SELECTIVE CATALYTIC REDUCTION FAULT DETECTION

Technical solutions are described for selective catalytic reduction diagnosis in an emissions control system or an exhaust system used for treating exhaust gas, such as in a motor vehicle including an internal combustion engine. An example emissions control system includes a selective catalytic reduction (SCR) device. The emissions control system further includes a controller that is performs SCR fault diagnosis. The SCR fault diagnosis includes computing a plurality of estimated NH3 storage capacity values (Θ) of an SCR catalyst of the SCR device. The diagnosis further includes determining a diagnostic parameter of the SCR device using the plurality of estimated NH3 storage capacity values.