Manifold Absolute Pressure (MAP) Sensor
WARNING: This page is about a different car, the 2004 Ford Econoline, 2004 Ford E450 Super Duty, and 2004 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
On gasoline engines, the manifold absolute pressure sensor senses atmospheric pressure to produce an electrical signal. The frequency of this signal varies with intake manifold pressure. The powertrain control module (PCM) monitors this signal to determine altitude. The PCM then adjusts the transmission shift schedule and EPC pressure for altitude. On diesel engines, the manifold absolute pressure (MAP) sensor measures boost pressure. The PCM monitors this signal and adjusts EPC pressure.