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Discovery 2. Manual - part 74

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-25

In the event of a MAF sensor signal failure any of the following symptoms may be observed:

During driving engine rev/min may dip, before recovering.

Difficult starting.

Engine stalls after starting.

Delayed throttle response.

Emissions control inoperative.

Idle speed control inoperative.

Reduced engine performance.

MAF sensor signal offset.

There are two types of MAF sensor diagnostic check:

The MAF sensor signal is less than the minimum threshold for specific speed range – the engine must have
exceeded 200 rev/min for longer than 300 ms and remain above 400 rev/min. The signal must be less than the
threshold mapped against engine speed for longer than 500 ms.

The MAF sensor signal is greater than the maximum threshold for specific speed range – the engine must have
exceeded 200 rev/min for longer than 10 ms. The signal must be greater than the threshold mapped against
engine speed for longer than 300 ms.

If the MAF sensor fails the following fault codes will be produced and can be retrieved by TestBook:

P code

J2012 description

Land Rover description

P0102

Mass or volume air flow low input

MAF signal < minimum threshold, which is speed
dependent

P0103

Mass or volume air flow circuit high input

MAF signal > maximum threshold, which is speed
dependent

ENGINE MANAGEMENT SYSTEM - V8

18-2-26 DESCRIPTION AND OPERATION

Intake air temperature (IAT) sensor
The intake air temperature (IAT) sensor utilises a thermistor with a negative temperature coefficient (NTC); as
temperature rises, the thermistor resistance decreases. The change in resistance causes a change in input voltage
at the ECM. The ECM converts the voltage value it receives to provide an indication of the temperature of the inlet air.

Normal operating parameters of the IAT sensor are as follows:

IAT output

Should the IAT sensor fail, the ECM defaults to an assumed air temperature of 45

C (113

F).

The IAT sensor can fail the following ways or supply incorrect signal:

Sensor open circuit.

Short circuit to vehicle battery supply.

Short circuit to vehicle earth.

Increased sensor resistance.

Damaged sensor element.

In the event of an IAT sensor signal failure any of the following symptoms may be observed:

Adaptive fuelling disabled.

Idle speed adaption disabled.

Catalyst monitoring affected due to exhaust temperature model.

Idle speed actuator test disabled.

Warm up ignition angle affected.

Condenser fan hot restart inhibited.

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-27

There are two types of IAT sensor diagnostic checks:

The IAT sensor signal is less than the minimum threshold – the engine has to have been running for longer than
180 seconds, and idle speed control must have been operational for longer than 10 seconds. No fuel cut off is
active. The IAT sensor signal must be less than -35

C (-31

F) for longer than 200 ms.

The IAT sensor signal is greater than the maximum threshold – the ECM has to be powered up (engine does not
need to be running), and the signal must be greater than 140

C (284

F) for longer than 200 ms.

If the IAT sensor fails the following fault codes will be produced and can be retrieved by TestBook:

Air intake duct – Gulf models from 2000MY

1 Heat reflective insulation

2 Supplementary air intake duct

The density of the intake air is partly dependent on altitude and temperature. Hot air has a lower density than cold air;
consequently in hot climates, the low air density can result in low power due to low volumetric efficiency.

In order to improve engine performance, Gulf specification models from 2000MY have a secondary air intake duct
which is located under the front left inner wing of the vehicle. Cooler air from the side of the vehicle is routed through
the duct to the air cleaner, where it combines with air entering via the front grille.

In addition to the secondary air duct, the vehicles are fitted with a larger front grille and have larger cooling and
condenser fans.

The MAF/IAT sensor, air cleaner and air cleaner duct are encased in insulation bags to help keep the intake air cool
and so increase the mass of air entering the engine intake manifold.

The air cleaner includes a cyclone filter and also a dump valve in the bottom of the unit. Sand and dust particles which
are carried into the air cleaner with the air flow are automatically expunged via the dump valve.

P code

J2012 description

Land Rover description

P0112

Intake air temperature circuit low input

Intake air temperature signal less than minimum
threshold, after time for exhaust to warm up

P0113

Intake air temperature circuit high input

Intake air temperature signal greater than maximum
threshold

M180452

ENGINE MANAGEMENT SYSTEM - V8

18-2-28 DESCRIPTION AND OPERATION

Throttle Position (TP) sensor (C0175)

The TP sensor is located on the throttle body assembly in the engine compartment. The ECM is able to determine the
position of the throttle plate and the rate of change of its angle. The ECM processes the signal received from the TP
sensor.

The TP sensor consists of a resistance track and a sliding contact connected to the throttle plate assembly. As the
throttle is opened and closed the sliding contact moves along the resistance track to change the output voltage of the
sensor. The ECM determines throttle plate position by processing this output voltage. The connection of the sensor
to the throttle plate assembly is via a shaft.

The ECM is able to determine the closed throttle position, this enables the TP sensor to be fitted without the need for
prior adjustment. The TP sensor signal has input into the ECM's fuelling strategy and also to determine closed throttle
position for idle speed control. The TP sensor also supplies the ECM with information to enable the overrun fuel cut
off strategy to be implemented. When the ECM receives closed throttle information from the TP sensor it closes the
injectors for the duration of the closed throttle time.

The TP sensor signal is also used by the Electronic Automatic Transmission (EAT) ECU to determine the correct point
for gear shifts and acceleration kickdown. The ECM also supplies the SLABS ECU with this TP sensor information as
a PWM signal.

Input/Output
The TP sensor has electrical input and output. Input is a 5 volt supply via pin 10 of connector C0636 of the ECM. The
signal output is via pin 24 of connector C0636 and is a varying voltage, less than 0.5V (closed throttle) and greater
than 4.5V (wide open throttle) depending on throttle plate position. The TP sensor earth is via pin 25 of connector
C0636 of the ECM, this acts as a screen to protect the integrity of the TP sensor signal.

The connector and sensor terminals are gold plated for corrosion and temperature resistance, care must be exercised
while probing the connector and sensor terminals.

If the TP sensor signal fails, the ECM uses a default value derived from engine load and speed.

The TP sensor can fail the following ways or supply incorrect signal:

Sensor open circuit.

Short circuit to vehicle supply.

Short circuit to vehicle earth.

Signal out of parameters.

Blocked air filter (load monitoring, ratio of the TP sensor to air flow).

Restriction in air inlet (load monitoring, ratio of the TP sensor to air flow).

Vacuum leak

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