Manifold Absolute Pressure (MAP) Sensor

The MAP sensor is a variable resistor which measures the changes in the intake manifold pressure which result from engine load and speed changes. The pressure measured by the MAP sensor is the difference between barometric pressure (atmospheric air) and manifold pressure (vacuum).

A closed throttle condition (engine coast down) would produce a low MAP reading while a wide open throttle condition (engine acceleration) would produce a high MAP reading. The high value is produced because the pressure inside the intake manifold (vacuum) is the same as the pressure outside the manifold (atmospheric air).

The ECM supplies a 5-volt reference signal to the MAP sensor. As MAP changes, the electrical resistance of the sensor also changes. By monitoring sensor output voltage, the ECM is informed of intake manifold pressure. A higher pressure (high voltage) requires more fuel, while a lower pressure (low voltage) requires less fuel.