Defender (1999-2002). Manual - part 52

ENGINE MANAGEMENT SYSTEM

DESCRIPTION AND OPERATION

SENSOR - MANIFOLD ABSOLUTE PRESSURE
(MAP) / INLET AIR TEMPERATURE (IAT)

The MAP/IAT sensors are combined in one unit located in the inlet manifold. It provides pressure and temperature
information about the air in the inlet manifold to the ECM. The ECM compares the voltage signal to stored values
and compensates fuel delivery as necessary. The ECM uses the signal from the MAP/IAT sensor for the following
functions:

•

To calculate the delivered fuel limits.

•

To calculate the air mass in the cylinder.

•

To calculate the air speed density.

•

To calculate the air temperature.

The MAP sensor works on the piezo crystal principal. Piezo crystals are pressure sensitive and will oscillate in
accordance to changes in air pressure. The MAP sensor produces a voltage between 0 and 5 volts proportional to
the pressure level of the air in the inlet manifold. A reading of 0 volts indicates a low pressure, a reading of 5 volts
a high pressure.

The IAT portion of the sensor works as a Negative Temperature Co-efficient (NTC) sensor. As air temperature
rises, the resistance in the sensor decreases. As temperature decreases the resistance in the sensor increases.
The ECM compares the voltage signal to stored values and compensates fuel delivery as necessary.

Inputs / Outputs
The MAP/IAT sensor (C0567-3) is provided a 5 volt supply by the ECM (C0158-8) on a pink/purple wire. The
MAP/IAT sensor provides the ECM with 2 outputs. The MAP sensor output (C0567-4) is connected to the ECM
(C0158-6) by a white/yellow wire. The IAT sensor output (C0567-2) is connected to the ECM (C0158-34) on a
green/black wire. The MAP/IAT sensor is earthed (C0567-1) via the ECM (C0158-17) on a pink/black wire.

ENGINE MANAGEMENT SYSTEM

DESCRIPTION AND OPERATION

The MAP/IAT sensor can fail, or supply an incorrect signal if one or more of the following occur:

•

Sensor open circuit.

•

Short circuit to vehicle supply.

•

Short circuit to vehicle earth.

•

Contaminated sensor element.

•

Damaged sensor element.

•

Resistance in wiring harness.

In the event of a MAP/IAT sensor failure any of the following symptoms may be observed:

•

If the MAP sensor fails manifold pressure is set to a pre-determined default value and the engine performance
will be reduced.

•

If the IAT sensor fails the ECM will set air temperature to a fixed value. The ECM will use a fixed default value
from its memory.

ENGINE MANAGEMENT SYSTEM

DESCRIPTION AND OPERATION

SENSOR - ENGINE COOLANT TEMPERATURE
(ECT)

The ECT sensor is located in the coolant outlet elbow on top of the engine. It provides the ECM with engine
coolant temperature information. The ECM uses this information for the following functions:

•

Fuelling calculations.

•

Temperature gauge.

•

To limit engine operation if coolant temperature is to high.

•

Cooling fan operation.

•

Glow plug operating time.

The ECT works as an NTC sensor. As temperature rises, the resistance in the sensor decreases, as temperature
decreases, the resistance in the sensor increases. The ECM compares the voltage signal to stored values and
compensates fuel delivery to ensure optimum driveability at all times.

Inputs / Outputs
The ECT sensor (C0169-2) is provided a feed by the ECM (C0158-7) on a pink/green wire. The sensor is provided
an earth path (C0169-1) via the ECM (C0158-18) on a pink/black wire.

The ECT can fail or supply an incorrect signal if one or more of the following occurs:

•

Sensor open circuit.

•

Short circuit to vehicle supply.

•

Short circuit to vehicle earth.

•

Incorrect mechanical fitting.

•

Signal fixed above 40

C (104

F) not detected.

•

Signal fixed below 40

C (104

F) not detected.

In the event of an ECT sensor failure, any of the following symptoms may be observed:

•

Difficult cold start.

•

Difficult hot start.

•

Driveability concerns.

•

Instrument pack warning lamp illuminated.

•

Temperature gauge reads excessively hot.

•

Temperature gauge reads excessively cold.

In the event of a component failure the ECM calculates coolant temperature from the fuel temperature signal. If
this occurs, the limit of engine operation if coolant temperature becomes too high becomes inoperative.

ENGINE MANAGEMENT SYSTEM

DESCRIPTION AND OPERATION

SENSOR - CRANKSHAFT SPEED AND
POSITION (CKP)

The CKP sensor is located in the transmission housing with its tip adjacent to the outer circumference of the
flywheel. The CKP sensor works on the variable reluctance principal, which sends a signal back to the ECM in the
form of an ac voltage.

The ECM uses the signal from the CKP sensor for the following functions.

•

To calculate engine speed.

•

To determine engine crank position.

•

To determine fuel injection timing.

The CKP sensor works as a Variable Reluctance Sensor (VRS). It uses an electromagnet and a target ring to
generate a signal. As the target ring passes the tip of the CKP sensor the magnetic field produced by the sensor is
cut and then re-instated. The ECM measures the signal as an ac voltage.

The outer circumference of the flywheel acts as the target ring for the sensor. The flywheel is divided into 36
segments, each of 10

. 31 segments have drilled holes and 5 segments are spaces. This equals 360

or one

engine revolution. The 5 spaces correspond to the TDC position of the 5 cylinders. This allows the ECM to control
fuel injection timing for each of the cylinders.

Inputs / Outputs
The two pins of the CKP sensor (C1068-1 & C1068-2) are both outputs. The ECM (C0158-13 & C0158-36)
processes the outputs of the sensor. To protect the integrity of the CKP sensor signal, an earth screen is used.

The ECM measures the outputs from the CKP sensor. The ECM (C0158-13) measures a positive signal on a
pink/black wire, and a negative signal (C0158-36) on a white/blue wire. The earth path for the sensor is via the
ECM (C0158-16).

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