Abstract: If the amount of fuel added to exhaust gas becomes excessive as a result of an abnormality of an addition agent supply unit (60), the air-fuel ratio of exhaust as decreases. If an exhaust gas air-fuel ratio obtained from a value output from an A/F sensor (4) remains equal to or smaller than a predetermined value for a predetermined period, an ECU (2) determines that an addition agent supply unit (60) is abnormal. Upon detection of an abnormality of the addition agent supply unit (60), the ECU (2) incrteases an amount of EGR gas recirculated to the intake side by an EGR unit (40), reduces an amount of fuel injection from injectors (11), and restricts an operational state of an engine body (10) to a low-speed/low-load state. Also, the ECU (2) turns a warning lamp (7) on, warns a driver of the abnormality of the addition agent supply unit (60), and makes it possible to pull a vehicle over safely.

Abstract: If the amount of fuel added to exhaust gas becomes excessive as a result of an abnormality of an addition agent supply unit (60), the air-fuel ratio of exhaust as decreases. If an exhaust gas air-fuel ratio obtained from a value output from an A/F sensor (4) remains equal to or smaller than a predetermined value for a predetermined period, an ECU (2) determines that an addition agent supply unit (60) is abnormal. Upon detection of an abnormality of the addition agent supply unit (60), the ECU (2) incrteases an amount of EGR gas recirculated to the intake side by an EGR unit (40), reduces an amount of fuel injection from injectors (11), and restricts an operational state of an engine body (10) to a low-speed/low-load state. Also, the ECU (2) turns a warning lamp (7) on, warns a driver of the abnormality of the addition agent supply unit (60), and makes it possible to pull a vehicle over safely.