Manifold Pressure/Vacuum Sensor: Description and Operation

MAP Sensor:

The Manifold Absolute Pressure (MAP) Sensor measures the changes in intake manifold pressure resulting from engine load and speed changes, converting this to an ECM voltage input signal. This signal ranges from about 1.0 - 1.5V at idle to 4.0 - 4.5V at wide open throttle.

A closed throttle on deceleration produces a relatively low MAP output, while wide open throttle produces a high output. This high output is produced because the pressure inside the manifold is the same as outside the manifold, resulting in a measurement of 100% of outside air pressure.

Manifold absolute pressure is the OPPOSITE of engine manifold vacuum. When manifold pressure is high, vacuum is low. The MAP sensor also measures barometric pressure under certain conditions, enabling the ECM to make adjustments for altitude changes. High pressure (low vacuum and high voltage) requires more fuel. Low pressure (high vacuum and low voltage) requires less fuel.

The ECM uses the MAP sensor input signal in its calculations for fuel delivery and ignition timing.