Manifold Absolute Pressure (MAP) Sensor
The Manifold Absolute Pressure (MAP) sensor measures changes in intake manifold pressure which results from engine load and speed changes, and converts this to a voltage output. See Fig 1 .
The MAP output voltage is scaled by PCM to pressure (kPa). A high pressure (atmospheric pressure) will produce an output of about 4.5-5.0 volts, about 95-105 kPa. A low pressure (engine vacuum) will produce about .5-.90 volts, about 37-50 kPa. Manifold Absolute Pressure (MAP) is OPPOSITE of what you would measure on a vacuum gage. When manifold pressure is high, vacuum is low.
The MAP sensor is also used to calculate barometric pressure under certain conditions, which allows PCM to use MAP sensor to provide BARO input. As manifold pressure changes, electrical output of sensor also changes. A higher pressure, low vacuum (high voltage) requires more fuel, while a lower pressure, higher vacuum (low voltage) requires less fuel. By monitoring sensor output voltage, PCM knows manifold pressure and can increase or decrease injector "ON" time (or pulse width) to compensate for addition or reduction of fuel as required. The PCM also uses MAP sensor to control ignition timing. A failure in MAP sensor circuit should set a Code E031, E032, or Code E034.