2002 LAND ROVER DISCOVERY fuse box

ENGINE MANAGEMENT SYSTEM - TD5
DESCRIPTION AND OPERATION 18-1-25
Main relay
The main relay is located in the engine compartment fuse box and supplies battery voltage to the following:
lECM.
lMAF.
lFuel pump relay.
lCruise control master switch.
lCruise control RES switch.
lCruise control SET+ switch.
It is a 4 pin normally open relay and must be energised to provide voltage to the ECM.
Input/Output
The earth path for the main relay is via a transistor within the ECM. When the earth path is completed, the main relay
energises to supply battery voltage to the ECM. Interrupting this earth path de-energises the main relay, preventing
battery voltage reaching the ECM.
Input to the main relay is via pin 1 of connector C0632, located at the engine compartment fuse box. Output from the
main relay is via fuse 1 to the ECM connector C0658 pins 3, 22 and 27. The earth path is via pin 21 of ECM connector
C0658.
The main relay can fail in the following ways:
lRelay open circuit.
lShort circuit to vehicle supply.
lShort circuit to vehicle earth.
lBroken return spring.
In the event of a main relay failure any of the following symptoms may be observed:
lEngine will crank but not start.
lIf the engine is running it will stop.
For the ECM start up to take place the ignition 'on' (position II) voltage must be greater than 6.0 volts.

ENGINE MANAGEMENT SYSTEM - TD5
18-1-28 DESCRIPTION AND OPERATION
Exhaust Gas Regulator (EGR) modulator
The EGR modulator is located in the engine compartment on the offside inner wing. It regulates the vacuum source
to the EGR valve allowing it to open or close. The ECM utilises the EGR modulator to control the amount of exhaust
gas being recirculated in order to reduce exhaust emissions and combustion noise. Optimum EGR is usually obtained
when the vehicle is operating at light throttle openings, and the vehicle is cruising at approximately 2000 to 3000 rev/
min.
Input/Output
The EGR modulator receives battery voltage from fuse 2 in the engine compartment fuse box. The earth path is via
pin 3 of ECM connector C0158. The length of time that the ECM supplies an earth is how long the exhaust gases are
allowed to recirculate. The ECM decides how long to supply the earth for by looking at engine temperature and engine
load.
The EGR can fail in the following ways:
lSolenoid open circuit.
lShort circuit to vehicle supply.
lShort circuit to earth.
In the event of an EGR modulator failure the EGR system will become inoperative.
The MIL will not illuminate in the event of an EGR modulator failure.

ENGINE MANAGEMENT SYSTEM - TD5
DESCRIPTION AND OPERATION 18-1-31
The purpose of the glow plugs is:
lAssist cold engine start.
lReduce exhaust emissions at low engine load/speed.
The main part of the glow plug is a tubular heating element that protrudes into the combustion chamber of the engine.
The heating element contains a spiral filament that is encased in magnesium oxide powder. At the tip of the tubular
heating element is the heater coil. Behind the heater coil and connected in series is a control coil. The control coil
regulates the heater coil to ensure that it does not overheat and cause a possible failure. The glow plug circuit has its
own control relay located in the engine compartment fuse box.
Pre-heat is the length of time the glow plugs operate prior to engine cranking. The ECM controls the pre-heat time of
the glow plugs based on battery voltage and coolant temperature information via the glow plug relay.
Post-heat is the length of time the glow plugs operate after the engine starts. The ECM controls the post-heat time
based on ECT information. If the ECT fails the ECM will operate pre/post-heat time strategies with default values from
its memory. The engine will be difficult to start.
Input/Output
The glow plugs receive voltage from the glow plug relay that is controlled by the ECM. The ECM provides the earth
path for the relay coil closing the relay contacts and supplying the glow plugs with battery voltage. The supply voltage
heats the coils to approximately 1000
°C (1832 °F). The glow plug circuit is wired in parallel, the body of each glow
plug is screwed directly into the engine block which provides each glow plug with an earth path.
The glow plugs can fail in the following ways:
lHeater coil open circuit.
lControl coil open circuit.
lPoor earth quality.
lShort circuit to vehicle supply.
lShort circuit to vehicle earth.
lWiring loom fault.
lRelay windings open circuit.
lIncorrect relay fitted.
In the event of a glow plug failure any of the following symptoms may be observed:
lDifficult starting.
lExcessive smoke emissions after engine start.

