With the rapid development of automobile technology, electronic technology has been widely used in automobiles. Since 1980s, automobiles equipped with electronic fuel injection system, electronic ignition system, electronic anti-lock braking system and electronic automatic transmission controlled by microcomputer (ECU) have become the mainstream and direction of automobile industry development. In order to control tail gas emission and save energy, in May of 20001year, China issued a law prohibiting the sale of cars and buses with carburetors with less than 6 seats in 47 major cities. This will play a positive role in promoting the development of China's automobile industry, and also put forward higher requirements for maintenance personnel. Based on the practical experience of daily maintenance of electronically controlled vehicles, I talk about some diagnosis and maintenance skills. Electronic control system 1 maintenance skills. Electronic controller (ECU) is a precise device. Although many failures may be related to ECU, its failure rate is very low, so don't dispose of ECU easily, let alone open its cover casually. 2. Open circuit or poor contact is a common fault of electronic control system. Except for some faults such as broken wires and loose connectors, it is necessary to detect the voltage and resistance of relevant measuring points with high impedance multimeter to determine the fault location, and it is not possible to check whether the line is on or off by scraping fire. Because when the fire is scraped, the instantaneous voltage generated by the self-inductance coil in the circuit will breakdown the electronic components. 3. When the ignition switch is turned on, don't disconnect any electrical equipment, so as to avoid the induced electromotive force generated in the circuit from damaging electronic components. When disconnecting the battery, you must pay attention to the following points: ① The ignition switch must be turned off; ② Check whether the self-diagnosis fault code exists; ③ Remember the password of audio equipment with anti-theft code. 4. After the battery is disconnected and reassembled, if the working condition of the engine is worse than before, don't replace the parts casually, because this situation may be due to the elimination of the "learning correction memory" of E-Cu after the battery is disconnected. When the engine runs for a period of time, the ECU will automatically establish a correction memory, and the bad working conditions of the engine will automatically disappear. 5. When repairing the vehicle by arc welding, be sure to disconnect the electronic control unit from the battery. If welding repair is carried out near the ECU, the ECU box should be removed. Maintenance and diagnosis skills of fuel injection system 1. For electronically controlled fuel injection system, the influence of air leakage in intake system on engine work is far greater than that of carburetor truck. Because in the electronically controlled fuel injection engine, the air leakage is not measured by air flowmeter, which has a great influence on the air-fuel ratio. Therefore, when the engine fails, check whether the air flowmeter, throttle body, auxiliary air valve, idle speed stabilizing valve and exhaust gas recirculation valve are loose, and whether the air hose and its connector are damaged or leaked. 2. After the engine is turned off, there is still a certain pressure of fuel in the fuel pipe, so when disassembling the fuel pipe, it is necessary to prevent the fuel from spraying out and causing danger. 3. The gasket in the tubing is disposable, so it should be replaced again during assembly and cannot be reused. 4. When installing the fuel injector, be careful not to damage the newly replaced O-ring, so as not to affect the sealing performance of the fuel injector. When installing, oil should be used to lubricate the O-ring first, not oil and gear oil. 5. When checking the fuel injection performance of the fuel injector, be sure to know whether the fuel injector is of high resistance type or low resistance type. The resistance of high resistance type is generally 12 ~ 14 ohm, which can be directly connected to the battery to test the fuel injection performance of the injector. However, the resistance of the electromagnetic coil of low-resistance fuel injector is generally only 2 ~ 3 ohms. If it is directly connected to the battery, the fuel injector will be burnt out due to excessive current, so a special connector must be used to connect with the battery. If ordinary wires are used, an 8 ~ 10 ohm resistor should be connected in series. 6. The air flow sensor is a precision component, which has a great influence on the working performance of the engine. When disassembling the air flowmeter, handle it with care and do not disassemble it, so as not to damage or affect its detection accuracy. When cleaning the air flowmeter, do not clean it with water or cleaning solution. 7. The adjusting screw on the air flowmeter is used to adjust the carbon monoxide content at idle speed. Under normal circumstances, it should not be moved. Improper adjustment will lead to a decrease in engine power and an increase in fuel consumption. 8. After long-term use, the performance of the water temperature sensor will change, making the water temperature signal wrong, which will adversely affect the fuel injection, ignition time and the work of the fuel pump. However, the change of performance parameters of water temperature sensor (not short circuit or open circuit) is often not recognized by self-diagnosis system. Therefore, when the engine works abnormally (such as unable to start, unstable idle speed, increased fuel consumption, etc.). ), and the fault self-diagnosis system does not prompt the fault code of the water temperature sensor. Don't ignore the inspection of the water temperature sensor. 9. When overhauling the oxygen sensor, be careful not to let the oxygen sensor fall and collide with other objects. When replacing, be sure to smear the thread with a special anti-sticking brush to avoid falling off.