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An NOx sensor based on mixed potential was made by laminating YSZ green sheets, on which an NOx sensing electrode, an NOx conversion electrode, a Pt heater, and a pair of thermocouples were printed and sintered. The NOx sensor was redesigned to reduce the number of lead wires from the sensor body. The oxygen sensor in the inner cavity of the sensor was also eliminated to improve controllability and reliability. Sensing characteristics in model gases have demonstrated that NOx concentrations as low as 1 ppm can still be detected by the simplified sensor. Even though the sensor shows a slight interference from HC, overall performance for sensing low levels of NOx in model gases is good. Its performance in exhaust from a stoichiometric engine (λ≦1 ) also shows that this NOx sensor is operable 1 under more realistic conditions.