Grand Prix V6-191 3.1L VIN M SFI (1998)
Intake Air Temperature (IAT) Sensor: Description and Operation
DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor which changes value based on the temperature of air entering the engine. Low temperature
produces a high resistance (100,000 ohms at -40°C/-40°F), while high temperature causes low resistance (70 ohms at 130°C/266°F).
OPERATION
The PCM supplies a 5 volt signal to the sensor through a resistor in the PCM and measures the voltage. The voltage will be high when the incoming
air is cold, and low when the air is hot. By measuring the voltage, the PCM calculates the incoming air temperature. The IAT sensor signal is used to
adjust spark timing according to incoming air density.
SCAN TOOL DIAGNOSIS
The scan tool displays temperature of the air entering the engine, which should read close to ambient air temperature when the engine is cold, and rise
as the underhood temperature increases. If the engine has not been run for several hours (overnight) the IAT sensor temperature and engine coolant
temperature should read close to each other. A failure in the AT sensor circuit should set DTC P0112 or DTC P0113.
