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, ambient 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 these changes into electrical resistance. The Engine Control Module (ECM) supplies a regulated 5 volts on the 5 volt reference circuit and a ground on a low reference circuit. The MAP sensor provides a signal voltage to the ECM, relative to intake manifold pressures, on the MAP sensor 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 throttle is not being used, and while the vehicle is operated at idle or when the ignition is On, and 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 greater than 276 kPa (40 psi) when pressures are high, depending on the BARO. The MAP pressure sensor has a range of 0 - 365 kPa (0 - 46.8 psi). The ECM monitors boost deviation by comparing a calculated value at a predetermined engine load and speed, to the actual sensor input.