Troubleshooting ideas for the most popular automot

The characteristics of modern automotive electrical and electronic equipment are mainly reflected in function Intensification (combination), control electronization and connection standardization. When analyzing the fault of electronic circuit, because it is always associated with relevant electrical equipment, we must understand the general characteristics of electrical and electronic equipment. Before analyzing and overhauling electronic circuits, we should pay attention to the following features: cars are generally equipped with main power switches, which are mostly electromagnetic. There are many places on the car equipped with fusible wires. After the completion of the project, it will constitute the world's first fully automatic solid-state lithium-ion battery production line to protect the harness, rather than protect a specific electrical appliance. The difference between it and fuse is that its fusing reaction is slow and it is in the form of wire. After the protective fuse is blown for some reason, it cannot be found as easily as the fuse. Some even in the harness, we should pay more attention when analyzing the fault. Except for a few cases, all imported cars are connected by single wire system, and the metal structure of the car body is used as another common wire, and all electrical appliances are connected to it in the form of "grounding". In principle, all electrical appliances used are low-voltage and high current devices. Even the same model from the same manufacturer will have some improvements due to different delivery years.: Top experts recruit four money saving strategies to solve the problem of vehicle maintenance and repair, saving the cost of vehicle maintenance and repair

the characteristics of electrical faults on modern cars can be linked to their use characteristics one by one. Generally, electronic components are very sensitive to overvoltage and temperature. For example, the PN junction of transistors is prone to overvoltage breakdown, the leakage of electrolytic capacitors also increases when the temperature rises, and silicon controlled components are sensitive to overcurrent. These fault characteristics are summarized as follows:

a. component breakdown. Breakdown includes over-voltage breakdown or over-current, thermal breakdown caused by overheating, etc. Breakdown sometimes takes the form of short circuit, and sometimes takes the form of open circuit. Overvoltage and overcurrent breakdown caused by circuit failure are often unrecoverable

b. component aging or performance degradation. This includes many aspects, such as the capacity of the capacitor decreases, the insulation resistance decreases, the leakage of the transistor increases, the resistance value of the resistance changes, the resistance value of the adjustable resistance cannot change continuously, the relay contact ablation, etc. Components such as relays often fail to adjust the initial action current due to insulation aging, coil burnout, inter turn short circuit, contact jitter

c. line fault. Such faults include poor insulation, short circuit, bypass, etc. caused by loose wiring, poor contact, humidity, corrosion, etc. Such faults are generally independent of components

key points for troubleshooting the above faults:

a. analyze the circuit principle and clarify the overall circuit and connection. Once you encounter unfamiliar models and lines, you often have to do it yourself, analyze the circuit principle, and even map the necessary circuit diagrams. Therefore, the maintenance of automotive electronic circuits will involve circuit analysis methods

b. eliminate them one by one from the outside to the inside, and finally determine their technical status. For many reasons such as performance requirements and technical protection, many electronic circuits in cars often use non removable packaging, such as thick film packaged regulators, solid sealed ignition circuits, etc. If a fault may involve its interior, it is often difficult to judge. It needs to be eliminated from the periphery one by one, and finally determine whether they are damaged

c. pay attention to the feasibility of component substitution. For example, although the electronic circuits on some imported cars can be disassembled, they often lack the replacement of discrete components of the same model, so it is often necessary to try to replace them with domestic or other imported components. This involves the feasibility of component replacement

d. it is not allowed to use the "fire test" method to identify the fault location and cause. In terms of maintenance methods, traditional automobile electrical faults often can be identified one by one by means of "fire test". Although this method is not very safe and reliable, and has certain harm to the battery, it is still feasible in the traditional maintenance method. This method is not allowed on imported cars equipped with electronic circuits. Because the "fire test" produces overcurrent, it will bring unexpected damage to some circuits or components. Therefore, when repairing imported automotive electrical appliances, we must use some instruments and tools to carry out in a certain way

e. prevent current overload. It is not allowed to use the low resistance ohm gear below rx100 of ohmmeter and multimeter to detect low-power transistors, so as to avoid current overload and damage

