MAP - Manifold Absolute Pressure

The MAP sensor produces a low signal voltage when manifold pressure is low (high vacuum) and a high voltage when pressure is high (low vacuum).
When ignition is on with the engine off, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the ECM as an indication of vehicle altitude and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a suspect sensor. Reading should be within 400mv of each other.
MAP sensors have a colored plastic insert visible in the connector cavity. Sensors with the same insert color are identical in calibration. The harness electrical connector should also be the same as the insert color.