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

							DESCRIPTION AND OPERATION
4.70DISCOVERY SERIES II
ANTI-LOCK BRAKING SYSTEM (ABS)
DESCRIPTION
General
ABS is controlled by the Self Levelling and Anti-lock Braking System (SLABS) ECU. The 
ABS system comprises the ECU, ABS wheel sensors and an ABS modulator. The ABS 
system also controls electronic brake distribution, hill descent control, centre differential lock 
control and electronic traction control. Refer to Workshop Manual - Description and 
Operation for further details.
NOTE: This Description and Operation applies to vehicles without Self Levelling Suspension 
(SLS). For vehicles with SLS refer to the SLABS Description and Operation in this manual.
OPERATION
ABS 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 8 and 11 and fuse 11.
The feed from fusible link 8 is connected to the passenger compartment fusebox on an NW 
wire and from the fusebox to the ignition switch on an N wire.
The feed from fusible link 11 is connected to the contacts of the ABS return pump relay in 
the engine compartment fusebox.
The feed from fuse 11 is connected to the SLABS ECU pin C0504-1 on an NK 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 and passes through fuses 25, 27 
and 28.
From fuse 25 the feed is connected to the contacts of the hill descent relay. The feed from 
fuse 25 is also connected on a GY wire to the reverse lamp switch (manual gearbox 
vehicles) or the starter inhibitor/reverse lamp switch (automatic gearbox vehicles). When the 
switch is operated, the feed is connected on a GN wire, through header joint C0287 LHD/
C0294 RHD, to the SLABS ECU pin C0504-7.
From fuse 27 the feed is connected, via header joint C0760, on an LG wire to the hill descent 
switch. When the hill descent switch is operated the feed continues from the switch on a PS 
wire to the SLABS ECU pin C0504-14.
From fuse 28 the feed is connected on an LG wire to the SLABS ECU pin C0504-2. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.71
ABS Operation
HDC Brake lamp operation
When the hill descent control operates, the SLABS ECU pin C0506-12 provides a power 
supply on a BG wire to the coil of the hill descent relay in the passenger compartment 
fusebox. The relay coil energises and the contacts close. The earth path from the coil is from 
the passenger compartment fusebox on a B wire to earth header C0017 LHD/C0018 RHD.
The feed from fuse 25 in the passenger compartment fusebox passes through the closed 
relay contacts and is connected from the fusebox on a GP wire, through header C0287 LHD/
C0290 RHD to header C0295.
The feed is then connected to the LH tail lamp on a GP wire and illuminates the brake lamp 
bulb. The feed is also connected from the header C0295 to header C0723 on a GP wire. 
From the header C0723, the feed is connected on GP wires to the RH tail lamp, the high 
mounted brake lamp and the trailer socket, illuminating the brake lamp bulbs.
ABS return pump operation
When the ABS or other ABS related functions operate, the SLABS ECU pin C0506-15 
provides a power supply on a WO wire to the coil of the ABS return pump relay in the engine 
compartment fusebox. The relay coil energises and the relay contacts close. The earth path 
from the coil is from the engine compartment fusebox on a B wire, via header C0286 LHD/
C0288 RHD to earth header C0018.
The feed from fusible link 11 in the engine compartment fusebox passes through the closed 
contacts and is connected from the fusebox on an NR wire to splice joint A306. The feed 
continues from splice joint A306 on an NR wire to the SLABS ECU pin C0504-8. The feed 
is also connected from the splice joint A306 on an NR wire to the ABS return pump. The 
earth path from the ABS return pump is on a B wire to earth eyelet connector C0562-1.
Differential lock unit switch operation
When the differential lock unit switch is operated, an earth path is completed from the 
SLABS ECU pin C0506-9, via header C0761, to the differential lock unit switch on a BU wire.
On vehicles with automatic transmission the earth path is completed from the switch on a B 
wire to splice joint SJ2. From the splice joint the earth is connected on a B wire to earth 
header C0552.
