Abstract: A method for an engine employing an after-treatment (AT) system with an AT device for treating an engine exhaust gas includes detecting an actual concentration of a pollutant in the exhaust gas upstream of the AT device. The method additionally includes treating the exhaust gas via the AT device and directing the treated gas to an exhaust gas passage. The method also includes recirculating a portion of the treated exhaust gas from the exhaust gas passage to the engine's intake passage and determining efficiency of the AT device, after recirculating the portion of the treated exhaust gas, using the detected actual pollutant concentration. Furthermore, the method includes maintaining operation of the AT system when the determined AT device efficiency is at or above a predetermined value and activating a sensory signal indicative of the AT device having malfunctioned when the determined AT device efficiency is below the predetermined value.

Abstract: A method for an engine employing an after-treatment (AT) system with an AT device for treating an engine exhaust gas includes detecting an actual concentration of a pollutant in the exhaust gas upstream of the AT device. The method additionally includes treating the exhaust gas via the AT device and directing the treated gas to an exhaust gas passage. The method also includes recirculating a portion of the treated exhaust gas from the exhaust gas passage to the engine's intake passage and determining efficiency of the AT device, after recirculating the portion of the treated exhaust gas, using the detected actual pollutant concentration. Furthermore, the method includes maintaining operation of the AT system when the determined AT device efficiency is at or above a predetermined value and activating a sensory signal indicative of the AT device having malfunctioned when the determined AT device efficiency is below the predetermined value.