ENGINE MANAGEMENT SYSTEM - TD5
DESCRIPTION AND OPERATION 18-1-43
Air Conditioning (A/C)
The ECM controls operation of the A/C compressor and the engine's electric cooling fan in response to requests from
the Automatic Temperature Control (ATC) ECU.
A/C request
When the ATC ECU supplies the ECM with an A/C request, the ECM energises the compressor clutch relay. The
compressor clutch relay is located in the engine compartment fuse box. It is a four pin normally open relay. This means
that the relay must be energised to drive the compressor clutch. During periods of high driver demand such as hard
acceleration or maximum rev/min the ECM will disable the compressor clutch for a short time. This is to reduce the
load on the engine.
The operation of the A/C request is via a switch being connected to earth. Voltage is supplied via pin 9 of connector
C0658 of the ECM, at the point at which the switch is pressed the connection to the earth path is made and the
compressor clutch is engaged.
The ECM provides the earth for the relay windings to allow the compressor clutch relay contacts to close and the
compressor clutch drive to receive battery voltage. The ECM uses a transistor as a switch to generate an open circuit
in the earth path of the relay windings. When the ECM closes down the earth path, the return spring in the relay will
pull the contacts apart to shut down the compressor clutch drive. Fuse 6, located in the engine compartment fuse box,
provides voltage to the compressor clutch relay switching contacts. The relay windings are supplied with battery
voltage from the main relay, also located in the engine compartment fuse box. The earth path for the relay windings
is via pin 29 of the ECM connector C0658. When the relay is energised the output from the switching contacts is
directly to the compressor clutch.
Cooling fan request
The A/C fan request is an input to the ECM from the ATC ECU to request that the engine's electric cooling fan is
activated to provide additional cooling for the A/C condenser.
The cooling fan relay is located in the engine compartment fuse box and is also controlled by the ECM. It is a four pin
normally open relay. This means that the relay must be energised to drive the cooling fan. The cooling fan is used
especially when the engine is operating at excessively high temperatures. It is also used as a part of the ECM backup
strategy if the ECT sensor fails.
The operation of the cooling fan request is via a switch being connected to earth. Voltage is supplied via pin 23 of
connector C0658 of the ECM, at the point at when the switch is pressed the connection to the earth path is made and
the cooling fan is engaged.
The ECM provides the earth for the cooling fan relay windings to allow the relay contacts to close and the cooling fan
motor to receive battery voltage. The ECM uses a transistor as a switch to generate an open circuit in the earth path
of the relay windings. When the ECM closes down the earth path, the return spring in the relay will pull the contacts
apart to shut down the cooling fan motor drive. Input to the A/C cooling fan relay switching contacts is via fuse 4
located in the engine compartment fuse box. The relay windings are supplied with battery voltage from the main relay,
also located in the engine compartment fuse box. The earth path for the relay windings is via pin 4 of the ECM
connector C0658. When the relay is energised the output from the switching contacts is directly to the cooling fan
motor.

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-15
Input/Output
Electrical input to the camshaft position sensor is from fuse 2 located in engine compartment fuse box. One output is
sensor earth, the other is the signal output to the ECM via pin 20 of connector C0636.
The CMP sensor can fail the following ways or supply incorrect signal:
lSensor open circuit.
lShort circuit to vehicle battery supply.
lShort circuit to vehicle earth.
lIncorrect fitting of the sensor.
lExcessive camshaft gear wheel tolerance.
lExcessive camshaft endfloat.
lCamshaft and crankshaft misalignment.
lSpeed signal correlation with CKP sensor signal.
lCam wheel magnetised / residual magnetism
In the event of a CMP sensor signal failure any of the following symptoms may be observed:
lIgnition timing reverts to default values from ECM memory.
lLoss of cylinder correction.
lLoss of active knock control.
lLoss of active knock control diagnostics.
lLoss of cylinder identification for misfire diagnostics.
lLoss of quick synchronisation of crankshaft and camshaft for cranking/ start up.
lFuel injection could be 360
° out of phase.
lFront HO
2S sensor ageing period diagnostic disabled (NAS only)
Should a malfunction of the component occur the following fault code may be evident and can be retrieved by
TestBook:
The fault condition has to be detected for more than 100 cam pulses (25 revolutions) when the engine speed is greater
than 500 rev/min.
Engine Coolant Temperature (ECT) sensor (C0196)
The ECT sensor is located at the front of the engine adjacent to the coolant outlet pipe. The ECT sensor forms a vital
part of the ECM operating strategy, and therefore the optimum control of the running of the engine. Richer air/ fuel
ratio is required at lower coolant temperatures such as cold starting. Coolant temperature information from the ECT
sensor is also vital to enable the ECM to weaken the air/ fuel mixture as temperature rises to maintain low emissions
and optimum performance.
P code J2012 description Land Rover description
P0340 Camshaft position sensor circuit malfunction Open/short circuit to vehicle supply or earth

