Patent attributes
An exhaust purification catalyst diagnosis device for diagnosing a degree of performance degradation of a NOx catalyst, which is provided in an exhaust system of an engine for exhaust purification, has a program that determines whether temperature of the NOx catalyst is within a predetermined diagnosis permission range before catalyst diagnosis processing and a program that controls the temperature of the NOx catalyst into the diagnosis permission range before the catalyst diagnosis processing if it is determined that the temperature of the NOx catalyst is outside the diagnosis permission range. Thus, the exhaust purification catalyst diagnosis device can perform the catalyst diagnosis processing frequently with high reliability and high accuracy, while maintaining suitable emission.
