Nowadays, the design of the car is getting more and more advanced. With the coming, the fault repair technology of the car has to be improved. Electronic fuel injection systems controlled by microcomputers (ECUs), electronic ignition systems, electronically controlled anti-lock systems, and electronically controlled automatic transmission systems have become the mainstream of the sedan industry. In multi-performance, high-tech automotive products, maintenance personnel skills put forward higher requirements. Today, Xiaobian talks about the common troubleshooting and diagnostic techniques in automotive electronic control systems.
(1) Electronic controller (ECU) is a precision device. Although many fault phenomena may be related to the ECU, the failure rate is very low, so do not dispose of the ECU easily, and do not open the ECU cover casually.
(2) During maintenance, pay attention to the lock type of the harness connector of each model, and do not blindly force hard pull. To be inserted into the position during installation, the lock should be locked.
(3) Circuit open circuit or poor contact is a common fault of electronic control system. In addition to some lines disconnected, plug connectors and other faults can be checked by visual method. High-impedance multimeter must be used to detect the voltage and resistance of the measuring point. Judging the fault location, you can't use the method of scraping to check whether the line is on or off. Because the instantaneous voltage generated by the self-inductive coil in the circuit breaks down the electronic component during the scraping.
(4) When the ignition switch is turned on, do not disconnect any electrical equipment to prevent the induced electromotive force generated in the circuit from damaging the electronic components. When disconnecting the battery, pay attention to the following points:
1 The ignition switch must be turned off; 2 Check if the self-diagnosis fault code exists; 3 Remember the password of the audio equipment with the anti-theft code.
(5) After the battery is disconnected and reassembled, if the engine working condition is not as good as before, do not replace the parts casually, because this situation may be caused by the elimination of the “learning correction memory†of the ECU after the battery is disconnected. After the engine is running for a period of time, after the ECU automatically establishes the correction memory, the engine malfunction will automatically disappear.
2, fuel injection system maintenance diagnostic skills(1) For the electronically controlled fuel injection system, the impact of the air leakage of the intake system on the engine operation is much greater than that of the carburetor type sedan. Because on the electronically controlled fuel injection engine, the air leakage is not measured by the air flow meter, which has a great influence on the air-fuel ratio. Therefore, in the event of engine failure, check the air flow meter, throttle body, auxiliary air valve, idle speed stability valve and exhaust gas recirculation valve for looseness, air hose and its joints for damage or air leakage.
(2) After the engine is turned off, there is still a certain amount of fuel in the oil pipeline, so it is necessary to prevent the fuel from being ejected and dangerous when disassembling the oil pipe.
(3) The sealing gasket in the oil pipeline is disposable. It should be replaced when assembling. Do not reuse it.
(4) When installing the injector, be careful not to damage the newly replaced O-ring to avoid affecting the injector's tightness. When installing, apply oil to lubricate the O-ring first. Do not lubricate with oil and gear oil.
(5) When checking the fuel injection performance of the injector, it must be clear whether the injector is of high resistance type or low resistance type. The high-resistance type resistor is generally 12 to 14 ohms, and can be directly connected to the battery for fuel injector injection performance test. However, the resistance of the low-resistance injector electromagnetic coil is generally only 2 to 3 ohms. If the battery is directly connected to the battery, the injector will be burnt due to excessive current. A special connector must be used to connect the battery. If a normal wire is used, a resistor of 8 to 10 ohms needs to be connected in series.
(6) The air flow sensor is a precision component and has a great influence on the engine performance. When removing the air flow meter, it should be handled gently and do not disassemble the air flow meter to avoid damage or affect its detection accuracy. Do not rinse with water or cleaning solution when cleaning the air flow meter.
(7) The adjustment screw on the air flow meter is used to adjust the content of carbon monoxide at idle speed. Under normal circumstances, it should not be moved. Improper adjustment will cause the engine's power to drop and fuel consumption to increase.
