2002 LAND ROVER DISCOVERY fuse box

ENGINE MANAGEMENT SYSTEM - V8
18-2-32 DESCRIPTION AND OPERATION
Idle Air Control Valve (IACV) (C0641)
The IACV is located on the side of the air inlet pipe on top of the engine. The IACV is used to maintain good quality
idle speed under all operating conditions.
When an engine is running at idle it is subject to a combination of internal and external loads that can affect idle speed.
These loads include engine friction, water pump, alternator operation, and air conditioning.
The IACV acts as an air bypass valve. The ECM uses the IACV to enable the closed loop idle speed calculation to be
made by the ECM. This calculation regulates the amount of air flow into the engine at idle, therefore compensating
for any internal or external loads that may affect idle speed.
The IACV utilises two coils that use opposing PWM signals to control the position of opening/closing of a rotary valve.
If one of the circuits that supply the PWM signal fails, the ECM closes down the remaining signal preventing the IACV
from working at its maximum/ minimum setting. If this should occur, the IACV automatically resumes a default idle
position. In this condition, the engine idle speed is raised and maintained at 1200 rev/min with no load placed on the
engine.
The idle speed in cold start condition is held at 1200 rev/min in neutral for 20 seconds and ignition timing is retarded
as a catalyst heating strategy. The cold start idle speed and the default idle position give the same engine speed 1200
rev/min, and although they are the same figure they must not be confused with each other as they are set separately
by the ECM.
Note that the rotary valve must not be forced to move by mechanical means. The actuator can not be
serviced; if defective, the entire IACV must be replaced.
Input/Output
The input to the IACV is a 12 volt signal from fuse 2 located in the engine compartment fuse box. The output earth
signal to open and close the actuator is controlled by the ECM as follows:
lIACV (open signal) - via pin 42 of connector C0636 of the ECM
lIACV (closed signal) - via pin 43 of connector C0636 of the ECM
The IACV can fail the following ways or supply incorrect signal:
lActuator faulty.
lRotary valve seized.
lWiring loom fault.
lConnector fault.
lIntake system air leak.
lBlocked actuator port or hoses.
lRestricted or crimped actuator port or hoses.

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-33
In the event of an IACV signal failure any of the following symptoms may be observed:
lEither low or high idle speed.
lEngine stalls.
lDifficult starting.
lIdle speed in default condition.
There are eight IACV diagnostic checks performed by the ECM:
lOutput short circuit to earth – opening coil
lOutput short circuit to battery supply – opening coil
lOutput open circuit – opening coil
lOutput short circuit to earth – closing coil
lOutput short circuit to battery voltage – closing coil
lOutput open circuit – closing coil
lBlocked IACV – rev/min error low (engine speed must be 100 rev/min less than the target speed, engine load
less than 2.5 and the measured air flow more than 10 kg/h less than the expected air flow for a fault condition to
be flagged).
lBlocked IACV – rev/min error high (the engine speed must be more than 180 rev/min greater than the target
speed and the measured air flow more than 10 kg/h greater than the expected air flow for a fault condition to be
flagged).
Should a malfunction of the component occur, the following fault codes may be evident and can be retrieved by
TestBook.
Fuel pump relay
The fuel pump relay is located in the engine compartment fuse box. It is a 4 pin normally open relay. Input from the
ECM allows the fuel pump relay to control the electrical input to the fuel pump, regulating the fuel supply to the fuel
injectors. When the ignition is switched on and the engine is cranked, the fuel pump relay is activated by the ECM,
allowing the fuel system to be pressurised to 3.5 bar (52 lbf.in
2). The ECM then deactivates the relay until the engine
has started.
If the fuel pump runs, but the fuel pressure is out of limits, adaptive fuel faults will be stored.
P Code J2012 Description Land Rover Description
P1510 IACV opening coil malfunction Short circuit to battery supply - opening winding
P1513 IACV opening coil malfunction Short circuit to earth - opening winding
P1514 IACV opening coil malfunction Open circuit - opening winding
P1553 IACV closing coil malfunction Short circuit to battery supply - closing winding
P1552 IACV closing coil malfunction Short circuit to earth - closing winding
P1551 IACV closing coil malfunction Open circuit - closing winding
P0505 Idle control system malfunction Blocked IACV - high or low rev/min error

