| 摘要 |
An exhaust gas purifying system includes a catalyst arranged on an exhaust pipe of an internal combustion engine; a sensor detecting a state of the exhaust gas passed through the catalyst; and an ECU functioning as an abnormality determining apparatus determining abnormality by monitoring an output of said sensor in an operation under forced air-fuel ratio. When the operation under forced air-fuel control is interrupted before completion of the determination of system abnormality, the abnormality determining apparatus once stores a parameter accumulated during the operation under forced air-fuel ratio control by the time of interruption, and when the internal combustion engine comes to satisfy the prescribed condition again, resumes the operation under forced air-fuel ratio control, and completes determination of system abnormality using the stored parameter and the parameter accumulated after resumption of the forced air-fuel ratio control.
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