A Volkswagen Jetta two valve saloon with a mileage of about 120 thousand km and manual transmission. When the vehicle inspecting station inspecting the vehicle, it can not pass the tail gas detection, and there is no abnormal phenomenon when driving. Fault diagnosis: using the decoder to store the fault codes of the mixed steam, 16825, accidental, and evaporative emission control system flow fault; 16995, accidental, brake switch, unclear signal; 16556, occasionally, the first system of fuel adjustment is too strong. After clearing the fault code, the display system is normal. After cleaning the throttle and injector, the data improved, but still exceeded the standard obviously. Inspection found that the high voltage line was broken, and the data slightly improved after replacement. After replacing the new spark plug, it is found that the data in the exhaust does not rise and fall, and the platinum spark plug used in the original car is replaced by the original spark plug. It is doubted that the three way catalytic converter is not working well, adding three yuan catalytic converter soft carrier to detect exhaust gas. After installing the soft carrier, the data can be passed, but near the standard lower limit. Considering that the testing instrument will have some error, for the sake of insurance, it is more to maintain the engine to an ideal state, fundamentally solve the problem of low engine combustion efficiency, high emission, and to reduce oil consumption, so further check. In the process of detecting the tail gas, it is found that the value of CO has been unstable. Compared with other vehicles, the range of high and low changes is larger, and further observation of the change law of oxygen sensor data, no problems are found, and no problems have been found for long-term correction and short-term correction. In the running state, the temperature of the data in the data is observed. The temperature of the engine cold car rises gradually after the engine is started. When it is found to 64, it is no longer rising at about 64 degrees C. Even when the cooling fan begins to turn, the maximum water temperature can only reach 64. Because the general vehicle fan works at about 95 C, it is suspected that the water temperature sensor of the vehicle is damaged, so after the replacement of the water temperature sensor, the operation test is carried out. As time goes on, the water temperature rises to 95 degrees centigrade, and the cooling fan begins to move. From the data flow, the water temperature data is restored to normal and the tail gas is detected again with the tail gas analyzer. The measurement results, as shown in Table 1, are obviously lower than the national standard. After passing the car, the car goes to the testing station to inspect the vehicle, and the exhaust gas passes smoothly. Maintenance summary: 1. the fault of the car is caused by a variety of reasons, of which the water temperature sensor parameter deterioration is the main cause of the tail gas emission exceeding the standard, because there is no indication of the fault code, it should be a difficult fault. Because the data provided by the tail gas analyzer in the maintenance work indicated the direction for our diagnosis, we can quickly reduce the fault range and eliminate the difficult fault. 2. because the water temperature sensor can not reflect the working temperature of the engine, the time of the injection time of the engine is too long and the mixed steam is too strong and the CO value in the exhaust is rising. If we do not carefully observe the range of the change of the CO value in the exhaust, and the reflection of the water temperature sensor, it is possible to miss the cause of the failure. . If the water temperature sensor is completely damaged, the engine computer will store the corresponding fault code, but more easily found, so the car fault is in the tail gas analyzer and decoder, combined with the staff's careful analysis, and finally found the cause of the failure. It not only makes the engine exhaust meet the national standard, but also reduces the fuel consumption of the engine, while protecting the environment at the same time saves the car owners a lot of money. 3. in the process of repairing the tail gas, many cars have been found, and it is difficult to find the driver in the process of driving, which not only increases the cost of vehicle use, but also causes environmental pollution. Therefore, as an instrument to test the combustion efficiency of the engine, the exhaust gas analyzer is a completely reasonable new idea. It allows the maintenance personnel to quickly understand the combustion efficiency of the engine and make some maintenance data available. Comment: I compare the table 1 with the hospital inspection report. The form is exactly the same, but it lacks the last column "reference range". In the hospital checklist, the computer program compares the side data with the reference range and automatically rises to the back of the test data to represent the higher or lower limits. The author of this article will agree that car repair and medical treatment are different ways of things. People who go to hospital often have experience, doctors will start a series of checklists according to the condition of the disease. Then, according to the results of the examination, they prescribe medicine prescription or make a diagnosis and treatment plan. The red arrow in Table 1 is added by me. I just made a chain ratio, because no reference range could not make the same year. The second column data in Table 1 is much lower than that in the first column, because it is not measured by the same equipment and the same operator. The third column of data indicates that the data of the fuel injector is not dropping or rising after injection, indicating that the slight plugging of the injector has been dredged. Since then, the author has made three repairs to reduce HC and CO. It is also seen from table 1 that CO2 increases with the decrease of HC and CO, which is the manifestation of harmful gases transforming into harmless gases. A suggestion for this article is put forward: add a row of "seepage test scope" at the end of Table 1 to make the data normal.