a vehicle has an engine , an exhaust aftertreatment system , an electric machine , and a controller configured to , in response to an actual engine torque output being less than an inferred engine torque , shut down the engine . a vehicle has an engine , an exhaust aftertreatment system , an electric machine , and a controller configured to , in response to an actual engine torque output being less than a first threshold and a torque request to the engine being greater than a second threshold , set a diagnostic code . a method includes receiving an actual engine torque output , receiving an engine torque request , and shutting down the engine when the actual engine torque output is less than a first threshold and the engine torque request is greater than a second threshold for a predetermined time period to limit temperature increase of a catalyst .