On vehicles with manual transmission, the earth path is completed from the switch on a B 
wire to splice joint A33. From the splice joint the earth is connected on a B wire to earth 
header C0552.
When the differential lock unit switch completes the earth path, the SLABS ECU interprets 
the earth as a signal. Simultaneously, the closure of the switch also completes an earth path 
from the instrument pack on a BU wire to header C0761, through the differential lock unit 
switch to the earth header C0552. This earth is used by the instrument pack to illuminate the 
differential lock warning lamp. 
						

							DESCRIPTION AND OPERATION
4.72DISCOVERY SERIES II
Transmission high/low switch operation
When the transmission high/low switch is operated, an earth path is completed from the 
SLABS ECU pin C0504-11, via header C0290 LHD/C0288 RHD to the transmission high/
low switch on an RK wire.
On vehicles with automatic transmission, the earth path is completed from the switch on a 
B wire to splice joint SJ2. From the splice joint the earth is connected on a B wire to earth 
header C0552.
On vehicles with manual transmission, the earth path is completed from the switch on a B 
wire to splice joint A33. From the splice joint the earth is connected on a B wire to earth 
header C0552.
When the transmission high/low switch completes the earth path, the SLABS ECU interprets 
the earth as a signal to confirm that the transfer box is in low range.
ABS sensors
The SLABS ECU receives inputs from each wheel speed sensor through connector C0505. 
The inputs are as follows:
zFrom Front LH ABS sensor pins C0516-1/2 to SLABS ECU pins C0505-1/2 on G wires
zFrom Front RH ABS sensor pins C0517-1/2 to SLABS ECU pins C0505-4/5 on G wires
zFrom Rear LH ABS sensor pins C0502-1/2 to SLABS ECU pins C0505-7/8 on W wires
zFrom Rear RH ABS sensor pins C0503-1/2 to SLABS ECU pins C0505-3/6 on W wires.
ABS modulator
The SLABS ECU provides outputs to and receives inputs from the ABS modulator through 
connector C0506. The inputs and outputs are as follows:
zOutput from SLABS ECU pin C0506-1 to ABS modulator pin C0501-1 on an SW wire
zOutput from SLABS ECU pin C0506-2 to ABS modulator pin C0501-2 on an SR wire
zInput from ABS modulator pin C0501-8 to SLABS ECU pin C0506-3 on a BS wire
zOutput from SLABS ECU pin C0506-4 to ABS modulator pin C0501-13 on an SG wire
zOutput from SLABS ECU pin C0506-5 to ABS modulator pin C0501-12 on an SU wire
zInput from ABS modulator pin C0501-9 to SLABS ECU pin C0506-6 on a YG wire
zOutput from SLABS ECU pin C0506-7 to ABS modulator pin C0501-5 on an SY wire
zOutput from SLABS ECU pin C0506-8 to ABS modulator pin C0501-4 on an SN wire
zOutput from SLABS ECU pin C0506-10 to ABS modulator pin C0501-10 on an SP wire
zOutput from SLABS ECU pin C0506-11 to ABS modulator pin C0501-11 on an SK wire.
The ABS modulator (D124) is connected on a B wire to earth eyelet connector C0561-1. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.73
Instrument pack
The SLABS ECU provides outputs to the instrument pack through connector C0504. The 
outputs are as follows:
zFrom SLABS ECU pin C0504-16 to instrument pack pin C0233-5 on a WY wire (HDC 
warning lamp)
zFrom SLABS ECU pin C0504-17 to instrument pack pin C0233-10 on a WK wire (HDC 
info warning lamp)
zFrom SLABS ECU pin C0504-18 to instrument pack pin C0233-3 on a WR wire (ABS 
warning lamp)
zFrom SLABS ECU pin C0504-13 to instrument pack pin C0233-4 on a WU wire ( TC 
warning lamp)
zFrom SLABS ECU pin C0504-9, via header joint C0293 LHD/C0285 RHD on a KO wire 
(brake warning lamp).
