Manifold Absolute Pressure Sensor
The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. MAP sensor is mounted on top of intake manifold. See Fig 1 . The pressure changes occur based on engine load. The MAP sensor has a 5-volt reference circuit, a low reference circuit and a signal circuit. The PCM supplies 5 volts to MAP sensor on the 5-volt reference circuit. PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. PCM should detect a high signal voltage at a high MAP, such as when ignition is on, with engine off or at a Wide Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric Pressure (BARO). This occurs when ignition is on, with engine off. The BARO reading may also be updated whenever engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If PCM detects a MAP sensor signal voltage that is out-of-range, a DTC will set. To diagnose DTC, see SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.
If MAP sensor fails, the PCM substitutes a fixed MAP value, and uses the TP sensor to control fuel delivery. A fault in the MAP circuit should set a related diagnostic trouble code.