Air Flow Meter/Sensor: Description and Operation

OPERATION

The Mass Airflow (MAF) sensor is a frequency based device. A constant voltage is applied to a heated wire on the sensor. This wire is positioned in the air cleaner air stream and is heated by the electrical current that the voltage produces. As air flows across it, it cools down. The heated wire or film is a positive temperature coefficient resistor. This means that its resistance drops when its temperature drops. The drop in resistance allows more current to flow through it in order to maintain the programmed temperature. This current is changed to a frequency which is sent to the Engine Control Module (ECM) and interpreted as air flow. Adjustments for air temperature and humidity are taken into consideration because they also affect the temperature of the heated wire or film.