Land Rover Defender Electrical Library 3rd Edition Nas Rover Manual

							CIRCUIT OPERATION
DEFENDER 90 NAS5The ECM determines the optimum ignition timing based on signals from the following
sensors: 
· Crankshaft position (CKP) sensor - engine speed and crankshaft position 
· Camshaft position (CMP) sensor - camshaft position 
· Intake air temperature (IAT) sensor - inlet air temperature 
· Knock sensors - engine vibration, detonation  
The engine management system uses no centrifugal or vacuum advance, timing is
controlled entirely by the ECM.  
Crankshaft position (CKP) sensor  
The CKP sensor signal is used as the basis for ignition timing.  It informs the ECM that
the engine is turning, the speed the engine is turning and position of the engine in its
cycle.  
The sensor uses the principle of magnetic induction to generate the signal. A reluctor ring,
attached to the engine flywheel, has a series of teeth spaced at 10°  intervals, with one
tooth missing at 20°  after TDC.  The reluctor ring rotates with the engine, in close
proximity to the CKP sensor. As each tooth of the reluctor ring passes the sensor, it
disturbs the magnetic field of the sensor and a voltage is induced in the sensor coil.  The
ECM calculates engine speed by counting pulses per second from the CKP sensor.
Engine position is calculated by counting pulses after missing pulse. 
In the event of a sensor failure, the engine will not run.
Camshaft position (CMP) sensor  
The CMP sensor is used in conjunction with the CKP sensor to inform the ECM of the
position of the engine in the 4 stroke cycle.  Using the CKP sensor alone, the ECM is
unable to determine whether a cylinder is on its compression stroke or exhaust stroke.    
The sensor uses the principle of magnetic induction to generate the signal.  The cam
wheel has four lobes which pass in close proximity to the CMP sensor as the camshaft
rotates.  The lobes disturb the magnetic field of the sensor and induce a voltage in the
sensor coil.  
In the event of a sensor failure, the ECM will continue to operate normal ignition timing
using the CKP sensor signal. Engine knock detection and correction will be disabled.   
						

							CIRCUIT OPERATION
6DEFENDER 90 NASInlet air temperature (IAT) sensor  
The basis of the IAT sensor is a temperature dependent resistive metal strip.  The
resistance of the metal strip varies considerably with temperature.  When an inlet
temperature of 55 °C or higher is detected, the ECM retards the ignition timing .  If the
sensor fails, the ECM assumes an inlet temperature of 50 °C.   
Knock sensor  
The knock sensor is a piezo-electronic accelerometer, which produces an electronic signal
related to the vibration of the engine.  A knock sensor is located in each bank of
cylinders.  The signal from each knock sensor is transmitted to the ECM.  The ECM is
able to filter out normal engine vibrations and detect vibrations induced by engine
knock.  
Using the signal from the knock sensor in conjunction with the CKP and CMP signals
enables the ECM to identify which cylinder is producing the knock and hence retard the
ignition timing of that cylinder only.  The ignition timing of the cylinder producing the
knock is retarded until the knock disappears. The ECM then advances the ignition timing
to find the optimum advance angle for that cylinder.  The ECM is able to perform a
similar function for each of the 8 cylinders simultaneously.  It is therefore possible for all
8 cylinders to have different advance angles at any one time.  
FUELLING SYSTEM  
Engine fuelling is by a fully sequential, electronic fuel injection system, controlled by the
ECM. The ECM determines the timing and quantity of fuel to be injected based on
information received from the following sensors.  
· Crankshaft position (CKP) sensor - engine speed and crankshaft position 
· Camshaft position (CMP) sensor - camshaft position 
· Mass air flow (MAF) sensor - quantity of air entering the engine 
· Intake air temperature (IAT) sensor - temperature and hence density of air entering
the engine
· Throttle position (TP) sensor - position of throttle and rate of change of throttle 
· Engine coolant temperature (ECT) sensor - coolant temperature 
· Engine fuel temperature (EFT) sensor - temperature of fuel rail 
· Heated oxygen sensor (HO2S) - oxygen content of exhaust   
						

