Land Rover Discovery 99my To 03my Electrical Library 3rd Edition Rover Manual

							DESCRIPTION AND OPERATION
4.50DISCOVERY SERIES II
Ignition switch supply
With the ignition switch in position II, the feed from fusible link 8 flows through the ignition 
switch to the passenger compartment fusebox on a Y wire.
The feed continues through fuse 25 in the passenger compartment fusebox and is 
connected on a GO wire to the brake pedal switch.
Ignition and Shift Interlock Operation
Ignition interlock
A feed from fuse 20 in the passenger compartment fusebox is connected on a P wire to 
header C0289 LHD/C0294 RHD. From the the header the feed is connected on P wires to 
the key interlock unit. The feed is connected within the key interlock unit to the ignition switch 
illumination and the ignition key inserted switch.
When a door is opened or the vehicle is unlocked using the remote handset, the BCU 
provides an earth path for the ignition switch illumination. The earth path is from the interlock 
unit on a PU wire to pin C0663-9 on the BCU, via header C0285 LHD/C0294 RHD. The 
completed earth path allows the feed from fuse 20 in the passenger compartment fusebox 
to illuminate the bulb.
When the ignition key is inserted in the ignition switch, the ignition key inserted switch is 
tripped and allows the feed from fuse 20 in the passenger compartment fusebox to flow 
through the switch contacts. The feed is connected from the key interlock unit on a WP wire 
to pin C0662-2 on the BCU, via header C0293 LHD/C0289 RHD. This provides a signal to 
the BCU that the key is inserted.
A feed from fuse 21 in the passenger compartment fusebox is connected on a PB wire to 
the key interlock unit. The feed is connected within the interlock unit to the ignition key in 
position switch.
When the key is inserted in the ignition switch, the switch contacts close, allowing the feed 
from fuse 21 to pass on an OW wire to the interlock solenoid. If the transmission is in a 
position, other than PARK, the BCU will supply an earth path for the key interlock solenoid 
on a BLG wire. The solenoid will energise and removal of key from the ignition switch is 
prevented. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.51
Shift interlock
The shift interlock solenoid is normally in a de-energised state. When the transmission is to 
be moved from the PARK position, the ignition must be on and the brake pedal depressed. 
This energises the solenoid and allows movement of the transmission selector.
When the brake pedal is depressed, the feed from fuse 25 in the passenger compartment 
fusebox flows through the brake pedal switch contacts and is connected to BCU pin C0661-
7 on a GP wire via header C0287 LHD/C0290 RHD.
This feed signals the BCU that the ignition is on and the brake pedal is depressed. The BCU 
sends a signal, on an SK wire, via header C0293 LHD/C0292 RHD, to the IDM. The IDM in 
turn provides an earth path for the interlock relay in the passenger compartment fusebox, 
energising the relay coil and closing the relay contacts.
With the relay contacts closed, a feed from fuse 21 in the passenger compartment fusebox 
flows through the relay contacts and from the fusebox to the shift interlock solenoid on a LGP 
wire, energising the solenoid. The shift interlock solenoid is connected to earth header 
C0552 LHD/C0708 RHD on a B wire.
With the shift interlock solenoid energised, the transmission selector can be moved from the 
PARK position. When the brake pedal is released, the feed to the BCU is removed and the 
shift interlock solenoid is de-energised. The locking mechanism controlled by the solenoid 
will lock the transmission selector once it is returned to the park position.
Automatic transmission selector
A starter/ inhibitor/ reverse lights switch is located on the gearbox and is used to inform 
related components of the gear selector position. The connection used on this circuit is on 
an NP wire from the switch to pin C0663-10 on the BCU and signals the BCU of PARK and 
NEUTRAL selector positions.
Transmission neutral sensor
The transmission neutral sensor provides an earth signal to the BCU when the transfer box 
is in neutral. The earth signal causes the BCU to operate an audible warning to warn of the 
transfer box in neutral when the ignition is on.
The sensor is connected on a BK wire from pin C0662-15 on the BCU. The sensor is 
connected on a B wire, via header C1002 to earth header C0552. 
						

							DESCRIPTION AND OPERATION
4.52DISCOVERY SERIES II
Transfer gearbox interlock solenoid
When the BCU senses that the ignition key is removed from the ignition switch, it signals the 
IDM via the serial data bus. The IDM then grants an earth path for the coil of the transfer box 
relay in the passenger compartment fusebox, energising the relay coil and closing the relay 
contacts.
