Air Flow Meter/Sensor: Description and Operation

PURPOSE AND OPERATION
The hot-wire Mass Air Flow Sensor (MAFS) is designed to accurately measure intake air entering the engine. This allows for precise fuel mixture control at all engine speed/load ranges.

The air flow sensor consists of a cast alloy body through which air flows. A proportion of this air flows through a bypass in which two wire elements are situated. One is a sensing wire and the other is a compensating wire. Under the control of an electronic module which is mounted on the air flow sensor body, a small current is passed through the sensing wire to produce a heating effect. The compensating wire is also connected to the module but is not heated, but reacts to the temperature of the air taken in, as engine intake air passes over the wires a cooling effect takes place.

The electronic module monitors the reaction of the wires in proportion to the air stream and provides output signals in proportion to the air mass flow rate which are compatible with the requirements of the engine control module (ECM).