							CIRCUIT OPERATION
DEFENDER 90 NAS7Crankshaft position (CKP) sensor   
The CKP sensor signal is used as the basis for fuel injection timing.  It informs the GEMS
that the engine is turning, the speed at which it is turning and its position in the 4 stroke
cycle.  
The sensor uses the principle of magnetic induction to generate the signal. A reluctor ring,
attached to the engine flywheel, has a series of teeth spaced at 10 °  intervals, with one
tooth missing at 20 °  after TDC.  The reluctor ring rotates with the engine, in close
proximity to the CKP sensor. As each tooth of the reluctor ring passes the sensor, it
disturbs the magnetic field of the sensor and a voltage is induced in the sensor coil.  The
ECM calculates engine speed by counting pulses per second from the CKP sensor.
Engine position is calculated by counting pulses after missing pulse.  
Camshaft position (CMP) sensor  
The CMP sensor is used in conjunction with the CKP sensor to inform the ECM of the
position of the engine in the 4 stroke cycle.  Using the CKP sensor alone, the ECM is
unable to determine whether a cylinder is on compression stroke or exhaust stroke.    
The sensor uses the principle of magnetic induction to generate the signal.  The cam
wheel has four lobes which pass in close proximity to the CMP sensor as the camshaft
rotates.  The lobes disturb the magnetic field of the sensor and induce a voltage in the
sensor coil.  
In the event of a sensor failure, the ECM will continue to operate sequential fuel injection
using the CKP sensor signal.  It is possible that the injection timing will be one engine
revolution out of sequence.  
Mass air flow (MAF) sensor  
The MAF sensor is used to measure the quantity of air being drawn into the engine and
hence give an indication of the quantity of fuel to be injected to provide a stoichiometric
(chemically correct ratio) mixture strength.  
The MAF sensor is an anemometer located in the inlet air flow, upstream of the throttle
body, which uses the Hot Wire principle to determine air flow. A single metering wire is
maintained at a constant temperature. As  air flows over the wire, current is applied to the
wire to maintain the temperature at its reference temperature, the faster the air flow, the
greater the cooling effect and the greater the current required to maintain the temperature.
The current supplied to the hot wire is converted to a voltage signal and sent to the ECM.
The ECM uses the voltage signal to calculate the quantity of air being drawn into the
engine.  If the sensor fails, the ECM calculates a value dependent on throttle position,
engine speed and air temperature.   
						

							CIRCUIT OPERATION
8DEFENDER 90 NASIntake air temperature (IAT) sensor
The IAT sensor, by measuring the temperature of induction air, enables the ECM to
determine the density, and hence, the oxygen content of the air being burned in the
engine. As air temperature increases, it expands, and its density (Mass/Unit of Volume)
decreases. The basis of the IAT sensor is a temperature dependent resistive metal strip.
The resistance of the metal strip varies considerably with temperature.  When an inlet
temperature of 55 °C or higher is detected, the ECM retards the ignition timing .  If the
sensor fails, the ECM assumes an inlet temperature of 50 °C.   
Throttle position (TP) sensor  
The TP sensor measures the angle of throttle opening and the rate of change of throttle
position. The angle of throttle opening gives an indication of the quantity of air being
drawn into the engine. The rate of change of throttle angle gives an indication of rate of
acceleration demanded.  
The sensor is a rotary variable resistor mounted to the throttle butterfly spindle giving an
output of 0 to 5 volts.  
Engine coolant temperature (ECT) sensor  
The coolant temperature sensor measures the temperature of the engine coolant fluid. The
signal from the coolant sensor is used by the ECM to adjust the fuelling mixture. The
engine requires a richer mixture at lower temperatures.  
The sensor relies on a temperature dependent resistive metal strip.  The resistance of the
metal strip varies considerably with temperature and is immersed in the engine coolant
fluid.  
If the sensor fails, the ECM assumes and engine coolant figure of 80°C. The fault could
be noticeable during the engine warm up period.  
Engine Fuel Temperature (EFT) sensor  
The fuel temperature sensor measures the temperature of the fuel rail. The signal from the
sensor gives the ECM a warning of fuel vaporization and the possibility of bubbles
forming in the injectors, which may cause poor hot starting. If the ECM receives a high
fuel temperature signal during starting, the fuel injector opening period is increased to
clear any vaporization bubbles from the injectors and correct the fuelling.  When the
engine is running, fuel circulation from the fuel tank keeps the fuel rail cool. 
						

							CIRCUIT OPERATION
DEFENDER 90 NAS9Heated oxygen sensor (HO2S)  
4 HO2Ss are fitted to the vehicle, one before and one after each catalyst.  The HO2S
comprises a titanium metal sensor surrounded by a gas permeable ceramic coating.
Oxygen permeating the ceramic coating reacts with the titanium wire, altering its
resistance.  The resistance of the sensor is directly related to the quantity of oxygen
around the sensor.  The HO2S does not function correctly until it reaches a temperature of
approximately 300°C and so a heating element is incorporated into the sensor to provide
rapid warm up after a cold start.   
The signals from the HO2Ss are used by the ECM to correct the fuelling to each bank of
cylinders independently.  The 2 sensors upstream of the catalysts measure the oxygen
content of the gasses exhausted from the engine, indicating a rich or weak mixture
strength. The ECM alters the pulse width of the injectors to correct the mixture strength
and achieve a stoichiometric air/fuel ratio.  The 2 HO2Ss downstream of the catalysts
measure the efficiency of the catalysts by comparing the sensors voltage switching
frequency to that of the upstream catalysts. If the catalyst is operating efficiently, the
switching frequency of the downstream sensor will be lower than that of the upstream
sensor.   
Injectors  
The fuel injection system has 8 fuel injectors, 1 for each cylinder.  Each injector
comprises  a solenoid with a needle valve held in position by a spring.  The route to
ground for the solenoid is controlled by the ECM. When energized, the solenoid lifts the
needle valve from its seat and pressurized fuel from the fuel rail flows through the
injector. The ECM controls the amount of fuel delivered by opening the injector for
varying periods. The injector orifice is shaped to produce a fine spray of fuel which aids
combustion.  
Fuel pressure regulator  
The fuel pressure regulator is a mechanical device mounted to the fuel rail.  Its purpose is
to control the fuel rail pressure at a fixed level above inlet manifold depression, thus
ensuring that the correct amount of fuel is injected for given injector opening times.
The fuel pressure regulator contains a spring loaded diaphragm valve with pressurized
fuel on one side of the diaphragm and manifold depression acting on the other.  When fuel
rail pressure, assisted by manifold depression, overcomes the diaphragm spring load , fuel
flows past the diaphragm valve to the fuel tank, reducing fuel rail pressure.  With
manifold depression low, during hard acceleration, the fuel rail pressure must be high to
overcome the diaphragm spring load.  With manifold depression low, during coast down,
the vacuum acting on the diaphragm valve acts against the spring load and a lower fuel
rail pressure lifts the valve from its seat.   
						

