Recently I penned an article for StarTuned magazine on mass air flow sensors. The article itself is written in a highly technical format as it is intended for use by experienced automotive technicians. What follows here is more of a laymen’s version to give a brief overview of how this system is designed for use in your car.

Now you might be thinking, who cares? I know most folks want to put their key in the ignition or push the start button and drive away. What goes on under the hood doesn’t matter as long as they can get where they’re going. I remember some years ago at the place of business where my wife worked a company was washing their cars for them. They asked her which car was hers and she replied “the red one”. It just wasn’t important to her to know the make and model, only that it was kept running well. And so it is with the lowly mass air flow sensor, a very important part of your cars combustion system but not many people know they even have one. If you drive a car that was built within the last 20 years then you have one.

modern day mass air flow sensor

All modern cars on the road today are fuel injected. In order for the ideal combustion to take place the proper amount of fuel needs to be mixed with the proper amount of air entering the engine. The processor or the engine control module can calculate and dispense the proper amount of fuel through the injectors but how does it know how much air is entering the engine? This is where the mass air flow sensor comes in.

A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system. This is achieved by heating a wire suspended in the engine’s air stream, like a toaster wire, with either a constant voltage over the wire or a constant current through the wire. The wire’s electrical resistance increases as the wire’s temperature increases, which varies the electrical current flowing through the circuit, according to Ohm’s law. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit, since the supply voltage is a constant. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The current increase or decrease is proportional to the mass of air flowing past the wire. The integrated electronic circuit converts the proportional measurement into a calibrated signal which is sent to the engine control unit or ECU.

This may seem like more information than you need but what you do need to know is that the mass air flow sensor or MAF is located between the air filter and your engine. Therefore it is important to keep the air filter in your car clean and in good condition. We have actually seen filters of inferior quality cause the MAF to send an improper air flow signal to the car’s ECU resulting in poor performance and mileage.

clean air filter