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

							DESCRIPTION AND OPERATION
4.90DISCOVERY SERIES II
OPERATION
Cooling Fan Supply
Circuit supply
A permanent feed from the battery positive terminal is connected by an R wire to the engine 
compartment fusebox. A feed from this wire is connected to the contacts of the main relay 
and also to fuse 13. The feed passes through fuse 13 and to the inertia switch on a NB wire. 
The feed from the inertia switch flows on a WG wire to the engine compartment fusebox and 
is connected to the coils of the main relay. in this condition the coil and contacts of the main 
relay receive a permanent supply.
The permanent feed from the battery on a R wire to the engine compartment fusebox is also 
connected via fusible link 1 to fuse 5. From fuse 5 the permanent feed is connected to the 
contacts on the cooling fan relay. In this condition the contacts of the fan relay receives a 
permanent feed from the battery via fuse 5.
Main relay - ignition supply
When the ignition switch is a position II, the ECM switches on the earth path for coil of the 
main relay. Current flows through the coil of the main relay and flows on a UR wire to pin 
C0635-23 V8/C0658-21 Td5 on the ECM. With the coil of the main relay energised the main 
relay contacts close, power is now available to the coil of the cooling fan relay, via the closed 
contacts of the main relay.
Cooling Fan Operation
V8 engine
The engine coolant temperature sensor sends an input on a G wire to pin C0636-22 on the 
ECM. The engine coolant temperature sensor is earthed on a RB wire to pin C0636-21 on 
the ECM.
When the coolant temperature is high, the value of input from the coolant temperature 
sensor causes the ECM logic to switch on the earth path for the coil of the cooling relay, on 
a GW wire to pin C0636-31 on the ECM. With the coil of the cooling relay earthed the coil is 
now energised. The cooling relay contacts close and current flows on a BN wire to the 
cooling fan motor. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.91
Td5 engine
The engine coolant temperature sensor sends an input on a KG wire to pin C0158-7 on the 
ECM. The engine coolant temperature sensor is earthed on a KB wire to pin C0158-18 on 
the ECM.
When the coolant temperature is high, the value of input from the coolant temperature 
sensor causes the ECM logic to switch on the earth path for the coil of the cooling relay, on 
a BP wire to pin C0658-4 on the ECM. With the coil of the cooling relay earthed the coil is 
now energised. The cooling relay contacts close and current flows on a BN wire to the 
cooling fan motor.
All models
The current flows through the cooling fan motor to earth header C0018 on a B wire. The 
cooling fan motor will operate as long as the ECM receives a high signal input from the 
coolant temperature sensor. When the coolant temperature is low, the ECM logic interrupts 
the earth path to the coil of the cooling relay. The contacts of the cooling fan relay open, the 
fan motor power supply is now broken and the motor stops. The cooling fan will cycle on and 
off as the coolant temperature rises and falls. 
						

							DESCRIPTION AND OPERATION
4.92DISCOVERY SERIES II
HEATED REAR WINDOW (HRW)
DESCRIPTION
General
The HRW is operated from a non-latching switch located to the left of the instrument pack. 
The switch has an indicator light to show when the HRW is operating. The HRW element 
comprises fourteen metallic strips bonded to the inside surface of the rear window. The 
HRW will only function when the engine is running due to the high current draw and 
subsequent load on the battery.
The HRW can also be operated by the air temperature control ECU on vehicles fitted with 
air conditioning.
When the HRW is selected on, heater elements in the door mirror glass also operate. Refer 
to Mirrors - Description and Operation in this manual for details.
OPERATION
Heated Rear Window Supply
Circuit supply
A feed from the battery positive terminal is connected by an R wire to the engine 
compartment fusebox, where it passes through fusible links 1, 6, 8 and fuse 13. Fusible links 
1 and 6 are connected in series.
A feed from fusible links 1 and 6 is connected from the engine compartment fusebox to the 
passenger compartment fusebox on an S wire, where it passes through fuse 8 and is 
connected to the contacts of the heated rear screen relay.
A feed from fuse 13 in the engine compartment fusebox is connected on a PN wire to the 
Body Control Unit (BCU).
A second feed from fuse 13 is connected on a PN wire to the passenger compartment 
fusebox and is connected to the coil of the heated rear screen relay.
A feed from fusible link 8 in the engine compartment fusebox 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
When the ignition switch is 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 
29 in the passenger compartment fusebox and is connected to the BCU on a GU wire. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.93
Heated Rear Window Switch Operation
When the HRW switch is operated, an earth path is completed from the HRW switch to earth 
header C0017 LHD/C0018 RHD on a B wire, via header C0760.
The completion of the earth path from the HRW switch, completes an earth path from the 
BCU to the switch on an NB wire. The earth path completes a circuit within the BCU for an 
internal electronic switch which receives its feed from fuse 29 in the passenger compartment 
fusebox.
The internal switch closes, completing a circuit which allows the feed from fuse 13 to flow 
through the internal switch, then to the HRW switch on an NP wire. The feed illuminates the 
HRW switch indicator light and is earthed from the switch to earth header C0017 LHD/C0018 
RHD on a B wire, via header C0760.
The feed from fuse 29 is connected to a second internal switch within the BCU. When the 
HRW switch is operated, the completed earth path closes the internal switch. This 
completes an earth path from the coil of the heated rear screen relay, through the Intelligent 
Driver’s Module (IDM) and from the passenger compartment fusebox to the BCU on an SK 
wire, via header C0293 LHD/C0292 RHD. This connection is the serial data bus between 
the IDM and the BCU.
The BCU earth is connected from the BCU to earth header C0551 on a B wire. The IDM is 
also connected to earth header C0551 on a B wire from the passenger compartment 
fusebox.
The completed earth path energises the heated rear screen relay, closing the contacts and 
allowing the feed from fuse 8 in the passenger compartment fusebox to flow through the 
contacts.
The feed flows from the passenger compartment fusebox to the rear screen heater element 
on an NP wire.
The rear screen heater element is connected to earth header C0706 on a B wire.< /PARA>
The momentary operation of the non-latching HRW switch, signals internal electronic 
switches within the BCU to close. Internal circuitry within the BCU holds the switches closed 
for a pre-determined period or until the HRW switch is pushed a second time. 
						

