Check whether the catalytic converter is damaged during operation and whether it is overheated. After the vehicle is raised, it is observed whether there is a depression on the surface of the catalytic converter, such as obvious dents and scraping, indicating that the carrier of the catalytic converter may be damaged. The mechanical fault diagnosis of automotive catalytic converter can start from the following aspects: 1. Inspection and inspection to check whether the catalytic converter is damaged and whether it is overheated. After the vehicle is raised, it is observed whether there is a depression on the surface of the catalytic converter, such as obvious dents and scraping, indicating that the carrier of the catalytic converter may be damaged. Whether there are serious discoloration spots on the catalytic converter shell or traces of green and purple, is there very obvious dark grey spots in the center of the catalytic converter shield, for example, that the catalytic converter is overheated and needs further examination. With the fist knocking and shaking the catalytic converter, if the sound of a moving object is heard, the internal catalyst carrier is broken and the catalytic converter needs to be replaced. At the same time, check whether there are cracks in the catalytic converter, whether the connections are solid, and whether all kinds of pipes are leaking. If so, they should be dealt with in time. This method is simple and effective, and can quickly check the mechanical faults of catalytic converters. As the catalyst carrier is damaged and spalling and the oil pollution is gathered, the channel of the carrier is blocked easily and the flow resistance is increased. The pressure loss can be measured by measuring the pressure loss. 2, the vacuum test takes the vacuum table to the intake manifold to start the engine, so that it gradually rises to 2500r/min from the idle speed to observe the change of the vacuum table. If the vacuum degree drops, the engine speed is 2500r/min constant, and the vacuum degree reading decreases obviously after that, then the catalytic converter is blocked. Because the blocking of the catalytic converter is a gradual process in the vacuum test, the test is a steady process, and the readings of the vacuum degree will not produce a significant decline. If a catalytic converter is blocked before and after a contrast examination in a catalytic converter, the vacuum degree of the intake manifold will decrease obviously after the catalytic converter is blocked. If the intake manifold vacuum degree falls, it can not be completely explained by the blocking of the catalytic converter. When the engine fuel supply is reduced, the vacuum of the intake manifold will also decrease. Therefore, compared with the vacuum test, the exhaust backpressure test can more accurately reflect the situation of the catalytic converter. The above method can only check the mechanical failure of the catalytic converter, and the performance of the catalytic converter, that is, its conversion efficiency, should be judged by the following examination. 3. The back pressure test plays a hole in the appropriate position of the front end exhaust pipe of the catalytic converter and connects out a pressure gauge to start the engine. At idle speed and 2500r/min, the exhaust backpressure is measured respectively. If the exhaust back pressure does not exceed the limit specified by the engine, the catalyst carrier is not blocked. If the exhaust backpressure exceeds the limit specified by the engine, the exhaust system at the back end of the catalytic converter will be removed and repeated tests are repeated. If the catalytic converter is blocked, the exhaust backpressure will still exceed the limit specified by the engine. If the exhaust back pressure drops, the exhaust system downstream of the muffler or catalytic converter is a problem, and the broken catalyst carrier is detained in the downstream exhaust system, so it is necessary to first make the appearance check to confirm the integrity of the catalyst carrier. The defective exhaust pipe, muffler and catalytic converter can also be judged by measuring the pressure loss before and after. 4. In the normal working state of the catalytic converter, a large amount of reaction heat is produced by the oxidation reaction, so the performance of the catalytic converter can be judged by the temperature difference contrast. Starting the engine, preheating to normal working temperature, maintaining the engine speed around 2500r/min, lifting the vehicle, measuring the temperature of the inlet and outlet of the catalytic converter with a digital thermometer, as close as possible to the catalytic converter. The temperature of the catalytic converter outlet should be at least 10 - 15% higher than the inlet temperature. Most of the normal catalytic converters, the temperature of the catalytic converter outlet is higher than the inlet temperature of 20 ~ 25%. If the vehicle is also installed with the auxiliary catalytic converter before the main catalytic converter, the outlet temperature of the main catalytic converter should be higher than the inlet temperature of 15 ~ 20%. If the outlet temperature is below the range above, the catalytic converter works unnormally and needs to be replaced. If the outlet temperature exceeds the above range, it is indicated that there is an anomaly in the exhaust gas. High concentrations of CO and HC require further examination of the engine itself. Other methods are not scientific to judge the efficiency of the converter by comparing the vehicle emission. Because the emission of automobile is related to the working condition of every system, there are many error factors that can not be excluded. It is not very accurate to check the conversion efficiency of the catalytic converter when the exhaust concentration changes at a cold and hot idle speed. When the cylinder wall is cold and the combustion is not complete, a large number of CO and HC are produced when the cylinder wall is cold. While the engine hot car is idle, the engine is in a closed loop control state because of the improvement of the combustion conditions, and the catalytic converter does not need the role of the catalytic converter, and the exhaust concentration will be greatly reduced. Therefore, this test can not guarantee that the conversion efficiency of the catalytic converter is not good.