The three-way catalytic converter is located at the first bulge of the automobile exhaust pipe, and its shape is similar to that of a marching pot. The three-way catalytic converter is installed in the automobile exhaust system and is a very important external purification device in the exhaust system. Three-way catalytic converter is used to purify waste gas, which is installed in the first section of exhaust pipe. If a car has two exhaust pipes, there are two or more three-way catalytic converters. If there is no three-way catalytic converter, the toxic and harmful substances in automobile exhaust will exceed the standard and pollute the environment. There is an oxygen sensor before and after the three-way catalytic converter. The front oxygen sensor is called the front oxygen sensor and the rear oxygen sensor is called the rear oxygen sensor. The main function of the front oxygen sensor is to detect the oxygen content in the exhaust gas. The sensor can feed back the data to the ecu, and the ecu can adjust the air-fuel ratio according to this data. The air-fuel ratio is a very important data for the engine, and the main function of the post-oxygen sensor is to detect whether the three-way catalyst is invalid. If the data fed back by the front oxygen sensor and the rear oxygen sensor are the same, the three-way catalytic converter is invalid. After the fault occurs, the fault light on the dashboard of the car will light up to remind the driver. The meaning of ecu: electronic control unit (ECU), also known as "trip computer" and "vehicle computer". In terms of use, it is a special microcomputer controller for automobiles. Like ordinary computers, it consists of microprocessor (CPU), memory (ROM, RAM), input/output interface (I/O), analog-to-digital converter (A/D) and large-scale integrated circuits such as shaping and driving. To describe it in a simple sentence is "ECU is the brain of a car". Common phenomena after failure: automobile exhaust will smell after the failure of three-way catalyst, and the annual inspection of automobile after the failure of three-way catalyst is unqualified, so it is necessary to replace accessories in time.