Barometric Pressure Sensor: Description and Operation

Barometric Absolute Pressure Sensor (BAP):

The Barometric Absolute Pressure Sensor (BAP), located on the firewall right of center, provides the ECA with two types of information. With engine running, the sensor reads pressure changes in the intake manifold with reference to zero or absolute vacuum. This measurement is referred to as manifold absolute pressure (MAP) and provides the ECA with engine load information. The sensor is also used as a barometric sensor for altitude compensation of ECA outputs such as air/fuel ratio. The sensor updates the ECA with altitude information each time the ignition is switched "ON" (before engine start) and whenever a wide open throttle (WOT) condition is detected.

MAP is the OPPOSITE of engine intake manifold vacuum. When manifold pressure is high, vacuum is low. A closed throttle on deceleration produces a relatively low BAP sensor output, while WOT produces a high output. During WOT, high output is produced bacause pressure inside and outside the manifold is the same, resulting in a measurement of 100% of outside air pressure.