The instrument pack is also connected from the instrument pack pin C0233-16 on an SK 
wire, via header C0292 LHD/C0290 RHD to the IDM in the passenger compartment 
fusebox. The SK wire is the serial data bus between the IDM and the instrument pack.
Diagnostic socket
The SLABS ECU provides outputs and receives inputs from the diagnostic socket through 
connector C0504. Connector pin C0504-5 is connected on a K wire, via header C0286 to 
the diagnostic socket pin C0040-7.
Body Control Unit (BCU)
The SLABS ECU pin C0504-15 receives an input from the BCU pin C0662-10 on a GB wire. 
This signal is used by the ABS system for automatic transmission in neutral for HDC control.
Engine Control Module (ECM)
On V8 engine vehicles the SLABS ECU outputs a rough road signal to the ECM from SLABS 
ECU pin C0504-4 on an RG wire to ECM pin C0637-34. The rough road signal inhibits 
misfire detection on NAS vehicles. The SLABS ECU receives engine data from the ECM 
from ECM pin C0636-29 on an SP wire to SLABS ECU pin C0504-10.
On Td5 engine vehicles the SLABS ECU receives engine data from ECM pin C0658-32 on 
an SP wire to SLABS ECU pin C0504-10. 
						

							DESCRIPTION AND OPERATION
4.74DISCOVERY SERIES II
Road speed signal
The SLABS ECU outputs a road speed signal from pin C0504-3 on a KG wire to header 
C0290. From header C0290 the road speed signal is passed on KG wires to the following 
ECU pins:
zCruise control ECU pin C0239-15
zEngine Control Module (ECM pin C0637-22 on V8 engine vehicles and pin C0658-13 
on Td5 engine vehicles
zActive Cornering Enhancement (ACE) ECU pin C0647-5
zICE Tuner/Amplifier pin C0491-20
zInstrument pack pin C0230-16
zAir Temperature Control (ATC) ECU pin C0792-2 via splice joint A87. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.75
SUPPLEMENTARY RESTRAINT SYSTEM (SRS)
DESCRIPTION
General
The Supplementary Restraint System (SRS) provides additional protection for front seat 
occupants during a frontal collision above a preset severity.
The system is operational only with the ignition switch in position II. With the ignition on, any 
frontal collision is detected by an accelerometer and a mechanical safing sensor within the 
airbag DCU. If the impact is above the preset severity, the airbag DCU transmits 
simultaneous signals to fire the airbag modules and seat belt pretensioners. The airbag 
modules deploy protective airbags in front of the driver and front seat passenger and the 
seat belt pretensioners retract to tighten the front seat belts.
The airbag DCU can store fault codes for the DCU, the driver and passenger airbag modules 
and the pretensioners. These fault codes can be accessed using TestBook/T4 via the 
diagnostic socket.
The airbag DCU is located below the centre console near the handbrake mounting. The 
driver airbag is located in the centre of the steering wheel and the passenger airbag is 
located in the fascia, above the glovebox. The seat belt pretensioners are located with the 
seat belt anchorages.
An SRS warning LED is located in the instrument pack. When the ignition switch is turned 
to position II, the LED will be illuminated for 3 to 5 seconds to confirm LED operation. If a 
fault in the SRS system occurs, the LED will be illuminated for the duration of the fault or for 
a period of between 8 to 16 seconds.
The airbag DCU can supply a low voltage test current to the airbags and pretensioners to 
check circuit continuity. The DCU can also detect shorts, shorts to ground or battery and 
open circuits. These conditions can be retrieved using TestBook/T4.
WARNING: Never use multimeters or other general purpose test equipment on SRS 
system components or connectors. System faults should be diagnosed through the 
use of recommended test equipment only. 
						

							DESCRIPTION AND OPERATION
4.76DISCOVERY SERIES II
OPERATION
SRS 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.