ENGINE MANAGEMENT SYSTEM - V8
18-2-20 DESCRIPTION AND OPERATION
Should a malfunction occur, the following fault codes may be evident and can be retrieved by TestBook:
Mass Air Flow (MAF)/ Inlet Air Temperature (IAT) sensor (C0149)
The MAF/ IAT sensors are combined into a single unit and located between the air filter housing and the inlet manifold.
The ECM receives input signals from the MAF/ IAT sensor to calculate the mass of air flowing into the engine inlet
manifold.
Input/Output
The MAF sensor has both electrical input and output. Input to the MAF sensor comes from two different sources.
Battery voltage is supplied to the MAF sensor via fuse 2 of the engine compartment fuse box. The MAF sensor also
utilises a 5 volt reference input via pin 7 of connector C0636 of the ECM. The MAF sensor output voltage is measured
via pin 23 of connector C0636 of the ECM.
The IAT sensor has only electrical output. Output from the IAT sensor is measured at pin 34 of connector C0636 of
the ECM, this is a variable voltage/ resistance measured by the sensor to provide air temperature information to the
ECM.
The MAF/ IAT sensor share the same sensor earth. Sensor earth is via pin 9 of connector C0636 of the ECM.
The MAF/ IAT sensor and its connector has silver plated terminals for its low current signals to protect against
corrosion. DO NOT apply 12V to the 5V supply, as this will destroy the internal circuitry. The MAF/IAT sensor should
not be dropped or roughly handled and should be kept free from contamination.
P code J2012 description Land Rover description
P1117 Radiator outlet temperature
thermister lowThermostat reading below -33 °C (-
27 °F)
P1118 Radiator outlet temperature
thermister highThermostat reading above 140 °C
(284 °F)
P0126 Engine thermostat defective Difference in radiator and engine
coolant temperatures too small

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-27
The HO2S uses zirconium contained in a galvanic cell surrounded by a gas permeable ceramic, this produces an
output voltage proportional to the ratio difference between the oxygen in the exhaust gases and to the ambient
oxygen.
The HO
2S operates at approximately 350 °C (662 °F). To achieve this temperature the HO2S incorporate a heating
element which is controlled by a PWM signal from the ECM. The elements are activated immediately after engine
starts and also under low engine load conditions when the exhaust gas temperature is insufficient to maintain the
required HO
2S temperature. If the heater fails, the ECM will not allow closed loop fuelling to be implemented until the
sensor has achieved the required temperature.
This value equates to an HO
2S output of 450 to 500 mV. A richer mixture can be shown as λ = 0.97, this pushes the
HO
2S output voltage towards 1000 mV. A leaner mixture can be shown as λ = 1.10, this pushes the HO2S output
voltage towards 100 mV.
From cold start, the ECM runs an open loop fuelling strategy. The ECM keeps this strategy in place until the HO
2S is
at a working temperature of 350
°C (662 °F). At this point the ECM starts to receive HO2S information and it can then
switch into closed loop fuelling as part of its adaptive strategy. The maximum working temperature of the tip of the
HO
2S is 930 °C (1706 °F), temperatures above this will damage the sensor.
HO
2S age with use, this increases their response time to switch from rich to lean and from lean to rich. This can lead
to increased exhaust emissions over a period of time. The switching time of the upstream sensors are monitored by
the ECM. If a pre-determined threshold is exceeded, a failure is detected and the MIL illuminated.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Exhaust emission control system.
Input/Output
The upstream and downstream HO
2S are colour coded to prevent incorrect fitting. The tips of the upstream sensors
are physically different to the tips of the downstream sensors.
The HO
2S are colour coded as follows:
lUpstream sensors (both banks) - orange.
lDownstream sensors (both banks) - grey.
The four HO
2S have a direct battery supply to the heater via fuse 2 located in the engine compartment fuse box.
The heater is driven by the ECM providing an earth path for the circuit as follows:
lUpstream LH bank via pin 19 of connector C0635 of the ECM.
lUpstream RH bank via pin 13 of connector C0635 of the ECM.
lDownstream LH bank via pin 7 of connector C0635 of the ECM.
lDownstream RH bank via pin 1 of connector C0635 of the ECM.
The HO
2S output signal is measured by the ECM as follows:
lUpstream LH bank via pin 15 of connector C0635 of the ECM.
lUpstream RH bank via pin 16 of connector C0635 of the ECM.
lDownstream LH bank via pin 17 of connector C0635 of the ECM.
lDownstream RH bank via pin 14 of connector C0635 of the ECM.
The HO
2S earth path for the signal is supplied by the ECM as follows:
lUpstream LH bank via pin 9 of connector C0635 of the ECM.
lUpstream RH bank via pin 10 of connector C0635 of the ECM.
lDownstream LH bank via pin 11 of connector C0635 of the ECM.
lDownstream RH bank via pin 8 of connector C0635 of the ECM.
The HO
2S voltage is difficult to measure using a multimeter, the output can be monitored using TestBook. A rich
mixture would read 500 to 1000 mV, a weak mixture would read 100 mV to 500 mV, the reading should switch from
rich to weak. The open loop default voltage is 450 mV, this is used by the ECM to set the air/ fuel ratio until the tip of
the HO
2S reaches operating temperature.

