ACDelco GM Original Equipment NOx (Nitrogen Oxide) Sensors are exhaust gas sensors that detect the nitrogen oxide content of exhaust from diesel engines, and are GM-recommended replacements for your vehicle's original components. The information from these sensors is used by the engine control module (ECM) to adjust various parameters to help reduce harmful emissions. These original equipment nitrogen oxide sensors have been manufactured to fit your GM vehicle, providing the same performance, durability, and service life you expect from General Motors.