How do you test a map sensor on a car?

A m.a.p or manifold absolute pressure sensor can be tested with a scan tool on 1996 and later vehicles. This sensor is found only on some vehicles. Others have a m.a.f sensor (mass air flow). These sensors measure air flow before entering the engine and send the info to the pcm (computer). If the m.a.p sensor is faulty you may or may not have a "check engine" light illuminated.