Abnormality diagnosis device for positive crankcase ventilation apparatus

An abnormality diagnosis device for diagnosing abnormality in a positive crankcase ventilation apparatus, in which the positive crankcase ventilation apparatus includes a positive crankcase ventilation passage, which is for supplying blow-by gas to an intake passage of an internal combustion engine, and a positive crankcase ventilation valve, which is for regulating the flow rate of blow-by gas in the positive crankcase ventilation passage, the abnormality diagnosis device comprising:

• a determination unit that varies a control amount of the positive crankcase ventilation valve to determine the occurrence of an abnormality in at least either one of the positive crankcase ventilation passage and the positive crankcase ventilation valve, wherein the determination unit performs an abnormality diagnosis in a first determination mode when a re-circulated fuel amount, which is the amount of fuel components in the blow-by gas, is less than a reference amount and in a second determination mode when the re-circulated fuel amount is greater than the reference amount, wherein the determination unit sets a varying amount of the control amount of the positive crankcase ventilation valve in the second determination mode to be smaller than that of the control amount of the positive crankcase ventilation valve in the first determination mode.