(8) After long-term use of the water temperature sensor, the performance will change, causing an error in the water temperature signal, which will adversely affect fuel injection, ignition time and fuel pump operation. The change in performance parameters of the water temperature sensor (not short circuit or open circuit) is often not recognized by the self-diagnostic system. Therefore, when the engine is not working properly (such as unable to start, idle speed, fuel consumption increase, etc.), and the fault self-diagnosis system does not indicate the water temperature sensor fault code, do not ignore the inspection of the water temperature sensor.
(9) When servicing the oxygen sensor, be careful not to let the oxygen sensor fall and collide with other objects. When replacing, be sure to use a special anti-adhesive brush to apply the thread to avoid difficulty in disassembly next time.
3, electronic control anti-lock system maintenance skills(1) After starting the engine, sometimes a similar impact sound will be heard from the engine compartment. This is the sound of ABS self-test, which is not abnormal.
(2) The electronic control unit of the electronically controlled anti-lock system has a low failure rate. Therefore, most of the malfunctions of the electronic control device are not problems of electronic components, but are caused by poor connection of the wires or contamination of the components. If the fault code indicates that the sensor is faulty, first check whether the contact points of the sensor are in good contact, whether there is rust or the like.
(3) For the anti-lock braking system with accumulator, when the hydraulic system is repaired, the accumulator should first be depressurized to prevent the high-pressure brake fluid from being sprayed and wounded.
(4) Since the normal operation of the brake anti-lock braking system must be based on the integrity of the original braking system, the maintenance of the original braking system should be carried out normally. When replacing the brake pad, unscrew the bleeder screw of the brake caliper before pressing the piston, otherwise the dirt in the cylinder may be pressed into the pipe to cause component failure. The returning oil can also cause the electronic control unit to get the wrong information, and the brake anti-lock system can be protected and closed. If the hydraulic brake system needs to be vented during maintenance or use, follow the procedures specified in the vehicle's instructions for use. Because the deflation procedure with the brake anti-lock brake system and the normal brake system may be somewhat different, the deflation procedure of the original brake system cannot be blindly copied.
4, electronically controlled automatic transmission maintenance skills(1) The characteristic of fault diagnosis of electronically controlled automatic transmission is to first determine whether the fault is in the electronic control part or the mechanical part, or the hydraulic part. If the fault light is on, the fault can be considered in the electronic control part. If the electronic control system is normal, use The oil pressure gauge detects whether the oil pressure of the main oil passage of the automatic transmission is within the normal range. If the oil pressure is normal, the fault is likely to be in the mechanical part.
(2) When the vehicle is being repaired, the ignition switch should be turned off, that is, it should be turned to the “LOCK†position. The electric control system should be overhauled when the negative pole of the battery is disconnected for more than 20 seconds.
(3) When replacing the oil seal, repairing the valve body and the solenoid valve, the transmission oil should be drained as much as possible. When disassembling Nuts and sensors, special tools should be used whenever possible. When installing, tighten it to the specified torque.
(4) The accuracy of the parts of the automatic transmission is relatively high. After the disassembly, various tests cannot be carried out. Only after the comprehensive inspection and repair is completed, the test can be carried out, so it must be thoroughly inspected before disassembly and repair.
(5) When disassembling and repairing the parts of the automatic transmission, it is best to disassemble and repair one component group at a time. After the group is assembled, another group can be repaired to avoid mistakes. All disassembled parts should be cleaned with transmission oil or kerosene. Dry them during assembly and blow the oil passages and oil holes with compressed air. Do not use rags.
(6) Allow at least 15 minutes of immersion in the transmission oil before replacing the new brake and clutch friction plates. All disassembled gaskets and seal rings should be replaced with new ones and should be coated with transmission oil.
(7) When repairing and disassembling the valve body, pay attention to the disassembly and assembly method, so as to prevent the ball valve on the valve body from falling off and not knowing the installation position. The control valves and springs should be carefully disassembled and assembled. Do not touch the surface of the control valve when disassembling.
(8) When the transmission is disassembled and installed on the vehicle, ensure that the torque converter is installed in place and perform necessary inspection and adjustment of the transmission before driving.
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