Anomaly diagnosing apparatus and anomaly diagnosing method for vehicle on-board internal combustion engine

An anomaly diagnosing apparatus for a vehicle on-board internal combustion engine, wherein

• the vehicle on-board internal combustion engine includes:
• a forced-induction device that includes a compressor wheel;
• an intake passage for conducting intake air into the vehicle on-board internal combustion engine;
• a blow-by gas passage that connects a portion of the intake passage that is upstream of the compressor wheel to an interior of a crankcase;
• and
• a PCV pressure sensor that is disposed in the blow-by gas passage and detects a pressure in the blow-by gas passage as a PCV pressure,
• a period during which an intake fluctuation amount, which is a fluctuation amount of an intake air amount per unit time, is greater than or equal to a specified value is defined as a specific period, and
• the anomaly diagnosing apparatus comprises processing circuitry that is configured to execute:
• a first process of calculating a pressure fluctuation amount, which is a fluctuation amount of the PCV pressure in the specific period;
• a second process of correcting the pressure fluctuation amount to a smaller value when the intake air fluctuation amount in the specific period is relatively large than when the intake air fluctuation amount is relatively small;
• a third process of determining, based on the corrected pressure fluctuation amount, whether there is an anomaly in a portion of the blow-by gas passage between a section in which the PCV pressure sensor is installed and a portion that is connected to the intake passage;
• and
• control the vehicle on-board internal combustion engine based upon the determination as to whether there is the anomaly in the portion of the blow-by gas passage between the section in which the PCV pressure sensor is installed and the portion that is connected to the intake passage.