Lanos S Hatchback L4-1.6L DOHC D-TEC MFI (1999)
Intake Air Temperature (IAT) Sensor: Description and Operation
The intake air temperature (IAT) sensor is a thermistor, a resistor which changes value based on the temperature of the air entering the engine. Low
temperature produces a high resistance (100,000 ohms at -40 °C [-40 °F]), while high temperature causes a low resistance (70 ohms at 130 °C [286 °F]
).
The powertrain control module (PCM)/engine control module (ECM) provides 5 volts to the IAT sensor through a resistor in the PCM/ECM and
measures the change in voltage to determine the intake air temperature. The voltage will be high when the manifold air is cold and low when the air is
hot. The PCM/ECM knows the intake air temperature by measuring the voltage.
The IAT sensor is also used to control spark timing when the intake air is cold.
A failure in the IAT sensor circuit sets a diagnostic trouble code P1111 or P1112.
