Theory of operation

WARNING: This page is about a different car, the 2011 RAM Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

The barometric pressure (BARO) sensor is the Manifold Absolute Pressure (MAP) sensor which is a transducer that varies resistance according to changes in altitude and atmospheric conditions. The BARO reading, which is read the first few moments before engine cranking, gives the Powertrain Control Module (PCM) an indication of the current barometric pressure. The PCM uses this information to calculate fuel delivery. The MAP sensor has a 5 Volt reference circuit, a low reference circuit and a signal circuit. The PCM supplies 5 Volts to the MAP sensor on a 5 Volt reference circuit and provides a ground on a low reference circuit. The MAP sensor provides a voltage signal to the PCM on a signal circuit relative to the pressure changes. The PCM monitors the stability of the BARO reading output by comparing successive samples.