A MAP (manifold absolute pressure) sensor is a component used in the speed-density method to accurately determine the mass of air entering an engine.
Accurate and precise air mass measurement is required to meter fuel mass in a manner that will achieve acceptable emissions under all operating conditions.
The MAP sensor monitors intake manifold pressure (engine load ). The change in manifold air pressure is measured to determine the load on the engine, a high vacuum reading indicates a low load and a low vacuum or positive pressure (boost) indicates a high load.