How do mass airflow (MAF) sensors work?

MAF sensors measure intake air mass flow for accurate fuel calculation. Hot-wire/hot-film type sensors maintain a heated element at constant temperature above ambient; airflow cools the element, requiring more current to maintain temperature - this current is proportional to mass flow. Karman vortex type creates vortices and measures their frequency. MAF sensors output analog voltage or digital frequency to the ECU. They are self-calibrating for air density changes with altitude and temperature, making them preferred over manifold pressure-based calculations.