Air Flow Meter/Sensor: Description and Operation

Mass Air Flow (MAF) Sensor:

The Mass Air Flow (MAF) sensor measures the amount of air coming into the engine. This direct airflow measurement is more accurate than the calculated airflow information obtained from the other sensor inputs. The MAF sensor has a switched battery feed, a ground, a signal circuit, and a signal return circuit.

The MAF sensor that is used on this vehicle is a hot film type and is used in order to measure the air flow rate. The MAF output voltage is a function of the power required to keep the air flow sensing elements at a fixed temperature above the ambient temperature. The air flowing through the sensor cools the sensing elements. The amount of cooling is proportional to the amount of air flow. As the air flow increases, more current is needed in order to maintain the hot film at a constant temperature. The MAF sensor converts the changes in the current draw to a voltage signal that is read by the Engine Control Module (ECM). The ECM calculates the air flow based on this signal.

The ECM monitors the MAF sensor signal voltage and can determine if the sensor signal voltage is too low or too high. The ECM can also detect airflow that is inappropriate for a given operating condition based on the signal voltage, or a signal that appears to be stuck based on the lack of normal signal fluctuations expected during engine operation.

The scan tool reads the MAF value and displays the value in grams per second (gm/s). Values should change rather quickly on acceleration, but should remain fairly stable at any given RPM. When the ECM detects a malfunction in the MAF sensor circuit, DTC P0100 will set: