REAGENT DOSER DIAGNOSTIC METHOD

A method is disclosed for determining or diagnosing a reagent dosing system failure to provide sufficient reagent to an exhaust aftertreatment system that includes an SCR catalyst to satisfy a reagent dosing command. The method comprisis: determining a quantity of a reagent to inject with a dosing system over a dosing cycle to treat an exhaust gas in an exhaust system that includes a selective catalytic reduction catalyst, wherein the dosing cycle includes a plurality of dosing periods and a doser on-time and a doser off-time within each dosing period, wherein a predetermined portion of the quantity of the reagent is injected during the dosing on-time of each dosing period; operating the dosing system to inject the quantity of the reagent into the exhaust system during the dosing cycle, wherein operating the dosing system includes controlling a pump of the dosing system with pressure feedback control to maintain an operating pressure of the dosing system when the injector is opened; identifying a diagnostic dosing period from the dosing periods in the dosing cycle; during the diagnostic time period, suspending pressure feedback control of the pump while maintaining a speed of the pump; measuring a pressure drop of the dosing system downstream of the pump during the doser on-time of the diagnostic dosing period; and determining a fault condition of the dosing system in providing the quantity of the reagent in response to the pressure drop measured during the diagnostic dosing period.