MALFUNCTION DIAGNOSIS DEVICE FOR EXHAUST-GAS PURIFICATION DEVICE

摘要

An abnormality diagnosis apparatus for an exhaust gas purification apparatus including a selective catalytic reduction NOx catalyst (SCR catalyst) and a sensor which detects NOx and ammonia in exhaust gas flowing out from the NOx catalyst and at which NOx and ammonia react with each other. The abnormality diagnosis apparatus calculates, based on concentrations of NOx and ammonia which flow out from the SCR catalyst, an amount of decline in output of the sensor due to a reaction between NOx and ammonia at the sensor, and performs an abnormality diagnosis of the SCR catalyst based on the calculated amount of decline in output of the sensor.