Discovery II
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:
l
Sensor open circuit.
l
Short circuit to vehicle battery supply.
l
Short circuit to vehicle earth.
l
Increased sensor resistance.
l
Damaged sensor element.
In the event of an IAT sensor signal failure any of the following symptoms may be observed:
l
Adaptive fuelling disabled.
l
Idle speed adaption disabled.
l
Catalyst monitoring affected due to exhaust temperature model.
l
Idle speed actuator test disabled.
l
Warm up ignition angle affected.
l
Condenser fan hot restart inhibited.