Air Temperature Sensor ( Ambient / Intake ): Testing and Inspection

Description:

Following is a short description of how the Intake Air Temperature (IAT) sensor can be diagnosed by using a scan tool. The scan tool can also be used to compare the values for a normal running engine with the engine you are diagnosing.

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 ohm at -40°C/-40°F), while high temperature causes low resistance (70 ohm 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.


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 IAT sensor circuit should set DTC P0112 or DTC P0113. Refer to System DIagnosis / Diagnostic Tables / Diagnostic Trouble Code Tables. Testing and Inspection