With the contacts closed, a feed from fuse 21 in the passenger compartment fusebox passes 
through the relay and is connected from the fusebox on an RU wire, via header C0293, to 
the transfer gearbox interlock solenoid. The solenoid energises and is connected by a B wire 
to earth header C0552. This prevents neutral being selected locking the transfer gearbox in 
high or low. A diode is located in the feed to the solenoid from splice joint A77 on an RU wire 
and from the diode to splice SJ2 on a B wire. The diode prevents residual current causing 
the solenoid to stick in the energised position. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.53
CRUISE CONTROL - V8 ENGINES
DESCRIPTION
General
The cruise control is selected from a switch located on the facia. The cruise control operation 
is governed by a cruise control ECU located on the RH A post behind the trim panel. 
Operation is controlled from two switches located on the steering wheel, a set/accelerate 
switch (SET+) and a resume/suspend switch (RES.).
A speed signal is supplied from the SLABS ECU to the cruise control ECU, the cruise control 
ECU monitors the signal for use in its control logic circuits. The cruise control system ECU 
supplies outputs to operate a vacuum pump and its internal control/dump valves.
The vacuum acting within a pneumatic throttle actuator moves the actuator to the required 
position.
Cruise suspend/resume - manual gearbox
Inputs to the cruise control ECU from a switch on the brake pedal mechanism or the clutch 
pedal mechanism can disengage the cruise control by interrupting a feed into the cruise 
control ECU. The feed is used by the ECU to power the cruise control pump. When the feed 
is interrupted the ECU logic circuits stop the operation of the cruise control pump, open an 
internal dump valve, and close an internal control valve. This action stops the actuator and 
suspends the cruise control function.
In addition to the feed removal to the ECU when the brake pedal is pressed, a low voltage 
brakelight signal is also sent via the Body Control Unit (BCU) to the cruise control ECU. The 
brakelight signal is also used by the logic circuits in the cruise control ECU, to control the 
operation of the throttle actuator and control valves when the brake pedal has been pressed.
Operation of the resume/suspend switch after a braking event, can restore the operation of 
the cruise control system if the vehicles speed is acceptable to the cruise control ECU.
Cruise suspend/resume - automatic gearbox
A gearbox selector lever position sensor sends an input via the BCU to the cruise control 
ECU if the selector lever is in park, neutral or reverse. An input to the cruise control ECU 
from a switch on the brake pedal mechanism will also disengage the cruise control by 
interrupting a feed to the cruise control ECU. The feed is used by the ECU to power the 
cruise control pump. When the feed is interrupted the ECU logic circuits stop the operation 
of the cruise control pump, open an internal dump valve, and close an internal control valve. 
This action stops the throttle actuator and suspends the cruise control function. 
						

							DESCRIPTION AND OPERATION
4.54DISCOVERY SERIES II
In addition to the feed removal to the ECU when the brake pedal is pressed, a low voltage 
brakelight signal is also sent via the BCU to the cruise control ECU. The brakelight signal 
is also used by the logic circuits in the cruise control ECU, to control the operation of the 
throttle actuator and control/dump valves when the brake pedal has been pressed.
Operation of the resume/suspend switch after a braking event, can restore the operation of 
the cruise control system if the vehicles speed and gearbox selector position is acceptable 
to the cruise control ECU.
OPERATION
Cruise Control Supply
Circuit supply
A feed from the battery positive terminal is connected by a R wire to the engine compartment 
fusebox, where it passes through fuse 16 and fusible link 8.
A feed from fuse 16 passes to the coil of the horn relay. From the coil of the horn relay, the 
feed is connected to the set/accel and res/suspend switches on a PO wire, via header 
C0291 LHD/C0286 RHD and the rotary coupler.
A feed from fusible link 8 is connected to the passenger compartment fusebox on a NW wire 
and from the fusebox to the ignition switch on a N wire.
Ignition switch supply
With the ignition switch in position II, the feed from fusible link 8 flows from the ignition switch 
to the passenger compartment fusebox on a W wire. The feed continues through fuse 30 in 
the passenger compartment fusebox and is connected by a GLG wire to the cruise control 
switch.
