Air Flow Meter/Sensor: Description and Operation

The Mass Air Flow (MAF) and Intake Air Temperature (IAT) sensors are combined in to a common assembly located in the air intake assembly. The IAT sensor protrudes through the side of the MAF housing into the intake airflow. The MAF/IAT sensor assembly can be differentiated from the older style MAF sensor by its new 5 wire connector. The Intake Air Temperature (IAT) sensor is a thermistor which changes the value based on the temperature of the air entering the engine. A low temperature produces a high resistance (100,000 ohms at -40°C (-40°F)). A high temperature causes a low resistance (70 ohms at 130°C (266°F)). The VCM supplies a 5 volt signal to the sensor through a resistor in the VCM 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 VCM calculates the incoming air temperature. The AT sensor signal is used in order to adjust the spark timing according to the incoming air density.

The 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. The temperature should rise as the underhood temperature increases. If the engine has not been run for several hours (overnight), the IAT sensor temperature and the engine coolant temperature should read close to each other. If the VCM detects a malfunction in the AT sensor circuit, the following DTCs will set:
^ DTC P0112 circuit low
^ DTC P0113 circuit high
^ DTC P1111 circuit intermittent high
^ DTC P1112 circuit intermittent low

The Mass Air Flow (MAF) sensor measures the amount of air entering the engine. The VCM uses this information to determine the operating condition of the engine in order to control the fuel delivery. A large quantity of air indicates an acceleration. A small quantity of air indicates a deceleration or an idle. The scan tool reads the MAF value and displays the MAF value in grams per second (gm/Sec). At idle, the MAF value should read between 5 gm/sec - 7 gm/sec on a fully warmed up engine. The values should change rather quickly on acceleration, but values should remain fairly stable at any given RPM. When the VCM detects a malfunction in the MAF sensor circuit, the following DTCs will set:
^ DTC P0101 system performance
^ DTC P0102 frequency low
^ DTC P0103 frequency high