ABNORMALITY DIAGNOSTIS APPARATUS FOR EXHAUST PURIFICATION APPARATUS

An abnormality diagnosis apparatus includes: an exhaust gas purification apparatus arranged in an exhaust passage of an internal combustion engine and including a selective catalytic reduction catalyst; a supply apparatus supplying an additive such as ammonia to the exhaust gas purification apparatus; an EGR apparatus recirculating a part of exhaust gas from the exhaust passage at a downstream side of a position of supplying the additive to an intake passage; calculating means for calculating a NO x inflow amount into the exhaust gas purification apparatus using a parameter indicating an operating state of the internal combustion engine; diagnosing means for diagnosing an abnormality in the exhaust gas purification apparatus using the calculated NO x inflow amount as a parameter; and correcting means for, when a part of the exhaust gas is recirculated, increasingly correcting the calculated NO x inflow amount in accordance with an amount of the additive to be recirculated together with exhaust gas.