MAF Sensors – How do they work?
June 2, 2024MAF sensors (Mass Air Flow Sensors), measure the amount (mass) of air entering an engine. They measure the air mass indirectly, by measuring the temperature difference of a wire or film inside the sensor.
This article deals with hot wire MAF sensors (and hot film sensors that output a voltage).
The Flow Sensing Process
The sensing wire is heated by a constant voltage.
The temperature of the wire changes according to how much air is passing over it.
The resistance of the wire changes according to it’s temperature.
The amount current passing through the wire changes according to it’s resistance.
The MAF sensor measures the current flowing through the wire/film and outputs a voltage signal which represents air flow. This signal is used by the engine ECU.
The higher the resistance of the wire, the less current flows through the wire.
https://www.allaboutcircuits.com/textbook/direct-current/chpt-2/analogy-ohms-law/
More Air Flow
When the mass of air passing through the sensor increases, the wire gets cooler. As the wire gets cooler the resistance decreases allowing more current to pass through the wire, the MAF sensor measures this and outputs a higher voltage to the engine ECU.
Less Air Flow
As air flow decreases, the wire temp increases, resistance increases, current decreases, MAF sensor outputs a lower voltage.
Different Types of MAF Sensors
There are more types of sensor, read more here.
