on the side of
the gearbox and contains five internal switches,
although only 3 are connected to the Auto Gear Box
Control Unit (Z255)via pins 50, 14, and 33. By
analysing the status of these 3 switches, the Auto
Gear Box Control Unit (Z255) calculates which gear
the vehicle is in.

If a fault occurs with the switch, then the Auto Gear
Box Control Unit (Z255) may try to put the gearbox
into a different gear than the driver’s request.

Solenoid Valves– pins 5, 6, 19, 24, 42

The Auto Gear Box 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, which is activated via a relay in
the Auto Gear Box Control Unit (Z255) itself.

MV1 – pin 5, MV2 – pin 24:

When the driver selects “D”rive, then the Auto Gear
Box Control Unit (Z255) controls the gear selection
by the use of the two solenoid valves. If a fault
occurs with one or both of the valves, then a
different gear than the one selected will result.

If the Auto Gear Box Control Unit (Z255) defaults the
gearbox, then 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.

AUTOMATIC GEARBOX

CIRCUIT OPERATION

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

Torque Converter Lock–Up Solenoid – pin 42:

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

Pressure Regulator Solenoid – pin 6:

The gear shift quality is controlled by modulating the
pressure regulator, which is controlled by the Auto
Gear Box Control Unit (Z255). The solenoid is
energised closed, such that if a failure occurs, then
the regulator allows default gear change.

Output Shaft Speed Sensor – pins 2, 38, 20

The automatic gearbox system incorporates an
output shaft speed sensor which is input to the Auto
Gear Box Control Unit (Z255) on pins 2 and 38 with
a screen over the cable attached to pin 20. It is
important that this signal is screened correctly.

MES 1 and 2– pins 16, 31

The two Manual/Economy/Sport (MES) lines indicate
to the BeCM (Z238) which mode has been selected
or if a fault within the transmission has occured.

Interface to Transmission Gearbox Control Unit
(Z256)

– High/Low Range Signal– pin 46

The High/Low signal is used by the Auto Gear Box
Control Unit (Z255) to select the correct mode on
application of the “MES” switch. Also, the gear shift
points and strategies are very different in the
different ranges.

Interface to “H–Gate”– pin 29

The “H”–Gate sensor module (Z254) displays
selected gear information from the Gear Box
Position Switch (X294), ratio information from the
Transmission Gearbox Control Unit (Z256) and
mode information from the gear box Auto Gear Box
Control Unit (Z255). The H–Gate receives an ignition
2 signal on the W wire. This is fed via fuse 6. It is
grounded to the console ground E621 via the B wire.

Information on the selected gear (PRNDL) is
received from the Gear Box Position Switch (X294)
on wires UB, UP, UG. These three lines also go to

the Auto Gear Box Control Unit (Z255) and the
BeCM (Z238).

Information on the gear box mode (sport or manual)
is received on the YG wire and the YR wire. These
two lines also go to the BeCM (Z238).

The Transmission Gearbox Control Unit (Z256) high
status is received on the NY wire. The low status is
received on the NR wire. These two lines also go the
Transmission Gearbox Control Unit (Z256) and the
BeCM (Z238).

The illumination signal is on the RU wire.

The mode request is on the UO wire. This is sent
from the H–gate Sensor Module (Z254) to the Auto
Gear Box Control Unit (Z255). The line is activated
and deactivated by pressing the momentary action
MODE button. The line is active at all times.

Range Rover 2. Electrical Manual - part 23