Air Flow Meter/Sensor: Description and Operation

Mass Air Flow Sensor:

The Mass Air Flow Sensor (MAF), located on the right side of the engine compartment, is a hot wire type sensor. Unlike a flap type air flow sensor which only measures air flow volume, a mass air flow sensor measures the actual mass per unit time of air entering the engine. This is a more accurate measurement because any given volume contains different quantities of air depending on the air density.

The sensor converts the amount of air taken into the engine to an electric signal by using the heat transfer phenomenon between incoming air and a heated resistor (wire). The ECU uses this information, together with input data from other sensors, to calculate fuel injector pulse ("ON" time) and thus regulate air/fuel ratio.

The sensing element is a thin platinum wire wound on a ceramic bobbin and coated with glass. This hot wire is maintained at 200°C (392°F) above ambient temperature as measured by a cold wire. By measuring the amount of current required to maintain hot wire temperature, the ECA can calculate the mass of air entering the engine.