Manifold Absolute Pressure (MAP) Sensor

WARNING: This page is about a different car, the 2004 Ford Pickup, 2004 Ford F550 Super Duty, 2004 Ford F450 Super Duty, 2004 Ford Excursion, and 2004 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

The manifold absolute pressure (MAP) 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 MAP sensor measures boost pressure. The PCM monitors this signal and adjusts EPC pressure.