							CIRCUIT OPERATION
10DEFENDER 90 NASIdle air control valve  (IACV)  
Engine idle speed is maintained by the IACV, controlled by the ECM.  With the throttle
butterfly fully closed, a small quantity of air is able to by-pass the throttle butterfly via the
base idle passage.  The ECM  monitors engine speed and load via sensors around the
engine. Should extra air be required to maintain a steady idle speed, the ECM signals the
IACV to operate a number of steps and open the throttle by-pass. The stepper motor,
integral to the IACV, operates over a range of 200 steps with the valve fully open at 200
steps and fully closed at 0 steps.   
Canister purge valve (CANPV) 
The vehicle is equipped with an evaporative emission control system designed to prevent
vapor loss from the fuel tank.  Fuel tank vapor is passed through a charcoal canister
which traps fuel vapor. The vapor trapped by the charcoal canister is drawn in to the
engine through the purge valve and burnt in the combustion chamber.  
The ECM controls the opening of the CANPV to allow venting of the charcoal canister.
The ECM pulses the valve open for short periods when the engine has reached normal
operating temperature and is turning at a speed over 1700 rpm. This is done to ensure that
the fuelling of the engine is not adversely affected during warm up or at idle. During
purge valve operation, the ECM monitors HO2S signals.  If opening the purge valve
causes the HO2S signal to indicate a leaner mixture, the ECM assumes that the charcoal
canister is empty. When the ECM senses that the charcoal canister is empty, the purge
valve is opened to prevent a build up of fuel vapor in the canister. With the purge valve
open, unmetered air is drawn into the engine through the charcoal canister. The ECM
uses the signal from the HO2Ss to correct the fuelling.  
						

							CIRCUIT OPERATION
DEFENDER 90 NAS11 
OTHER FEATURES
Rough road detection ECU  
When running on rough roads, it is possible for a false indication of engine misfire to be
detected by the ECM. To prevent false fault codes being stored in the ECM, a rough road
detection ECU is fitted to the vehicle. When the rough road detection ECU signals rough
road conditions, the ECM temporarily ignores engine misfire signals.  
The rough road detection ECU monitors and compares the speed of all 4 wheels. When
the vehicle is traveling on rough roads, the wheels will rotate at varying speeds as
obstacles are negotiated and wheel slippage occurs.  The variance in wheel speeds is
detected by the ECU which signals rough road conditions to the ECM.  
Inertia switch  
Power to the fuel pump is supplied via the inertia switch. In the event of extreme
deceleration, as would be experienced in a collision, the inertia switch trips, isolating
electrical supply from the fuel pump.  The switch is reset by pressing the rubber button on
top of the switch.   
						

							CIRCUIT OPERATION
12DEFENDER 90 NASSEAT BELT WARNING  
DESCRIPTION  
If the ignition is switched on without the seat belt being fastened, a warning light will be
illuminated on the instrument pack and an audible warning will sound.  
OPERATION  
Feed from the positive battery terminal is connected to the engine compartment fuse box
(C632-1) by the brown wire.  Current passes through fusible link 1 and fusible link 5 of
the engine compartment fuse box which are connected in series. Fusible link 5 (C570-2)
is connected to the ignition switch  (C28-1) by the brown wire.  
With the ignition switch in position II, power flows through the ignition switch (C94-1)
to fuse 1 of the passenger compartment fuse box (C580-1) on the white wire.  Fuse 1
(C580-2) supplies the multi-function ECU sounder (C16-5) and instrument pack seat belt
warning light (C230-4) on white/green wires.  The ECU (62-7) and warning light (C230-
1) are connected to the seat belt buckle switch (C100-2) by white/black wires.  With the
seat belt unfastened, the switch is closed and provides a route to ground (C100-1) for the
sounder and warning light on the black wire.  Fastening the seat belt opens the switch and
breaks the circuit, extinguishing the warning light and silencing the sounder.  
						

