Catalyst deterioration diagnosis system and method for internal combustion engine

摘要

A catalyst deterioration diagnosis system performs a diagnosis of deterioration of the oxidation catalyst based on a high-temperature-inflow-condition exhaust gas temperature and a low-temperature-inflow-condition exhaust gas temperature. The high-temperature-inflow-condition exhaust gas temperature is a temperature detected by a temperature sensor while the temperature of the exhaust gas that flows into the oxidation catalyst is in a high temperature region H while the reducing agent is supplied from the reducing agent supply means into the exhaust gas that flows into the oxidation catalyst. The low-temperature-inflow-condition exhaust gas temperature is a temperature detected by the temperature sensor while the temperature of the exhaust gas that flows into the oxidation catalyst is in a low temperature region L while the reducing agent is supplied from a reducing agent supply means into the exhaust gas that flows into the oxidation catalyst.