Mass Air Flow Sensor (MAF)

Located between the air filter and the throttle body, the MAF measures the mass of air flowing in. Fuel is calculated from it, so an inaccurate reading directly affects the mixture. Some engines use a manifold absolute pressure (MAP) sensor instead or alongside. Diesels use the MAF reading to control EGR as well.

Most sensors use a heated film or wire: incoming air cools the element, and the current needed to keep it hot shows how much air is flowing. Air leaks between the sensor and the engine, a dirty air filter or an oiled performance filter can all make a good MAF sensor appear faulty. Comparing its reading in live data with the expected value for the engine size and speed is a useful first check before buying a new sensor.

Most sensors use a heated element: air flowing past cools it, and the electronics measure how much current is needed to keep it at a set temperature. Some engines use a manifold absolute pressure (MAP) sensor instead of, or as well as, a MAF sensor to calculate air mass.

A dirty or failing MAF causes hesitation, poor power, lean or rich codes and stalling, with codes such as P0101 or P0102. Air leaks after the sensor also confuse it, because that air is never measured. A dirty or failing MAF sensor can cause hesitation, poor power, black smoke on diesels and lean or rich codes. Cleaning with a dedicated sensor cleaner sometimes helps; never touch the element.