Patent ID: 6968677

Claim:
An exhaust emission control apparatus for an internal combustion engine, comprising: an exhaust flow control device that suppresses exhaust flow so as to reduce harmful substances in exhaust; an engine speed detecting device that detects an engine speed; a fuel quantity control device that controls a fuel quantity contributed to output torque; an ignition timing control device that controls an ignition timing; an intake air volume control device that controls an intake air volume; and a failure diagnostic device that fixes three parameters selected from the group consisting of the engine speed detected by said engine speed detecting device, the fuel quantity controlled by said fuel quantity control device, the ignition timing controlled by said ignition timing control device, and the intake air volume controlled by said intake air volume control device at respective predetermined values and finds values of a remaining one parameter irrespective of a degree to which the exhaust flow is suppressed by said exhaust flow control device, and compares the values of the remaining one parameter with each other to determine whether said exhaust flow control device has failed.