Discovery II (LT) V8-4.0L (2002)
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MAF Output
If the MAF sensor fails, the ECM implements a back up strategy which is based on throttle angle. Poor throttle response and reduced performance will
result.
The MAF sensor can fail the following ways or supply incorrect signal:
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Sensor open circuit.
^
Short circuit to vehicle supply.
^
Short circuit to vehicle earth.
^
Contaminated sensor element.
^
Damaged sensor element.
^
Air leak after the MAF sensor.
^
Inlet air restriction.
^
Resistance in wiring harness causing signal offset.
In the event of a MAF sensor signal failure any of the following symptoms may be observed:
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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:
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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:
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.
