Various embodiments include a method for monitoring the ventilation of a crankcase of an internal combustion engine with combustion chambers and a nitrogen oxide sensor arranged in an exhaust system, the sensor configured to detect an amount of nitrogen oxide in exhaust gas of the internal combustion engine. An example method includes: determining a predefined operating mode of the internal combustion engine defined by substantially no combustion of an air/fuel mixture taking place inside the combustion chambers; determining an amount of nitrogen oxide in the exhaust gas during the predefined operating mode of the internal combustion engine using the exhaust gas sensor; and identifying functional ventilation of the crankcase if the detected nitrogen oxide level exceeds a predefined nitrogen oxide threshold or identifying a malfunction if the detected nitrogen oxide level is below the predefined nitrogen oxide threshold.

An apparatus of diagnosing a blow-by gas recirculation system includes: a head portion of an engine forming a combustion chamber, a head cover provided above the head portion, a crankcase formed below the combustion chamber, an intake line through which intake air flows into the combustion chamber, a breather hose connecting the crankcase and the intake line upstream of a compressor mounted on the intake line, a PCV hose connecting the crankcase and a surge tank, and a controller. The controller is configured to preliminarily determine whether the breather hose is abnormal based on atmospheric pressure, a crankcase model pressure determined from an intake air flow rate flowing in through a throttle valve, and a crankcase internal pressure. The controller is configured to form negative pressure in the crankcase when it is preliminarily determined that the breather hose is abnormal, and finally determine whether the breather hose is abnormal.

An apparatus of diagnosing a blow-by gas recirculation system includes: a head portion of an engine forming a combustion chamber, a head cover provided above the head portion, a crankcase formed below the combustion chamber, an intake line through which intake air flows into the combustion chamber, a breather hose connecting the crankcase and the intake line upstream of a compressor mounted on the intake line, a PCV hose connecting the crankcase and a surge tank, and a controller. The controller is configured to preliminarily determine whether the breather hose is abnormal based on atmospheric pressure, a crankcase model pressure determined from an intake air flow rate flowing in through a throttle valve, and a crankcase internal pressure. The controller is configured to form negative pressure in the crankcase when it is preliminarily determined that the breather hose is abnormal, and finally determine whether the breather hose is abnormal.