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

Intake Air Temperature Sensor:

The Manifold Air Temperature (MAT) sensor is a thermistor (a resistor which varies resistance inversely with a change of temperature). Low coolant 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. The ECM supplies a 5.0 volts signal to the MAT sensor through a resistor in the ECM and measures the voltage. The voltage will be high when the intake air is cold, and low when the intake air is hot. By measuring the voltage, the ECM knows the manifold air temperature. The MAT sensor is also used to control spark timing and delays EGR when intake air is cold. A failure in the MAT sensor circuit should set either a Code 23 or a Code 25.