Oxygen sensors are essential components in engines that use three-way catalytic converters to reduce exhaust pollution. Due to the fact that once the air-fuel ratio of the mixture deviates from the theoretical air-fuel ratio, the purification ability of the ternary catalyst for CO, HC, and NOx will sharply decrease. Therefore, an oxygen sensor is installed in the exhaust pipe to detect the concentration of oxygen in the exhaust and send a feedback signal to the ECU. The ECU then controls the increase or decrease of the fuel injection amount of the injector, thereby controlling the air-fuel ratio of the mixture near the theoretical value.