AUTOMATIC GEARBOX
B7
CIRCUIT OPERATION
2
REV: 11/2000
Output Shaft Speed Sensor – pins 2, 38, 20
Diesel (pins 42, 14, 15 Petrol)
The automatic gearbox system incorporates an
output shaft speed sensor which provides an input to
the Auto Gearbox Control Unit (Z255) on pin 2 diesel
(pin 42 petrol) and pin 38 diesel (pin14 petrol) with a
screen over the cable attached to pin 20 diesel (pin
15 petrol). It is important that this signal is screened
correctly.
MES 1 and 2 – pins 16, 31 Diesel (pins 25, 51
Petrol)
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 occurred.
Interface to Transmission Gearbox Control Unit
(Z256)
High/Low Range Signal – pin 46 Diesel (pin 13
Petrol)
The High/Low signal is used by the Auto Gearbox
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 Diesel (pin 45
Petrol)
The H–Gate sensor module (Z254) displays selected
gear information from the Gearbox Position Switch
(X294), ratio information from the Transmission
Gearbox Control Unit (Z256) and mode information
from Auto Gearbox Control Unit (Z255). The H–Gate
receives a signal from the ignition switch when it is
turned to position II on a W wire. This is supplied via
fuse 6 and is grounded to the console ground E0808
via a B wire.
Information on the selected gear is received from the
Gearbox Position Switch (X294) on UB, UP and UG
wires. These three lines also provide a feed to the
Auto Gearbox Control Unit (Z255) and the BeCM
(Z238).
Information on the gearbox mode (sport or manual)
is received on a YG wire and a YR wire. These two
lines also go to the BeCM (Z238).
The Transmission Gearbox Control Unit (Z256) high
status is received on a 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 a RU wire.
The mode request is on the UO wire. This is sent
from the H–gate Sensor Module (Z254) to the Auto
Gearbox Control Unit (Z255). The line is activated
and deactivated by pressing the momentary action
MODE button. The line is active at all times.
Gearbox Oil Cooler – Diesel
The gearbox cooling process relies mainly on ram air
entering through an aperture in the LH side of the
bumper moulding and is dispersed over the oil
cooler. The cooled oil is fed back to the automatic
gearbox via the return pipe, which is located parallel
to the feed pipe on the LH side on the automatic
gearbox.
A small electric fan is fitted to the front of the oil
cooler to cool the gearbox oil during long periods of
elevated gearbox oil temperatures i.e. during
extended idle in drive or low speed towing. A
gearbox oil temperature switch is fitted adjacent to
the warning light switch on the oil cooler. This switch
monitors the gearbox oil temperature. When the
gearbox oil temperature reaches 95
_
C
±
3
_
C the
switch provides the ground for the oil cooler relay
located in the engine compartment fusebox.
The relay receives a power supply on pin 86 from
shorting link 8 (J792) in the engine compartment
fusebox. The ground for the relay pin 85 is provided
through the gearbox oil temperature switch. The
relay therefore will not energise unless the gearbox
oil temperature switch reaches its defined limit of
95
_
C
±
3
_
C.
A separate power supply is connected to the relay
pin 30 from fuse F28 (30A). When the gearbox oil
temperature switch energises the relay, power is
routed via relay pin 87 to the electric fan located on
the front of the oil cooler.
As gearbox oil temperature decreases the oil
temperature switch deactivates the relay by breaking
the relay coil ground circuit. As the ground circuit for
the relay is interrupted, the power supply is
disconnected.
The ground for both the gearbox oil temperature
switch and the electric fan is via a ground point
(E0557).