Features: * Function 1.The front oxygen sensor is to detect the air-fuel ratio of the engine in different working conditions. 2.The rear oxygen sensor is mainly to detect whether the three-way catalytic converter works normally. * 100% test before shipment. * The reduction of harmful emissions. * The increasing of fuel economy. * The improvement of engine performance. * Prevent premature failure of the catalytic converter. Specifications: part number: 234-5029 234-4238 .