Exhaust gas purification system for internal combustion engine and exhaust gas purification method therefor

摘要

If an exhaust throttle valve changes to ON state from OFF state under a filter regeneration control condition for regenerating a PM filter, a differential pressure sensor detects a change of a differential pressure following an operation of the exhaust throttle valve. An increase in an exhaust backpressure is calculated based upon the change in the differential pressure. If the increase in the exhaust backpressure is lower than a predetermined value, the operation of the exhaust throttle valve is determined to be malfunctioning.