With the ignition switch in position II, a second feed from fusible link 8 flows from the ignition 
switch to the passenger compartment fusebox on a Y wire. The feed continues through fuse 
25 in the passenger compartment fusebox and is connected to the brake pedal switch by a 
GO wire. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.55
Cruise Control Operation
When the cruise control switch is on, the feed from fuse 30 in the passenger compartment 
fusebox, passes through the cruise control switch contacts to provide power input to the 
cruise control ECU pin C0239-8 on a WY wire.
Simultaneously, the feed also passes through the cruise control switch indicator lamp which 
illuminates. The indicator lamp is connected to earth on a black wire via header C0760 to 
earth header C0017 LHD/C0018 RHD. The cruise control ECU is earthed on a B wire from 
pin C0239-18, via header C0286 LHD/C0291 RHD to earth header C0018 LHD/C0017 
RHD.
When the brake or clutch pedal or is not depressed, the feed from fuse 25 in the passenger 
compartment fusebox flows to a pair of contacts in the brake pedal switch on a GO wire.
Manual transmission
The feed passes from the contacts of the brake pedal switch and is connected to the clutch 
pedal switch by an OG wire. The feed passes through the closed contacts of the clutch pedal 
switch to a PG wire that is connected to pin C0239-1 on the cruise control ECU. This feed 
provides the power source to the cruise control pump via the cruise control ECU.
If either the clutch pedal or the brake pedal is depressed, the respective switch contacts will 
be opened, removing power from the cruise control ECU and disengaging cruise control. If 
the cruise control switch remains on, the previous speed will be retained in the cruise control 
ECU memory.
The previous speed can be resumed by operation of the resume/suspend switch. The cruise 
control ECU will engage the cruise control if:
zThe vehicle is travelling at over 28 mph (45 km/h)
zThe cruise control switch is still on and has not been turned off
zThe brake pedal is not depressed.
zThe clutch pedal is not depressed.
Automatic transmission
The feed from the contacts of the brake pedal switch is connected by an OG wire to 
connector interface C0712-2/C0667-1. From the connector interface the feed continues on 
a PG wire to the cruise control ECU. The feed from the brake pedal switch provides the 
power source to the cruise control pump via the cruise control ECU.
The cruise control ECU will engage the cruise control if:
zThe vehicle is travelling at over 28 mph (45 km/h)
zThe gearbox selector position is acceptable to the cruise control ECU
zThe cruise control switch is still on and has not been turned off
zThe brake pedal is not depressed. 
						

							DESCRIPTION AND OPERATION
4.56DISCOVERY SERIES II
Speed signal
The cruise control ECU receives a speed signal input on a KG wire via header C0290 to pin 
C0239-15, from pin C0504-3 on the SLABS ECU.
Cruise set/accelerate
When the set/accel switch is operated, the switch contacts close and connect the feed from 
the horn relay to cruise control ECU pin C0239-4, via the rotary coupler and an RW wire. 
This signal initiates the cruise control ECU to activate the cruise control pump functions, 
providing all other parameters are correct.
Cruise resume/suspend
When the res/suspend switch is operated, the switch contacts close and connect the feed 
from the horn relay to cruise control ECU pin C0239-2, via the rotary coupler and a UW wire. 
If cruise control is engaged, this signal suspends cruise control operation. If cruise control is 
suspended, the signal will initiate the cruise control ECU to engage cruise control at the 
speed retained in the ECUs memory.
Cruise control pump
The cruise control pump has three connections to the cruise control ECU. One connection 
on a WU wire from pin C0239-11 supplies power directly to the pump. The control valve 
solenoid and dump valve solenoid are connected to pin C0239-17 of the cruise control ECU 
on a BY wire. The pump is earthed via pin C0239-7 of the cruise control ECU on a BR wire.
The dump valve solenoid is connected via header C0287 LHD/C0290 RHD on a GP wire to 
the contacts of the brake pedal switch. In normal operation the coil of the dump valve is 
earthed by the brake light circuit, via the contacts of the the brake pedal switch. When the 
brake pedal is pressed power is supplied on the earth path of the dump valve solenoid. 
When the voltage on each side of the coil of the dump valve solenoid is equalised, there is 
no voltage drop across the solenoid. With no current flowing through the coil of the dump 
valve solenoid, the solenoid is de-energised and the dump valve opens.
