Abstract: An engine emissions control system may include an electronic control module and a nitrogen oxide sensor in communication with the electronic control module. The nitrogen oxide sensor may be mounted on an exhaust system of an engine and may be configured to provide the electronic control module with feedback indicative of an actual level of nitrogen oxide in an exhaust stream flowing through the exhaust system. The engine emissions control system may also include an engine parameter adjustment assembly controlled by the electronic control module. The electronic control module may automatically actuate the engine parameter adjustment assembly to adjust an engine flow until the actual level of nitrogen oxide reaches a desired level of nitrogen oxide.