Changes in engine speed, and load, cause changes in intake manifold pressure. This sensor measures these pressure changes and converts them into an electrical signal. It’s called a manifold absolute pressure, or MAP, sensor.
The signal may be an output voltage, or a frequency.
By monitoring output voltages, the control unit senses manifold pressure and uses this information to provide the basic fuel requirement.
It can use a piezoelectric crystal. If there is a change in the pressure exerted on this crystal, it changes its resistance. This alters its output signal.
The sensor is connected to the intake manifold by a small-diameter, flexible tube. The control unit sends a 5 volt reference signal to the sensor. As manifold pressure changes, so does the electrical resistance of the sensor, and this in turn produces change in the output voltage.
During idling, manifold pressure is low, which produces a comparatively low MAP output.
With wide open throttle, manifold pressure is closer to atmospheric, so output is higher.
Source: CDX Global
