The Intake Air Temperature (IAT) sensor is a thermistor which changes value based on the temperature of the air entering the engine. Low temperature produces a high resistance (100,000 ohms at -40°F.) while high temperature causes low resistance (70 ohms at 266°F.). The PCM supplies a voltage (about 5.0V) through a pull up resistor to the PCM's IAT signal circuit and measures the voltage. The voltage will be high when the in coming air is cold, and low when the air is hot. By measuring the voltage, the PCM calculates the in coming air temperature. The IAT sensor signal is used to adjust spark timing according to incoming air density.
A technician's scan tool displays the temperature of the air entering the engine, which should read close to the 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 displays should be close to each other. A failure in the IAT sensor circuit should set a Diagnostic Trouble Code.
Check the following items before beginning more in depth diagnosis and testing.
- Turn the ignition switch OFF .
- Disconnect the wiring harness from the IAT sensor.
- Measure the resistance between the sensor terminals.
- Compare the resistance reading with the accompanying chart.
- If the resistance is not within specification, the IAT may be faulty.
- Connect the wiring harness to the sensor.