Theory Of Operation

WARNING: This page is about a different car, the 2015 Fiat 500. However, it is still accessible from the selected car via links, so may be relevant.

When the engine is running and not in boost, the crankcase ventilation hose provides filtered clean air from the clean air tube to the PCV system through the crankcase. During boost the flow reverses and PCV vapors are pushed from the crankcase, through the tube, into the clean air tube, then into the Supercharger, and eventually into the Intake Manifold where they are burned. If the crankcase ventilation hose is disconnected from the clean air tube, PCV vapors will leak into the atmosphere whenever the engine is in boost.

The PCM will run a diagnostic to determine if the crankcase ventilation hose is disconnected. This monitor only runs for a short time during engine cranking and initial start up. The Crankcase Pressure Sensor is connected to the crankcase ventilation hose fitting on the clean air tube. When the clean side of the PCV system is intact, the sensor will detect the pressure pulsations coming through the tube and the diagnostic monitor will pass. If any part of the clean air side is disconnected or restricted, the sensor will not see the pulsations and the diagnostic monitor will fail. If the sensor is stuck in range, and does not change when the diagnostic monitor is running, the diagnostic will fail.