Abstract: Methods and apparatuses for monitoring an oxidation catalyst in a vehicle exhaust system include a diesel internal combustion engine with an exhaust system that has an EGR, a DOC/DPF downstream from the EGR, an SCR catalyst downstream of the DOC/DPF, a first NOx sensor located upstream of the DOC/DPF, and a second NOx sensor located downstream of the SCR catalyst. A monitoring cycle of the exhaust system during operation of the diesel ICE includes executing a DPF regeneration event, shutting off the EGR, terminating urea dosing to the SCR catalyst, emptying NH3 storage in the SCR catalyst, and intrusively maintaining the temperature of the DOC/DPF within a predetermined temperature range. Readings from the first NOx sensor and the second NOx sensor allow for a ratio between first NOx sensor readings and second NOx sensor readings, the ratio providing an indication as to whether or not the DOC/DPF is failing or operating properly.

Abstract: An exhaust diagnostic system. The system includes a diesel engine having an exhaust system with a diesel particulate filter (DPF), a diesel oxidation catalyst (DOC), a selective catalytic reduction (SCR) catalyst, a first NOx sensor located upstream of the SCR catalyst and a second NOx sensor located downstream of the SCR catalyst. In addition, an engine control unit (ECU) is in electronic communication with the first NOx sensor and the second NOx sensor. An SCR coordinator can be included and be configured to execute a non-intrusive SCR deNOx efficiency test, an intrusive SCR/DOC deNOx efficiency test and an intrusive DOC non-methane hydrocarbon (NMHC) conversion efficiency test on the exhaust system. As a result of the conversion efficiency tests, a distinction can be made as to whether the SCR catalyst or DOC is failing.

Abstract: An exhaust diagnostic system. The system includes a diesel engine having an exhaust system with a diesel particulate filter (DPF), a diesel oxidation catalyst (DOC), a selective catalytic reduction (SCR) catalyst, a first NOx sensor located upstream of the SCR catalyst and a second NOx sensor located downstream of the SCR catalyst. In addition, an engine control unit (ECU) is in electronic communication with the first NOx sensor and the second NOx sensor. An SCR coordinator can be included and be configured to execute a non-intrusive SCR deNOx efficiency test, an intrusive SCR/DOC deNOx efficiency test and an intrusive DOC non-methane hydrocarbon (NMHC) conversion efficiency test on the exhaust system. As a result of the conversion efficiency tests, a distinction can be made as to whether the SCR catalyst or DOC is failing.