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 is measured by the Inlet Air Temperature/Pressure Sensor, which is located on the Air Cleaner Assembly. There is a key on check and a rationality check. At key on, the readings for the Intake Manifold Pressure Sensor, Exhaust Gas Pressure Sensor, and Inlet Air Pressure Sensor are compared. This fault code occurs if the inlet air pressure reading is different from the other two. During normal engine operation the rationality check verifies the inlet air pressure is reading an unreasonable value for a calibrated period of time then an error is recorded. The key-on portion of the rationality will light the MIL immediately after the diagnostic runs and fails. The rationality portion is a one trip fault. During this time the Powertrain Control Module (PCM) uses an estimated barometric pressure. The PCM turns off the MIL when the diagnostic runs and passes in four consecutive drive cycles.