							DESCRIPTION AND OPERATION
4.94DISCOVERY SERIES II
Air Temperature Control (ATC) ECU Operation
On vehicles fitted with air conditioning, the HRW can be operated when DEF, feet/screen 
or screen is selected on the ATC control panel.
When one of the above selections is made, the ATC ECU provides a feed to the HRW switch 
into the NP wire from the BCU to the HRW switch. This illuminates the switch indicator light.
Simultaneously, the ATC ECU also provides an earth path into the NB wire from the BCU to 
the HRW switch. This earth path allows the internal electronic switches within the BCU to 
close, powering the rear screen heater element as described previously. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.95
HEATED FRONT SCREEN (HFS)
DESCRIPTION
General
The heated front screen (HFS) is operated from a non-latching switch located to the left of 
the instrument pack. The switch has an indicator light to show when the HFS is operating. 
The HFS comprises two elements laminated in the screen, each element being controlled 
by a separate fuse. The HFS will only function with the engine running, due to the high 
current draw and subsequent load on the battery.
The HFS can also be operated by the air temperature control ECU on vehicles fitted with air 
conditioning.
OPERATION
Heated Front Screen Supply
Circuit supply
A feed from the battery positive terminal is connected by an R wire to the engine 
compartment fusebox, where it passes through fusible links 1, 7, 8 and fuse 13. Fusible links 
1 and 7 are connected in series.
A feed from fusible link 1 is connected to the contacts of the heated front screen relay in the 
engine compartment fusebox.
A feed from fusible links 1 and 7 is connected to the contacts of the auxiliary circuits relay in 
the engine compartment fusebox.
A feed from fuse 13 is connected from the engine compartment fusebox to the Body Control 
Unit (BCU) on a PN wire.
A feed from fusible link 8 in the engine compartment fusebox 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
When the ignition switch is in position I or II, the feed from fusible link 8 flows through the 
ignition switch to the passenger compartment fusebox on an LGW wire. The feed continues 
through fuse 26 in the passenger compartment fusebox and is connected on an LG wire to 
the coil of the auxiliary circuits relay in the engine compartment fusebox. 
						

