Manifold Pressure/Vacuum Sensor: Description and Operation

Fig. 5 Barometric & Manifold Absolute Pressure Sensor:

These two sensors, Fig. 5, are combined into one unit. The BMAP sensor monitors the absolute value of the intake manifold pressure and atmospheric pressure (manifold absolute pressure is defined as barometric pressure minus manifold vacuum).
Atmospheric pressure changes are converted into an electrical signal and fed to the computer for evaluation. From this input, the computer determines the EGR flow requirements depending on the altitude at which the vehicle is being operated.
Intake manifold pressure changes are converted by a pressure-sensing element and electrical circuit by the computer. The signal is used by the computer to determine part throttle spark advance, EGR flow rate and air/fuel ratio.