So if the sensor is defective or out of calibration, drivability, performance and emission problems can occur. Engines that do not have a MAP sensor estimate engine load using input from the airflow sensor and throttle position sensor. HOW THEY WORK MAP sensors read engine vacuum through a hose connected to the intake manifold. A pressure sensitive ceramic or silicon element and electronic circuit inside the sensor generates a voltage signal that changes with vacuum. The sensor's output voltage will vary depending on the application, but a typical reading might be 1.25 volts at idle and just under 5 volts at wide open throttle.
Voltage reads low when vacuum is high, and increases as vacuum drops.
Output generally changes about 0.7 to 1.0 volts for every 5 inches of mercury change in vacuum. The Differential pressure type acts the same as a conventional MAP sensor except the voltage is low with low vacuum and high with high vacuum. Reverse of the normal MAP sensor. Turbo application MAP sensors also vary slightly as they typically read about 2.5 VDC with no vacuum with voltage going up or down as the vehicle goes from a vacuum to boost condition. Ford MAP sensors work somewhat differently in that a digital frequency signal is produced rather than an analog D.C. voltage signal.