The mass air flow sensor is placed in the stream of intake air. It converts the amount of air drawn into the engine into a voltage signal, The Engine Control Module (ECM) need to know intake air volume to calculate engine load. This is necessary to determine how much fuel to inject, when to ignite the cylinder, an when to shift the transmission.
There are different types of Αir Flow Meter (Αir Flow Sensor, Mass Αir Flow Sensor), but the more common is the Mass Αir Flow (MΑF) sensor.
It consists of a hot film that is supplied with electric current from the ECM. The temperature of the hot film is controlled by the ECM a certain amount. The heat generated by the hot film is reduced as the intake air flows around it. The more air, the greater the heat loss. Therefore, the ECM must supply more electric current to maintain the temperature of the hot film as air flow increases. The ECM detects the air flow by means of this current change.