The FAW Volkswagen Bora 1.8 car with a mileage of about 143 thousand km. After the car accident, the airbag in the car is detonated, but after the replacement of the two airbag and air bag control unit, the air bag fault warning lamp on the dashboard is often bright and no fault code. Fault diagnosis: after asking the owner, the car does not code the air bag control unit after the replacement of the air bag and air bag control unit, but the FAW Volkswagen has to code after replacing the air bag control unit. The fault diagnosis instrument V. A. G1552 is coded for the new airbag control unit through 1-15-07-12622, but after coding, the vehicle is started and the air bag fault warning lamp on the dashboard still calls the alarm, and the air bag control unit is suspected to have problems. The read control unit is encoded as "12622", and there is no trouble code. Install the old airbag control unit on the vehicle, use V. A. G1552 to enter the human address 15 airbag control unit, read the control unit code as "12622". The query has 3 fault codes: (1) 00595, storage of car crash data; (2) 00588, driver side airbag N95 resistance is too large / occasional; (3) 00589, N131 passenger side airbag resistance is too large / occasional. By comparing the information interface of the two new and old air bag control units, it is found that the first difference between the two airbag control units is that the spare parts are different: the old air bag control unit is 6Q0 909601 ZNA2RBAGVW5006 COD 12622 and WSC00000; the new air bag control unit is 1 C0 909601 ZNA2RGBAGVW5 K43120 COD 00000. WSC00000. After inquiry FAW Volkswagen special maintenance station, the two airbag control unit, although the spare parts number is different, but the newly purchased airbag can be used, but it is only necessary to re code the air bag control unit and make it "12875". The new airbag control unit is installed, the V. A. G1552 is used to code the air bag control unit, and it is coded as "12875", test and troubleshooting. Maintenance summary: the spare parts number of the two air bag control unit is different, and the new control unit code 12622 is wrong at first, which is the cause of the air bag fault warning light alarm. Maintenance review: after changing the control unit of Volkswagen, it is necessary to encode the control unit, because computer manufacturers design a computer, which requires it to be installed in different models, different configurations, and can be used in different countries. Computer manufacturers installed several sets of applications in the control unit. The manufacturer or repair shop used the diagnostic instrument to select a set of programs suitable for this vehicle. After changing the new computer, it will not work correctly without coding or coding. The former maintenance personnel in this case did not have code awareness after replacing computers, making the airbag system still not working. After reading the car, the writer saw that the airbag warning lamp was always bright and realized that the control unit was not coded. There are three channels to obtain COD code, one is to inquire the old control unit (but the old computer code "12622" is mistaken); the two is to consult the data, and the airbag computer in the Bao Lai's Handbook has 23 codes, only there is no code for the Chinese treasure car, and the three is consulting the special service station. The code is "12875". After coding, the airbag works well. The author has a correct diagnosis method and strong coding consciousness, though it has small setbacks, but quickly solved the problem. After discussing this case, we look at the fault diagnosis method of 4S store (including the special service station) and the comprehensive brand repair plant. The maintenance personnel in the 4S shop generally diagnose the fault by the maintenance manual and the manufacturer's technical notification. The maintenance personnel of the comprehensive brand repair plant generally diagnose the fault by experience, because the comprehensive plant is not easy to obtain. Get technical information from the factory and get technical training for a certain vehicle. The two maintenance enterprises have their own characteristics. After the new car is listed, the former can be repaired in large quantities, and the latter can only be maintained until the end of the quality claim period and even a few years. The former is abundant in data and instruments, and the diagnosis process is standardized. The latter lacks data and instruments, and the diagnosis process is not standard. The latter is not without advantages. They can access many kinds of vehicles and gain more maintenance experience. How can a comprehensive brand repair shop get information and make the unfavorable factors favorable? I think it is necessary to set up a technical information room, select personnel with good technical quality and high enthusiasm for work, and to collect all kinds of information such as paper, electronic, CD and so on. The electronic version is best, because it is low cost, easy to maintain and easy to use, but it must be equipped with printers and which page to print. The channels for collecting information are: (1) regular books. (2) technical materials with good printing quality. If it is reproduced information, it is very difficult to see clearly the circuit symbols. (3) all kinds of automobile periodicals, the periodicals are rich in content and many types of cars, but they are not good to find in use. They should be indexed according to the model and system so as to find the one that is needed quickly. (4) raw materials, including paper, CD-ROM, and electronic documents, remember to save the bottom after reading, copy and scan them for later reading. Communicate with peers through telephone, e-mail, QQ group and so on. Internet provides information through search engines, technology forums and auto data websites. Consult 4S shop. For example, when buying spare parts at 4S store, you should ask if the replacement parts are replaced, the key points of installation and adjustment, and the coding of control units. Except for the information that can be read online online with the after-sales service department of the host factory, a variety of model repair plants can also collect the necessary technical information as long as they think more about it.