This NOx sensor monitors the concentration of nitrogen oxides in the exhaust stream of the host tractor. It sends a signal to the engine control unit, which adjusts the selective catalytic reduction (SCR) system to maintain the correct dosing of diesel exhaust fluid. A failing sensor causes the SCR system to operate in a reduced-efficiency mode, often triggering a warning light and a drop in engine power. This component is manufactured to the original sensor calibration, preserving the response curve that the ECU expects for accurate emissions control.