Air Temperature Sensor ( Ambient / Intake ): Description and Operation

Component Locations:

Intake Air Temperature Sensor Circuit:

PURPOSE
By monitoring the Intake Air Temperature (IAT) voltage, the Engine Control Module (ECM) calculates the air temperature and uses this data to assist in determining fuel delivery and spark advance.

OPERATION
The IAT sensor uses a thermistor to control the signal voltage to the ECM. The variable resistor changes its resistance based on temperature. Low intake air temperature produces high resistance, 100,000 ohms at -40°C (-40°F), while a high temperature causes low resistance, 70 ohms at 130°C (266°F). The ECM supplies a 5.0 volt signal to the IAT sensor through a resistor in the ECM and monitors the voltage change.

SCAN TOOL DISPLAY
A scan tool displays temperature of the air entering the engine and should display close to ambient air temperature, when engine is cold, and rise as underhood temperature increases. If the engine has not been run for several hours (overnight), the IAT sensor temperature and Engine Coolant Temperature (ECT) sensor temperature readings should be close to each other.

DTC SET ON CIRCUIT FAILURE
A failure in the IAT sensor circuit should set a Diagnostic Trouble Code (DTC) 23 or DTC 25. The DTC charts also contain a chart to check for sensor resistance values relative to temperature.