What is a Mass Air Flow Sensor?

A Mass Air Flow Sensor (MAF) is a device that measures the volume and density of the air entering the engine.  It is the first sensor to read the amount of air entering the motor. The MAF is made up of an air temperature sensor, an electronic control unit, and a hot wire.  The main job of this sensor is to convert the amount of air coming into the vehicle into a voltage signal.  Along with the assistance of oxygen sensors, the MAF provides the Engine Control Unit (ECU) with vital information. This data lets the ECU know how much fuel to inject, the timing of ignition, and when to shift a transmission.

There are two main types of mass air flow sensors in automotive engines, the vane meter and the hot wire. The vane meter is an older style.  It measures the amount of air with a spring loaded flap attached to a resistor.  The vane meter is not used as often as the hot wire because it restricts airflow, the moving parts wear easier, and finding a space to mount it is difficult. On the other hand, the hot wire style has minimal airflow resistance, it’s smaller, it has no moving parts that wear, and it responds very quickly to changes in air flow.  So, basically the hot wire is a skinnier, smarter version of the vane meter.

If your Mass Air Flow Sensor is malfunctioning your car may idle erratically, run lean, try to stall, and the throttle could decrease at highway speeds.  If you have a digital scanner you can make sure that your MAF is to blame by hooking the scanner up to the housing circuit and checking for codes. In some cases the sensor is just dirty and needs to be cleaned, but more commonly the part is broken.  MAFs are rarely repairable and a new one will run you a couple hundred dollars.