How air flow meters work
The simplest description of the internal combustion engine is that of an air pump. Air enters the cylinders, mixes with fuel, burns to create explosive energy, and is then pushed out. The key to efficient combustion is a specific air-to-fuel ratio, a problem in the old days of carburetors. Modern fuel injection requires proper metering of the air entering the engine so that the computer can match it with the relevant amount of fuel. There are several strategies to do so, one of which is the Air Flow Meter (AFM) or Mass Air Flow Sensor (MAF). Located after the intake, it accurately monitors the volume and density of the air entering the motor.

Air flow meter types
There are two main types of MAFs, Hot Wire, and Vane. Further divided into the sub-group digital and analog, is the Hot Wire AFM. The VAFM uses a small spring-loaded trap door, or flap, to meter the air entering the engine. As airflow increases with engine speed, this causes the flap/door to open more to allow the air through. Connected to a potentiometer, the VAFM’s flap/door makes it send a variable electrical signal to the ECU based on how open it is. It however, cannot measure the air density. To do this an air temperature sensor gets paired inside the VAF assembly.

 The internal construction of Hot wire AFMs is their main method of identification. Analog AFMs use a single wire mounted in the air stream and output is a variable voltage signal. Those that are digital have mesh screens with a frequency output signal. Both still operate on the same theory. The wire or mesh, receives an electrical current that heats it up. The ability of the incoming air to cool the electronically heated media translates any base changes in temperature into the output data for the ECU. Cooler means less resistance, more airflow, and vice-versa. The Hot Wire AFM doesn’t need an air temperature sensor since air density, higher or lower oxygen count, also plays a part in cooling capability.

Irrespective of which Air Flow Meter design, they all do the important job of telling the electronic control unit (ECU) the exact amount of air and its density entering the engine. This allows it to react by delivering the correct amount of fuel via the injectors to match the incoming air. The engine will then meet power, fuel efficiency, and emissions requirements as per the manufacturer’s specifications.