A feed from fusible link 8 is connected on an NW wire to the passenger compartment 
fusebox and from the fusebox to the ignition switch (S176) 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 fuse 35 in the passenger compartment fusebox on a Y wire. G wires connect fuse 
35 in the passenger compartment fusebox to the instrument pack and the airbag DCU.
The SRS warning lamp is connected from the instrument pack to the airbag DCU on a YR 
wire. If a failure of the LED or connecting wiring occurs, the airbag DCU detects a 0V 
condition on the YR wire and stores a fault code in the DCU memory.
The airbag DCU is connected to earth eyelet connector C0360-1 on a B wire.
SRS Connections
Diagnostic socket
The diagnostic socket is connected to the airbag DCU on a K wire via header C0286. The 
airbag DCU can send/receive digital outputs and inputs to/from TestBook/T4 for diagnostic 
interrogation.
LH pretensioner
The LH pretensioner is connected to the airbag DCU on an OR wire and an O wire. The OR 
wire supplies a negative digital output and the O wire supplies a positive digital output for 
pretensioner operation.
RH pretensioner
The RH pretensioner is connected to the airbag DCU on an N wire and an NR wire. The N 
wire supplies a positive digital output and the NR wire supplies a negative digital output for 
pretensioner operation.
Passenger airbag
The passenger airbag is connected to the airbag DCU on a WY wire and a W wire. The WY 
wire supplies a positive digital output and the W wire supplies a negative digital output for 
airbag operation.
Driver airbag
The driver airbag is connected, via the rotary coupler, to the airbag DCU on an RY wire and 
an R wire. The RY wire supplies a negative digital output and the R wire supplies a positive 
digital output for airbag operation. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.77
AIR CONDITIONING (A/C)
DESCRIPTION
General
The air conditioning (A/C) can only be operated with the engine running. The A/C is selected 
using the Air Temperature Control (ATC) panel on the fascia. The A/C system controls the 
temperature, distribution and volume of air supplied to the vehicle interior. The system is 
electronically controlled with automatic and manual modes of operation. The system also 
features separate temperature control of the LH and RH air outlets.
Rear A/C is an optional fitment and provides additional cooling by recirculating air through a 
second evaporator.
The cooling fan is used by the ATC ECU for A/C condensor cooling and also by the ECM for 
engine cooling. Refer to cooling fan Description and Operation in this manual for ECM 
operation.
Operation of the A/C system is dependant on various conditions being correct, i.e. engine 
coolant temperature, engine speed, vehicle speed, A/C dual cut-off switch etc. For further 
details of A/C operating parameters refer to the Workshop Manual Air Conditioning 
Description and Operation.
OPERATION
Air Conditioning Supply
Circuit supply
A feed from the battery positive terminal is connected on an R wire to the engine 
compartment fusebox. The feed passes through fusible links 1, 3, 4 and 8 and fuses 5, 6 and 
13. Fusible links 1 and 4 are connected in series. Fuses 5 and 6 are also connected in series 
with fusible link 1.
The feed from the battery is also connected directly to the contacts of the main relay in the 
engine compartment fusebox.
From fusible link 3 is connected on an NR wire to the passenger compartment fusebox 
where it passes through fuse 20.
The feed from fusible link 4 is connected on an NK wire to the passenger compartment 
fusebox where it passes through fuses 6 and 7.
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. 
						

							DESCRIPTION AND OPERATION
4.78DISCOVERY SERIES II
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 W wire and passes through fuse 31.
From fuse 31 the feed passes on a GK wire to splice joint A9/A144. From the splice joint the 
feed is divided into three separate feeds as follows:
zA GK wire supplies power to the Air Temperature Control (ATC) ECU.
zA GR wire supplies power to the in-car temperature sensor.
zA GR wire to connector interface C0765-1/C0778-1 changes to a LGW wire to splice 
joint A1. From splice joint A1 the feed is connected on a LGW wire to the fresh/
recirculated air mode motor. A tapping from splice joint A1 passes on a LGW wire, via 
splice joint B1, to the coil of the blower relay. From splice joint B1 a second LGW wire 
is connected to the coil of the power relay.
