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)...

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...

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...

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...

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...

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...

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...

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...

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...

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...