							DESCRIPTION AND OPERATION
4.96DISCOVERY SERIES II
In this condition, the auxiliary circuits relay coil is energised and the contacts close. The relay 
coil is earthed to earth header C0018 on a B wire from the engine compartment fusebox, via 
header C0286 LHD/C0288 RHD.
When the ignition switch is 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 
29 in the passenger compartment fusebox and is connected to the BCU on a GU wire.
Heated Front Screen Operation
When the HFS switch is operated, an earth path is completed from the HFS switch to earth 
header C0017 LHD/C0018 RHD on a B wire, via header C0760.
The completion of the earth path from the HFS switch, completes an earth path from the 
BCU to the switch on a KO wire. The earth path completes a circuit within the BCU for an 
internal electronic switch which receives its feed from fuse 29.
The internal switch closes, completing a circuit which allows the feed from fuse 13 to flow 
through the internal switch, then to the HFS switch on a PS wire. The feed illuminates the 
HFS switch indicator light and is earthed from the switch to earth header C0017 LHD/C0018 
RHD on a B wire, via header C0760.
The feed from fuse 29 is connected to a second internal switch within the BCU. When the 
HFS switch is operated, the completed earth path closes the internal switch. This completes 
the connection from the heated screen relay coil to the BCU on a KN wire. The earth path 
from the BCU is on a B wire to earth header C0551.
The completed earth path energises the heated screen relay, closing the relay contacts, 
allowing the feed from fusible link 1 to flow through the relay contacts to fuses 7 and 8.
The feed from fuse 7 is connected to the LH front screen element on a PS wire. The LH front 
screen element is connected to earth header C0018 LHD/C0017 RHD on a B wire.
The feed from fuse 8 is connected to the RH front screen element on a PK wire. The RH 
front screen element is connected to earth header C0017 LHD/C0018 RHD on a B wire.
The momentary operation of the non-latching HFS switch, signals internal switches in the 
BCU to close. Electronics within the BCU holds the switches closed for a pre-determined 
period or until the HFS switch is pushed a second time. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.97
Air Temperature Control (ATC) ECU operation
On vehicles fitted with air conditioning, the HFS can be operated when DEF, feet/screen 
or screen is selected on the ATC control panel.
When one of the above selections is made, the ATC ECU provides a feed to the HFS switch 
into the PS wire from the BCU to the switch. This illuminates the HFS switch indicator light.
Simultaneously, the ATC ECU also provides an earth path into the KO wire from the BCU to 
the HFS switch. This earth path allows the internal electronic switches within the BCU to 
close, powering the front screen elements as described previously. 
						

							DESCRIPTION AND OPERATION
4.98DISCOVERY SERIES II
FRONT WIPERS AND WASHERS
DESCRIPTION
General
The front wipers and washers are operated from a switch stalk located on the right hand side 
of the steering column and operate with the ignition switch in positions I or II. The wipers are 
operated by a wiper motor located below the windscreen plenum. The washers and optional 
headlamp power washers are operated from electric pumps attached to the washer 
reservoir located in the left hand wheel arch.
The electrical wiper and washer functions are controlled by the Body Control Unit (BCU) and 
the Intelligent Driver’s Module (IDM).
The stalk switch selects all operations of the front wipers and washers. A rotary switch on 
the end of the stalk selects the wipers in the off, intermittent slow and fast speeds. A rotary 
wiper delay switch on the stalk has five positions to select the frequency of the intermittent 
function. The BCU determines the resistance through the delay switch and functions the 
wipers at the required interval, depending on switch position.
The stalk can be pulled towards the steering wheel to select the washer function. When the 
washers are operated, the wipers will also operate for three full cycles. The stalk can also 
be pushed down to operate the flick wipe function.
On vehicles fitted with headlamp powerwash, if the headlights are on when the washer 
function is selected, the headlamp powerwash will also operate. The BCU will supply an 
earth path for the coil of the power wash relay, located in the engine compartment fusebox, 
for a period of 0.5 seconds from when the washer function is selected. The powerwash 
function only operates on alternate washer function requests.
The stalk can be moved downwards to operate the wipers. A single push downwards will 
operate the wiper for one full cycle at slow speed. If the switch is pushed and held, the wipers 
operate at fast speed until the switch is released. When the switch is released, the wipers 
will finish their cycle at slow speed. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.99
OPERATION
Front Wipers and Washers 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 links 1, 7, 8, 10 and fuse 4. Fusible 
link 1 and fuse 4 and fusible links 1 and 7 are connected in series.
A feed from fusible link 1 and fuse 4 is connected to the contacts of the power wash relay 
located in the engine compartment fusebox (P108).
A feed from fusible links 1 and 7 is connected to the contacts of the auxiliary circuits relay 
located in the engine compartment fusebox.
A feed from fusible link 8 is connected from the fusebox, on an NW wire, to the passenger 
compartment fusebox and from the fusebox to the ignition switch on an N wire.
A feed from fusible link 10 is connected from the fusebox, on an NP wire to the lighting 
switch.
Ignition switch supply
With the ignition switch in position I or II, the feed from fusible link 8 passes through the 
ignition switch to the passenger compartment fusebox on an LGW wire, where it passes 
through fuse 26.
From fuse 26, the feed is connected on an LG wire to the engine compartment fusebox 
where it is connected to the coil of the auxiliary circuits relay.
The coil of the auxiliary circuits relay is connected from the engine compartment fusebox via 
header C0286 LHD/C0288 RHD, to earth header C0018 on a B wire. The feed from the 
ignition switch energises the auxiliary circuits relay coil, closing the relay contacts.
The closed contacts of the auxiliary circuits relay allow the feed from fusible link 7 to pass 
through the auxiliary circuits relay and connect from the engine compartment fusebox to the 
passenger compartment fusebox on a WG wire, where it passes through fuse 19. The feed 
is also connected to the coil of the powerwash relay in the engine compartment fusebox.
Front Wipers and Washers Operation
The IDM is connected to pin C0661-1 of the BCU via header C0293 LHD/C0292 RHD on an 
SK wire. This connection is the serial data bus between the IDM and BCU.