Front Air Conditioning Operation
Air temperature control ECU supply
A feed from fusible link 3 in the engine compartment fusebox is connected on an NR wire to 
the passenger compartment fusebox. The feed passes through fuse 20 and is connected, 
via header C0725, to the Air Temperature Control ECU on a P wire.
Main relay/inertia switch supply
A feed from fuse 13 in the engine compartment fusebox is connected to the inertia switch by 
a NB wire. When the inertia switch is closed (not tripped), the feed continues on a WG wire 
to the coil of the main relay in the engine compartment fusebox. The main relay coil is then 
connected from the relay to the Engine Control Module (ECM)) on a UR wire. When 
conditions are correct, the ECM provides the earth path which in turn energises the main 
relay, closing the contacts.
Cooling fan relay supply
A feed from fuse 5 in the engine compartment fusebox, is connected to the contacts of the 
cooling fan relay.
Cooling fan motor operation
When the main relay is energised, a feed passes from the relay contacts to the coil of the 
cooling fan relay. The cooling fan relay coil is earthed on a BP wire (Td5 engines) or a GW 
wire (V8 engines) to the ECM.
When conditions are correct, the ECM provides the earth path which energises the cooling 
fan relay coil closing the contacts. The feed from fuse 5 in the engine compartment fusebox 
passes through the cooling fan relay contacts and from the fusebox to the cooling fan motor 
on a BN wire. The feed operates the cooling fan motor which is connected to earth header 
C0018 on a B wire. 
						

							DESCRIPTION AND OPERATION
DISCOVERY SERIES II 4.79
Air conditioning compressor clutch relay supply
A feed from fuse 6 in the engine compartment fusebox, is connected to the contacts of the 
air conditioning compressor clutch relay.
Air conditioning compressor clutch operation
When the main relay is energised, a feed passes from the relay contacts to the coil of the air 
conditioning compressor clutch relay. The compressor clutch relay coil is earthed on a BS 
wire to the ECM.
When conditions are correct, the ECM provides the earth path which in turn energises the 
compressor clutch relay coil closing the contacts. The feed from fuse 6 in the engine 
compartment fusebox passes through the relay contacts and from the fusebox is connected 
on a BG wire to the air conditioning compressor clutch. The feed operates the air 
conditioning compressor clutch which is connected to earth header C0018 (Td5 engines) or 
earth eyelet connector C0807-1 (V8 engines).
Fresh/recirculated air mode motor
The feed from fuse 31 in the passenger compartment fusebox passes on a GK wire to splice 
joint A9/A144. From the splice joint the feed passes on a GR wire to connector interface 
C0765-1/C0778-1. From the connector interface the feed passes, via splice joint A1, to the 
fresh/recirculated air mode motor on a LGW wire.
The fresh/recirculated air mode motor is connected to the Air Temperature Control (ATC) 
ECU on an RG wire to ECU pin C0793-8 and on a UB wire to ECU pin C0793-16.
Blower relay
The feed from fuse 31 in the passenger compartment fusebox passes on a GK wire to splice 
joint A9/A144. From the splice joint the feed passes on a GR wire to connector interface 
C0765-1/C0778-1. From the connector interface the feed passes, via splice joint A1, to the 
coil of the blower relay. The coil is connected on an N wire to pin C0793-2 of the ATC ECU.
When blower relay (R176) operation is required, the ATC ECU completes an earth path for 
the relay coil, energising the relay and closing the contacts. A feed from fuse 7 in the 
passenger compartment fusebox is connected on an NR wire to contacts of the blower relay. 
The feed passes through the relay contacts and is connected on a WR wire to the front 
blower motor. The front blower motor is connected on a B wire to the power relay and the 
power transistor via splice joint A10.
The contact of the blower relay is also connected on a B wire, via splice joint B9, to earth 
eyelet connector C0910-1. When the relay is connected to the earth, the front blower motor 
power feed will be removed preventing motor operation.