Manifold Pressure/Vacuum Sensor: Description and Operation

Manifold Absolute Pressure (MAP) Sensor:

The Barometric/Manifold Absolute Pressure (BP/MAP) sensor is mounted in the engine compartment and connected to an intake manifold vacuum source via a vacuum line.
The BP/MAP sensor is a frequency generating device that produces a signal between 92 Hz (high engine vacuum) and 162 Hz (low engine vacuum). The Electronic Control Assembly (ECA) monitors the frequency emitted from the BP/MAP sensor and converts the signal to manifold absolute pressure.
The BP/MAP sensor also measures barometric pressure when the key is ON and the engine is NOT RUNNING (after key ON but before engine STARTS) and at WIDE OPEN throttle (WOT). Since the difference between manifold pressure (at WIDE OPEN throttle) and atmospheric pressure is very predictable for a given engine design, the ECA converts the WOT pressure reading to atmospheric pressure. The ECA uses this reading to update the barometric pressure value stored in RAM memory.
The ECA uses the input from the BP/MAP sensor to optimize the air/fuel ratio, ignition timing adjustment, and EGR flow control.
The BP/MAP sensor will also set a fault code when the ECA determines the output signal to be out of the normal operating range.