ENGINE MANAGEMENT SYSTEM - V8
18-2-30 DESCRIPTION AND OPERATION
There are eight fuel injectors one per cylinder that the ECM operates sequentially. All the injectors are fed from a
common fuel rail as part of the returnless fuel system. Fuel pressure is maintained at a constant 3.5 bar (52 lbf.in2) by
a regulator that is integral with the fuel pump.

+ FUEL DELIVERY SYSTEM - V8, DESCRIPTION AND OPERATION, Description.
Input/Output
All eight fuel injectors are supplied with battery voltage via fuse number 1 located in engine compartment fuse box.
The ECM controls the individual earth path for each injector via its own pin at connector C0636 of the ECM multiplug.
This facility allows the ECM to control the fuel injectors so that sequential fuel injection can take place.
Typical hot engine injector pulse width values:
lIdle = 2.5 ms.
lPeak torque (3000 rev/min) = 7 ms The ECM controls injector earth as follows:
lCylinder No 1 - pin 41 of connector C0636 of the ECM multiplug.
lCylinder No 2 - pin 1 of connector C0636 of the ECM multiplug.
lCylinder No 3 - pin 27 of connector C0636 of the ECM multiplug.
lCylinder No 4 - pin 40 of connector C0636 of the ECM multiplug.
lCylinder No 5 - pin 2 of connector C0636 of the ECM multiplug.
lCylinder No 6 - pin 15 of connector C0636 of the ECM multiplug.
lCylinder No 7 - pin 14 of connector C0636 of the ECM multiplug.
lCylinder No 8 - pin 28 of connector C0636 of the ECM multiplug.
Individual injectors can be measured for resistance using a multimeter. An acceptable injector resistance is as follows:
l14.5
± 0.7 ohms at 20 °C (68 °F).
The fuel injectors can fail in the following ways or supply incorrect signal:
lInjector actuator open circuit.
lShort circuit to vehicle supply.
lShort circuit to vehicle earth.
lBlocked injector.
lRestricted injector.
lLow fuel pressure.
In the event of fuel injector signal failure any of the following symptoms may be observed:
lRough running.
lDifficult starting.
lEngine misfire.
lPossible catalyst damage.
lHigh emissions.
lAdaptive fuelling disabled.
lAdaptive idle speed control disabled.
The ECM performs three types of fuel injector diagnostic check:
lOutput short circuit to earth
lOutput short circuit to battery voltage
lOutput open circuit
Should a malfunction of the component occur the following fault codes may be evident and can be retrieved by
TestBook:
P Code J2012 Description Land Rover Description
P0201 Injection circuit malfunction - cylinder 1 Injector 1 open circuit
P0261 Cylinder 1 injector circuit low Injector 1 short circuit to earth
P0262 Cylinder 1 injector circuit high Injector 1 short circuit to battery supply
P0301 Cylinder 1 misfire detected Injector 1 excess emissions/catalyst damaging level of
misfire
P0202 Injection circuit malfunction - cylinder 2 Injector 2 open circuit
P0264 Cylinder 2 injector circuit low Injector 2 short circuit to earth
P0265 Cylinder 2 injector circuit high Injector 2 short circuit to battery supply