The zirconia oxygen sensor provides a feedback signal for stoichiometric air-fuel ratio (A/F) control of an engine. Precise control of A/F within ±1% of the stoichiometric point is required for effective operation of a three-way catalyst. Since the ultimate accuracy of the closed loop control system directly depends on the accuracy of the oxygen sensor, the present investigation was undertaken to quantify factors affecting sensor accuracy. Measurements were made of the relative importance of engine exhaust flow and exhaust temperature on the voltage output of the zirconia oxygen sensor.A test engine was run on a dynamometer at fixed speed and load. A special arrangement on the exhaust pipe permitted independent adjustment of exhaust flow and exhaust temperature. Coefficients for the differential changes in sensor voltage due to changes of engine air-fuel ratio, exhaust flow, and exhaust temperature were determined.