The Mass Air Flow Sensor (MAF) is one of the key components of an electronic fuel injection system in your car. It is installed between the air filter and the intake manifold of the engine. The MAF Sensor measures the amount of air entering the engine or the air flow.
In modern cars, an Intake Air Temperature or IAT sensor is built in the mass air flow sensor.
A hot-wire mass air flow sensor has a small electrically heated wire (hot wire). A temperature sensor installed close to the hot wire measures the temperature of the air near the hot wire.
When the engine is idling, a small amount of air flows around the hot wire, so it takes a very low electric current to keep the wire hot. When you press the gas, the throttle opens allowing more air to flow over the hot wire.
The passing air cools the wire down. The more air flows over the wire, the more electrical current is needed to keep it hot. The electric current is proportional to the amount of air flow. A small electronic chip installed inside the air flow sensor translates the electric current into a digital signal and sends it to the engine computer (PCM).
The PCM uses the air flow signal to calculate how much fuel to inject. The goal is to keep the air/fuel ratio at the optimal level.
Problems with mass air flow sensors are common in many cars, including BMW, GM, Volkswagen, Mazda, Toyota, Nissan and other brands. The sensor element could get contaminated or damaged.
For example, in some Mazda Skyactiv engines, a failed mass air flow sensor could cause the engine to crank but not to start.
An improperly installed or collapsed air filter can cause the air flow sensor to fail sooner. Over-soaking a washable air filter can also cause problems with the air flow sensor.