an emissions control method may include operating a hybrid vehicle in a first mode during which a combustion engine is off and an electric motor powers propulsion of the vehicle . an electrically heated catalyst may be energized during the first mode . the method may further include determining an operating temperature of an additional catalyst in communication with exhaust gas from the combustion engine and operating the vehicle in a second mode after the first mode during which the engine powers propulsion of the vehicle . the engine may operate in a catalyst combustion mode during the second mode when the operating temperature is below a first predetermined limit . the catalyst combustion mode may include operating the engine at an air - fuel ratio of less than stoichiometry and injecting air into exhaust gas from the engine at a location before the additional catalyst to create an exothermic reaction within the additional catalyst .