Diagnosing apparatus and diagnosing method for internal combustion engine

A diagnosing apparatus for an internal combustion engine, wherein the internal combustion engine is configured to execute a specific-cylinder fuel cutoff process in which combustion in part of cylinders is stopped and combustion is continued in the remaining cylinders, and the diagnosing apparatus comprises

• a processing circuitry, wherein the processing circuitry is configured to execute
• a misfire anomaly diagnosing process of diagnosing whether there is a misfire anomaly in the internal combustion engine based on a misfire frequency of the internal combustion engine,
• a normality restoration diagnosing process of diagnosing, in a state in which it is diagnosed that there is a misfire anomaly, that the misfire anomaly has been resolved when a measured value of the misfire frequency becomes less than or equal to a specified normality restoration determination value, and
• a storing process of storing an operating state of the internal combustion engine at the time of diagnosis of the misfire anomaly, and
• the normality restoration diagnosing process is configured to stop measurement of the misfire frequency and to not diagnose that the misfire anomaly has been resolved in a case in which the operating state of the internal combustion engine stored in the storing process does not agree with a current operating state of the internal combustion engine, and the operating state of the internal combustion engine stored in the storing process includes whether the specific-cylinder fuel cutoff process is being executed.

A diagnosing method for an internal combustion engine, wherein

• the internal combustion engine is configured to execute a specific-cylinder fuel cutoff process in which combustion in part of cylinders is stopped and combustion is continued in the remaining cylinders, and
• the diagnosing method comprises:
• diagnosing whether there is a misfire anomaly in the internal combustion engine based on a misfire frequency of the internal combustion engine;
• diagnosing, in a state in which it is diagnosed that there is a misfire anomaly, that the misfire anomaly has been resolved when a measured value of the misfire frequency becomes less than or equal to a specified normality restoration determination value;
• and
• stopping measurement of the misfire frequency and not diagnosing, during the execution of the specific-cylinder fuel cutoff process, that the misfire anomaly has been eliminated.