Manifold Absolute Pressure (Map) Sensor - Gasoline Engines

WARNING: This page is about a different car, the 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, 2003 Ford Excursion, and 2003 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

On gasoline engines, 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.