Circuit/System Description

The manifold absolute pressure (MAP) sensor measures the pressure inside the intake manifold. Pressure in the intake manifold is affected by turbocharger output, engine speed, accelerator pedal input, air temperature, and barometric pressure (BARO). A diaphragm within the MAP pressure sensor is displaced by the pressure changes that occur from the varying load and operating conditions of the engine. The sensor translates this action into electrical resistance. The MAP pressure sensor wiring includes 3 circuits. The engine control module (ECM) supplies a regulated 5-volt reference circuit, a ground on a low reference circuit, and the MAP pressure sensor provides a signal voltage to the ECM, relative to pressure on the signal circuit. The ECM converts the signal voltage input to a pressure value. Under normal operation the lowest pressure that can exist in the intake manifold is equal to the BARO. This occurs when the vehicle is operated at idle or when the ignition is on while the engine is off. The highest manifold pressures occur when the turbocharger output is high. Manifold pressure can range from 58 kPa (8 psi) when pressures are low to more than 240 kPa (34 psi) when pressures are high, depending on the BARO. The MAP pressure sensor has a range of 33 kPa (4 psi) to 255 kPa (36 psi). The ECM monitors the MAP sensor, by comparing a calculated predicted value at a predetermined engine load and speed, to the actual input.