The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from the engine load (intake manifold vacuum) and the RPM changes then converts these into a voltage output. The Powertrain Control Module (PCM) supplies a 5 volt reference voltage to the MAP sensor. As the manifold pressure changes, the output voltage of the sensor also changes. By monitoring the sensor output voltage, the PCM knows the manifold pressure. A lower pressure (low voltage) output voltage will be about 1.0 to 1.5 volts at idle. While high pressure (high voltage) output voltage will be about 4.5 to 4.8 volts at Wide Open Throttle (WOT). The MAP sensor is also used, under certain conditions, to measure barometric pressure, allowing the PCM to make adjustment for different altitudes. The PCM uses the MAP sensor in order to control the fuel delivery and the ignition timing.