When the cruise control switch is on and vehicle speed is more than 28 mph (45km/h) and 
less than 125 mph (201 km/h), the cruise control ECU supplies power to the pump and valve 
solenoids. The earth paths for the pump and the control valve solenoid are switched as 
required by the cruise control ECU to set and maintain vehicle speed. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.57
Other Body Control Unit (BCU) inputs/outputs
Brakelight Signal
If the brake pedal is depressed a pair of contacts in the brake pedal switch allow a feed to 
flow on a GP wire via header C0287 LHD/C0290 RHD to pin C0661-7 on the BCU. The BCU 
sends a brakelight signal output from pin C0661-16 on a GS wire, to pin C0239-5 on the 
cruise control ECU.
The logic circuits in the cruise control ECU use this brakelight signal to lock out the cruise 
control. The internal logic of the ECU uses the brakelight signal to cancel cruise control by 
interrupting the earth path to the pump, and activating the dump valve solenoid. The dump 
valve opens the vacuum chamber to ambient air pressure, the vacuum is dissipated and the 
throttle actuator no longer has an effect on the throttle position.
Gearbox inputs - automatic transmission
An Input for Park, Neutral and Reverse positions are passed from the gearbox position 
selector on a BG wire via splice joint A31 and connectors C0668-5, C0681-5 to pin C0663-
11 of the BCU.
If an input from the gearbox position selector or the brake pedal switch is received by the 
BCU, a brakelight signal is sent from the BCU to the cruise control ECU, This signal will 
cancel or inhibit cruise control operation.
Gearbox inputs - manual transmission
There are no signals from the manual gearbox to the BCU. The BCU is permanently 
connected to earth header C0552, via a BG wire from pin C0663-11 through connectors 
C0668-5 and C0661-5 to splice joint A33. From splice joint A33 the earth continues on a B 
wire through connectors C0681-8 and C0668-8 to earth header C0552.
Diagnostic socket - all models
Diagnostic information can be retrieved on a K wire from cruise control ECU pin C0239-16, 
through header C0286, to the diagnostic socket. The information can be retrieved using 
TestBook/T4 or other suitable scantool. 
						

							DESCRIPTION AND OPERATION
4.58DISCOVERY SERIES II
CRUISE CONTROL - Td5 ENGINES
DESCRIPTION
General
Cruise control is integral with the engine management system. Refer to Workshop Manual - 
Engine Management System Td5 - Diesel for description and operation. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.59
ELECTRONIC AUTOMATIC TRANSMISSION (EAT)
DESCRIPTION
General
The automatic gearbox is a four speed unit with electronic control of gear selection, shift 
quality and torque converter lock-up. A starter/ inhibitor/ reverse light switch on the gearbox 
transmits gear selector position to the EAT ECU, which outputs appropriate signals to an 
electro-hydraulic valve block in the gearbox. The signals from the starter/ inhibitor/ reverse 
light switch are also transmitted to the BCU, which uses them to operate the gear selected 
indicator in the instrument pack.
The EAT ECU is located under the LH front seat below the radio/cassette player power 
amplifier (if fitted). A mode switch on the gear selector panel allows the driver to change the 
mode of the ECU operation between manual and sport modes. Warning lamps in the 
instrument pack are operated by the ECU to indicate control mode and system status.
Refer to Workshop Manual Automatic Gearbox for Description and Operation of the EAT.
OPERATION
EAT Supply
Circuit supply
A feed from the battery positive terminal is connected on an R wire to the engine 
compartment fusebox where it passes through fusible link 8 and fuse 12.
The feed from fuse 12 is connected from the fusebox on a PY wire to the EAT ECU pin 
C0193-26 and supplies a continuous battery feed to the ECU.
The feed from fusible link 8 is connected on an NW wire to the passenger compartment 
fusebox and from the fusebox to the ignition switch on an N wire.
Ignition switch supply
With the ignition switch in position II, the feed from fusible link 8 passes through the ignition 
switch to the passenger compartment fusebox on a Y wire, where it passes through fuses 
24 and 25.
The feed from fuse 24 is connected from the fusebox to the EAT ECU pin C0193-54 on an 
LGO wire to inform the ECU that the ignition is on. The feed from fuse 25 is connected from 
the fusebox to the starter/ inhibitor/ reverse light switch pin C0675-2 on a GY wire.