							CIRCUIT OPERATION
DEFENDER 90 NAS13AIR CONDITIONING
BLOWER OPERATION
With the ignition in position 2, a battery feed passes from the ignition switch (C94-1) to
Fuse 17 (C581-13) on a white wire. Fuse 17 (C581-14) provides a feed to the Blower
Relay coil (C55-4) on a green wire. The coil is grounded on a black wire and the relay is
energized whenever the ignition switch is at position II.
With the relay energized, a battery feed from Fuse 15 (C581-10) on a purple and slate
wire passes through the closed relay contacts (C55-1 & 3) to the blower switch (C102-5)
on a brown wire.
When the Blower Motor Switch is turned to position 1 (C102-1), the blower motor (C52-
1) is fed on a blue wire. Current passes through both blower motor resistors and the
blower operates at slow speed.
When the Blower Motor Switch is turned to position 2 (C102-2), the blower motor (C64-
1) is fed on a green wire. Current now passes through only one resistor, so the motor
operates at intermediate speed.
With the Blower Motor Switch in position 3 (C102-3), the blower motor (C65-1) is fed
on a red wire. Current flows directly to the motor winding and the motor operates at fast
speed.
The Blower Motor is grounded on a black wire in all switch positions.
AIR CONDITIONING REQUEST
Operation of the air conditioning system is controlled by the Generic Engine Management
System (GEMS) Engine Control Module (ECM). The ECM will decide whether to
operate the Air Conditioning Compressor Clutch on receipt of an air conditioning request
signal. The request signal takes the form of a ground signal applied to pin 28 of ECM
connector C636. The signal is dependent on the following:
· A pressure of not greater than 30 Bar (435 psi) and not less than 2.4 Bar (35 psi) must
exist at the high pressure and low pressure switch contacts within the Trinary Switch
(C51-1 & C51-2).
· The Air Conditioning Thermostat Switch must be closed. The switch will be closed
whenever its probe, positioned in the vanes of the evaporator, senses a warmer
temperature than that set at the switch.
· The logic relay must be energized. The relay is energized with a feed on the blue and
yellow wire from the blower switch (C102-4) whenever the Blower Motor is operating.
The relay coil is grounded on a black wire. 
						

							CIRCUIT OPERATION
14DEFENDER 90 NASWhen all of the above conditions are met, the ground path for the air conditioning request
signal is completed. The ECM then registers receipt of the request signal and will issue an
Air Conditioning Grant Signal when the necessary changes have been made to idle speed.
Similarly, when the Air Conditioning Request signal is removed, the ECM will delay
disengagement of the compressor clutch until the correct conditions are met. The purpose
of this Request/Grant process is to ensure that idle speed remains as near constant as
possible during engagement & disengagement of the compressor clutch.
AIR CONDITIONING GRANT
When the GEMS ECM decides that the necessary conditions have been met to allow
engagement of the Air Conditioning (A/C) Compressor Clutch, and hence, grant operation
of the air conditioning system, it applies a ground (C634-1) on the black and slate wire.
At the A/C harness connector (C47-4), the wire color changes to blue and black, where it
continues to the Air Conditioning Compressor Clutch Relay (C60-2). The relay coil (C60-
4) is fed from fuse 17 (C581-14) on a green wire when the Ignition Switch is at position
II.
With the clutch relay energized, a battery feed from Fuse 16 (C581-12) passes to the
compressor clutch relay (C60-1) on a brown and white wire. The feed passes to the
compressor clutch (C49-1) through the closed relay contacts (C60-3) on a brown and pink
wire. The compressor clutch is grounded on a black wire.
High Temperature Disable
The ECM can disable compressor clutch operation to reduce engine load during high
engine temperatures. The purpose of this system is to prevent engine overheat.
When the ECM senses a high coolant temperature (above 112 
deg C - 234 deg F) via the
Engine Coolant Temperature (ECT) sensor (C636-14), Air Conditioning Grant is
overridden by removing the ground signal from C634-1. The Air Conditioning
Compressor Clutch Relay is then de-energized, disabling the Air Conditioning
Compressor Clutch. This condition will remain until coolant temperature drops to
acceptable levels.
CONDENSER FAN REQUEST
Operation of the condenser fan is controlled by the GEMS ECM using a Request/Grant
process, similar to that used in Air Conditioning Compressor Clutch circuit. The request
signal is received as a ground applied to the ECM (C636-29) through the medium
pressure switch contacts in the Trinary Switch (C51-3 & C51-4). The Trinary Switch
medium pressure contacts close at pressures greater than 21 Bar (305 psi) and reopen
when pressure falls below 17 Bar (247 psi).