The air flow mass meter is an electronic air flow sensor, also referred to as an air flow mass sensor, which measures air flow; the mass of air which is flowing through the car's engine, and is an important part of the car's Engine Control Unit (ECU).  The air flow mass meter has an important part to play in the performance, power and efficiency of the engine.

The air flow mass meter is usually found in the plastic housing between the engine and the air filter, connected by the air metering pipe.

The engine needs the correct amount of air and fuel flowing through it in order for the fuel to burn in the cylinders and for the engine to ignite or spark at the right time. If the ignition sparks at the wrong time, there will be less power in the engine and it will try to make up for this by using more fuel, significantly reducing fuel efficiency, which in turn increases the car's CO2 emissions. The air flow mass meter works by measuring the air flow and sending these measurements to the ECU which, based on these measurements, controls the amount of fuel flowing into the engine at the point at which the ignition sparks.

The air flow mass meter will, over time, wear out or stop working. When this happens, the performance of the engine is likely to be affected and engine emissions will be higher. A fault in the air flow mass meter will cause the Check Engine light to show on the dashboard to indicate a malfunction with the air flow mass meter. A broken air flow mass meter can sometimes prevent a car from idling properly (the ability for a car's engine to run whilst it is not moving) and may cause the engine to splutter and stall. If there is a fault in the air flow mass meter a replacement air flow mass meter should be purchased.