ENGINE MANAGEMENT SYSTEM - V8
18-2-34 DESCRIPTION AND OPERATION
Input/Output
The input value for the relay windings is battery voltage, the input value for the switching contacts comes from fuse
10 in the engine compartment fuse box. The output control of the switching contacts is direct to the fuel pump motor,
and the relay windings are controlled by pin number 18 of connector C0635 of the ECM.
At ignition 'on' (position II) the fuel pump relay contacts remain open until the ECM supplies an earth path for the relay
windings via pin number 18 of connector C0635 of the ECM. At this point, the relay windings are energised, drawing
the relay contacts closed. This allows voltage from fuse 10 in the passenger compartment fuse box to pass directly
to the fuel pump.
The fuel pump relay can fail the following ways or supply incorrect signal:
lRelay drive open circuit.
lShort circuit to vehicle earth.
lShort circuit to vehicle supply.
lComponent failure.
In the event of a fuel pump relay failure any of the following symptoms may be observed:
lEngine stalls or will not start.
lNo fuel pressure at the fuel injectors.
The ECM performs three types of diagnostic test to confirm the fuel pump relay integrity:
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.
Evaporative emissions
Refer to Emissions section for description of the evaporative emissions system components.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Evaporative emission control system.
Secondary air injection (NAS only)
Refer to Emissions section for description of the secondary air injection system components.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Secondary air injection system.
Fuel tank pressure sensor (NAS only)
Refer to Fuel Delivery section for description of the fuel system components.

+ FUEL DELIVERY SYSTEM - V8, DESCRIPTION AND OPERATION, Description.
Refer to Emissions section for description of the fuel tank pressure sensor.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Evaporative emission control system.
P Code J2012 Description Land Rover Description
P1230 Fuel pump relay malfunction Fuel pump relay open circuit - not the fuel pump
P1231 Fuel pump relay circuit low Fuel pump relay short circuit to battery supply - not the
fuel pump
P1232 Fuel pump relay circuit high Fuel pump relay short circuit to earth - not the fuel pump

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-35
Ignition coils
Two double ended ignition coils are located at the rear of the engine, below the inlet plenum camber mounted on a
bracket. The ignition system operates on the wasted spark principle. When the ECM triggers an ignition coil to spark,
current from the coil travels to one spark plug jumping the gap at the spark plug electrodes igniting the mixture in the
cylinder. Current continues to travel along the earth path (via the cylinder head) to the spark plug negative electrode
at the cylinder that is on the exhaust stroke. The current jumps across the spark plug electrodes and back to the coil
completing the circuit. Since it has sparked simultaneously in a cylinder that is on the exhaust stroke it has not done
any work, therefore it is wasted.
The coils are paired in the following cylinder order:
l1 and 6.
l8 and 5.
l4 and 7.
l3 and 2.
The ECM calculates the dwell timing from battery voltage, and engine speed to ensure constant secondary energy.
This ensures sufficient spark energy is always available without excessive primary current flow and thus avoiding
overheating or damage to the coils. Individual cylinder spark timing is calculated from the following signals:
lEngine speed.
lEngine load.
lEngine temperature.
lKnock control.
lAutomatic gearbox shift control.
lIdle speed control.
During engine warm up ignition timing should be an expected value of 12
° BTDC.
TestBook can not directly carry out diagnostics on the high-tension side of the ignition system. Ignition related faults
are monitored indirectly by the misfire detection system.
Input/Output
Input to the low tension side of the ignition coils comes from Fuse 14 located in the passenger compartment fuse box.
This fuse provides battery power for two ignition coils.

ENGINE MANAGEMENT SYSTEM - V8
18-2-40 DESCRIPTION AND OPERATION
Air Temperature Control (ATC) request
The ATC request comes via the ATC switch located in the facia panel. When the driver operates the switch it acts as
a request from the ATC ECU to engage the ATC clutch to drive the system.
During periods of high driver demand such as hard acceleration or maximum rev/min the ATC clutch will be disabled
for a short time. This is to reduce the load on the engine.

+ AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.
Input/Output
The operation of the ATC request is via a switch being connected to earth. Voltage is supplied via pin 38 of connector
C0637 of the ECM, at the point at when the switch is pressed the connection is made and the ATC clutch is engaged.
The ATC request can fail as follows:
lOpen circuit.
lShort circuit to voltage supply.
lShort circuit to vehicle earth.
lWiring loom fault.
In the event of an ATC request failure, the ATC system does not work.
Should a malfunction of the component occur the following fault codes may be evident and can be retrieved by
TestBook.
ATC compressor clutch relay
The ATC compressor clutch relay is located in the engine compartment fuse box. It is a four pin normally open relay.
The relay must be energised to drive the ATC compressor clutch.
P Code J2012 Description Land Rover Description
P1535 Air conditioning compressor request
malfunctionATC requested when not in standby mode

