LAND ROVER DEFENDER 1999 Workshop Manual

18ENGINE MANAGEMENT SYSTEM
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DESCRIPTION AND OPERATION SENSOR - AMBIENT AIR PRESSURE AND
TEMPERATURE (AAP)
The AAP sensor is located in the top of the air filter housing. It provides a voltage signal relative to ambient air
pressure to the ECM. The AAP sensor works on the piezo crystal principal. Piezo crystals are pressure sensitive
and will oscillate in accordance to changes in air pressure. The AAP sensor produces a voltage between 0 and 5
volts proportional to the pressure level of the air in the air filter housing. A reading of 0 volts indicates low pressure
and a reading of 5 volts a high pressure. The ECM uses this signal for the following functions.
To maintain manifold boost pressure.
To reduce exhaust smoke emissions while driving at high altitudes.
Control of the EGR system.
Inputs / Outputs
The ECM (C0158-8) supplies the AAP sensor (C0188-3) with a 5 volt feed on a pink/purple wire. The output signal
from the AAP sensor (C0188-2) is sent to the ECM (C0158-10) on a white/yellow wire. The AAP sensor is earthed
(C0188-1) via the ECM (C0158-30) on a pink/black wire.
The AAP sensor 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.
Contaminated sensor element.
Damaged sensor element.
Resistance in wiring harness.
In the event of an AAP sensor signal failure, any of the following symptoms may be observed:
Altitude compensation inoperative (engine will produce black smoke).
Active boost control inoperative.
Turbocharger boost pressure limited to 1 bar (14.5 lbf.in
2).
EGR altitude compensation inoperative.
In the event of a AAP sensor failure, the ECM will use a fixed default value from its memory.
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ENGINE MANAGEMENT SYSTEM
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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.
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18ENGINE MANAGEMENT SYSTEM
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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.
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ENGINE MANAGEMENT SYSTEM
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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.
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18ENGINE MANAGEMENT SYSTEM
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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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ENGINE MANAGEMENT SYSTEM
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DESCRIPTION AND OPERATION Voltage generation from the CKP sensor is relative to engine speed. The values from a good CKP sensor are as
follows:
2 to 3 volts with engine cranking.
Rising to 6 to 6.5 volts from 1000 rev/min upwards.
The above readings are dependent upon the correct air gap between the tip of the CKP sensor and the passing
teeth of the reluctor ring.
The CKP sensor can fail or supply an incorrect signal if one or more of the following occurs:
Sensor assembly loose.
Incorrect spacer fitted.
Sensor open circuit.
Sensor short circuit.
Incorrect fitting and integrity of the sensor.
Water ingress.
In the event of a CKP sensor signal failure, any of the following symptoms may be observed:
Engine cranks but fails to start.
Engine misfires (CKP sensor incorrectly fitted).
Engine runs roughly or stalls (CKP sensor incorrectly fitted).
The CKP sensor does not have a back-up strategy. If it fails the engine will stop running and fail to start.
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18ENGINE MANAGEMENT SYSTEM
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DESCRIPTION AND OPERATION SENSOR - THROTTLE POSITION (TP)
UP TO VIN 607224
The TP sensor is located on the throttle pedal assembly. It detects throttle pedal movement and position. It uses
two position sensors to provide the ECM with the exact throttle pedal position. As the pedal operates, the voltage
of one position sensor increases as the other decreases.
Input / Output
The ECM (C0658-14) provides a 5 volt reference feed to both sensors (C0787-B & C0787-J) on white/purple wires
via header 291. The signal output from sensor 1 (C0787-F) is connected to the ECM (C0658-12) by a white/green
wire. Signal output from sensor 2 (C787-K) is connected to the ECM (C0658-36) by a white/slate wire. An earth
path is provided for both sensors (C0787-B & C0787-G) on black/yellow wires via the ECM (C0658-26)
The TP sensor 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.
Water ingress.
Sensor incorrectly fitted.
In the event of a TP sensor signal failure, any of the following symptoms may be observed:
Engine performance concern.
Delayed throttle response.
Failure of emission control.
If the TP sensor fails, the engine will only run at idle speed until the fault is eliminated.
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ENGINE MANAGEMENT SYSTEM
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DESCRIPTION AND OPERATION SENSOR - THROTTLE POSITION (TP)
FROM VIN 607225
Defender vehicles from VIN 607225 use three track thick film potentiometers. No idle speed sender switch is used
on this type of sensor because the ECM can compare the two or three sets of signals to implement idle speed
control and over-run fuel shut-off. The two potentiometers are known as track 1 and 2 potentiometers. The track 3
potentiometer on later models is used to improve the resolution of the pedal. The ECM provides a 5V supply and
receives a signal from each of the potentiometer tracks.
Td5 TP Sensor Signal Output
A = Track 1
B = Track 2
C = Track 3
D = Voltage
E = Pedal Angle (Degrees)
F = Not applicable for Defender
G = Wide open throttle stop tolerance band
With reference to the above graph, at idle (throttle released), track 2 returns a signal of 4.2V to the ECM and track
1 returns a signal of 0.8V. The ECM calculates the sum of these two figures which totals 5.0V.
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18ENGINE MANAGEMENT SYSTEM
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DESCRIPTION AND OPERATION On Defender models, at wide open throttle, track 2 returns a signal of 0.28V and track 1 returns a signal of 4.7V to
the ECM. The ECM calculates the sum of these two figures which totals 5.0V.
The ECM uses this strategy to error check the TP sensor signal and ensure that the requested throttle position is
applied. The third potentiometer track measures the tolerance of tracks 1 and 2 and provides an improved
functionality check of the pedal angle.
NOTE: Three track TP sensors cannot be fitted as replacements on vehicles previously fitted with
two track TP sensors. Replacement ECM’s are configured for two track TP sensors and can be
fitted to all Td5 models. When replacement ECM’s are fitted to vehicles using three track TP
sensors, TestBook must be used to configure the ECM for three track TP sensor use.
If the TP sensor fails, the ECM will illuminate the MIL and the engine will operate at normal idle speed only.
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DESCRIPTION AND OPERATION This page is intentionally left blank
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