| abstract |
This invention provides an apparatus for diagnosing the deterioration of an NOx catalyst. In this apparatus, NOx is supplied, to an occlusion/reduction-type NOx catalyst, in such an amount that a criteria catalyst, which is in a boundary between a deteriorated state and a normal state, can occlude. Thereafter, a reducing agent in an amount corresponding to the NOx amount is supplied by rich spike. The level of deterioration of the NOx catalyst is determined based on the output of an NOx sensor. In this apparatus, since the deterioration is determined based on only the level of the output of the NOx sensor, the diagnosis of deterioration can be carried out with high accuracy. Further, since any excess reducing agent is not supplied during a period in which the catalyst is normal, and, thus, a deterioration in fuel consumption can be prevented. |