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-41
Input/Output
The ECM provides the earth for the relay coil to allow the relay contacts to close and the ATC 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 coil.
When the ECM opens the earth path, the return spring in the relay will pull the contacts apart to shut down the ATC
clutch drive.
Input to the ATC clutch relay switching contacts is via fuse 6 located in the engine compartment fuse box. The relay
coils are supplied with battery voltage from the main relay, also located in the engine compartment fuse box. The earth
path for the relay coil is via pin 29 of the ECM C0657 connector. When the relay is energised the output from the
switching contacts goes directly to the ATC compressor clutch.
The ATC clutch 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 an ATC clutch relay failure, the ATC does not work.
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
P1536 Air conditioning compressor request range/
performanceATC compressor clutch relay open circuit
P1537 Air conditioning compressor request low input ATC compressor clutch relay short to earth
P1538 Air conditioning compressor request high input ATC compressor clutch relay short to battery supply

ENGINE MANAGEMENT SYSTEM - V8
18-2-42 DESCRIPTION AND OPERATION
Cooling fan relay
The cooling fan relay is located in the engine compartment fuse box. It is a four pin normally open relay. The relay
must be energised to drive the cooling fan.
The cooling fan is used to cool both the condenser in which the ATC refrigerant is held and the radiator. This 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 fails.
Input/Output
The ECM provides the earth for the relay coils 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 opens 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 cooling fan relay switching contacts is via fuse 5 located in the engine compartment fuse box. The relay
coils are supplied with battery voltage from the main relay, also located in the engine compartment fuse box. The earth
path for the relay coils is via pin 31 of the ECM connector C0636. When the relay is energised the output from the
switching contacts is directly to the cooling fan motor.
The cooling fan relay can fail in the following ways:
lRelay open circuit.
lShort circuit to vehicle battery supply.
lShort circuit to vehicle earth.
lBroken return spring.
In the event of a cooling fan relay failure, the cooling fan does not work.

FUEL DELIVERY SYSTEM - TD5
DESCRIPTION AND OPERATION 19-1-5
The fuel pump is a 'self priming', wet type, two stage pump which is immersed in fuel in the tank and operates at all
times when the ignition switch is in position II. If the engine is not started, the ECU will 'time-out' after three minutes
and de-energise the fuel pump relay. The pump receives a feed from the battery via fuse 10 in the engine
compartment fusebox and the fuel pump relay. The relay is energised by the ECM when the ignition switch is moved
to position II.
The fuel pump assembly is retained with a locking ring and sealed with a rubber seal. The locking ring requires a
special tool for removal and refitment. An access panel for the fuel pump is located in the loadspace floor below the
carpet. The access panel is sealed to the floor with a rubber seal and retained by six self-tapping screws. A four pin
electrical connector is located on the top cover and provides power feed and earth for the fuel pump and also inputs
and outputs for the fuel gauge sender operation.
The fuel gauge sender is integral with the fuel pump. The sender is submerged in the fuel and is operated by a float
which moves with the fuel level in the tank.
Fuel pump
The fuel pump assembly comprises a top cover which locates the electrical connector, fuel burning heater connection
and four fuel pipe couplings. The top cover is attached to a plastic cup shaped housing and retained on three sliding
clips. Two coil springs are located between the cover and the housing and ensure that the fuel pump remains seated
positively at the bottom of the tank when installed.
The housing locates the two stage fuel pump and also the fuel gauge sender unit. The lower part of the housing is the
swirl pot which maintains a constant level of fuel at the fuel pick-up. A coarse filter is located in the base of the housing
and prevents the ingress of contaminants into the pump and the fuel system from the fuel being drawn into the pump.
A fine filter is located in the intake to the low pressure stage to protect the pump from contaminants. Flexible pipes
connect the couplings on the top cover to the pump.
A non-return valve is located in the base of the housing. When the fuel tank is full, fuel pressure keeps the valve lifted
from its seat allowing fuel to flow into the swirl pot. As the tank level reduces, the fuel pressure in the tank reduces
causing the valve to close. When the valve is closed fuel is retained in the swirl pot, ensuring that the swirl pot remains
full and maintains a constant supply to the fuel pump.
The two stage pump comprises a high and a low pressure stage. The low pressure stage draws fuel from the swirl
pot through the filter. The low pressure stage pumps fluid at a pressure of 0.75 bar (10.9 lbf.in
2) and a flow of 30 litres/
hour (8 US Gallons/hour) to the fuel filter. A proportion of the fuel from the low pressure stage also passes, via a
restrictor, through a jet pump which keeps fuel circulating in the swirl pot. The high pressure stage draws the low
pressure fuel from the fuel filter and pressurises it to a pressure of 4.0 bar (58 lbf.in
2). The pressurised fuel is then
passed from the pump to the injectors at a flow of 180 litres/hour (47.6 US Gallons/hour). A fuel pressure regulator is
located at the rear of the engine and ensures that the delivery pressure remains at 4.0 bar (58 lbf.in
2) by controlling
the amount of fuel returning to the fuel tank.
The fuel pump has a maximum current draw of 15 Amps at 12.5 V and is protected by a 20 Amp fuse in the engine
compartment fusebox.