f. be careful of electrostatic breakdown triode. When replacing the triode, the base should be connected first; When disassembling, the base should be disassembled finally. For metal oxide semiconductor tubes, electrostatic breakdown should be considered. When welding, unplug the soldering iron plug from the power supply. Prevent the soldering iron from scalding the components. When removing and installing components, cut off the power supply. Unless otherwise specified, the distance between the component pin and the solder joint should be more than 10mm to prevent the soldering iron from burning the component. An electric soldering iron with constant temperature or power less than 75W should be used

the electronic control system of modern vehicles, like other assemblies and components, works under complex and variable conditions. In addition, due to design and manufacturing reasons, after a certain mileage, there will inevitably be one or another problems, that is, circuit failure will lead to local or overall loss of working capacity. In the repair process of automotive electrical equipment, the determination of whether electrical equipment can be applied again and which troubleshooting method to choose should be based on the performance and degree of damage of electrical equipment. When repairing according to the process route of electrical equipment repair in the factory, the overall of various faults forming the repair route plays an important role in the selection of repair methods and the determination of repair procedures. Therefore, we should not only study the distribution of electrical equipment damage, but also make clear the statistical law of the actual combination of various faults, and compile the repair process route of electrical equipment according to certain principles

the main task of electrical equipment repair is to use the remaining durability of electrical equipment to ensure the economic and effective repair of automotive electrical appliances and the restoration of their reliability. There are great differences in the technical status of electrical equipment, so the repair expenses of electrical equipment are also different. At this time, this situation may occur, that is, it is not cost-effective to repair individual fault combinations. Therefore, the economic rationality of electrical appliance repair is the main feature of the collection of electrical appliance conditions divided into various repair process routes. The purpose of the classification of parts to be repaired is to form an electrical repair route with common characteristics in both process problems and their solutions. Therefore, along with the features describing the condition of electrical appliances, the features that can distinguish all faults and their combinations into process similar categories should be cited. This distinction should be based on the commonality of the main repair procedures, protection and maintenance, and the commonality of the electrical equipment used. When identifying parts, we should consider the rationality of their repair, which will complicate the work of the inspection and classification section. Because inspectors must not only remember all the fault combinations, but also forget the price standard of scrapping electrical equipment. When classifying the fault combination categories according to the repair route, the most obvious distinguishing features between various faults should be cited. From the point of view of organizing the repair of electrical equipment from the process specification, it is helpful to merge the various fault combinations that have been found into the category of a few typical process routes, which greatly simplifies the content of selecting the best scheme of the process route, which is the analog sensor before operation and the digital sensor after operation. According to certain principles, all the fault combinations should be divided into reasonable categories and the best scheme should be selected in order to obtain the maximum benefit of electrical equipment repair

circuit faults can be divided into gradual faults and sudden faults according to the time of occurrence. It is difficult to record the gauge distance value on the first side of the progressive fault. The period of occurrence is long, and the degree of fault has a process from light to heavy, from weak to strong. They are mostly caused by friction and wear during the operation of parts, such as a cylinder misfire caused by the wear of the cam of the ignition breaker, and the chamber sweeping of the starter, etc. Sudden faults are mostly caused by short circuit or open circuit of the circuit, such as sudden failure of the headlamp and sudden shutdown of the engine. Circuit faults can be divided into destructive faults and functional faults according to their impact on machine functions. Destructive failure refers to the complete loss of working capacity of electrical assemblies or components due to failure, and the inability to continue working without replacement or overhaul, such as bulb filament burnout, integrated circuit regulator breakdown, generator stator coil burning, etc. Functional failure refers to the non-destructive failure that the electrical apparatus can reduce but not completely lose its working capacity. Its function can be restored after adjustment or local maintenance, such as the contact ablation of the ignition breaker, too large or too small gap, etc

friction, wear or fatigue of machinery in normal operation. For example, if the rotor shaft and shaft sleeve of the starter are lubricated with grease, the driving pinion and the flywheel ring gear cannot mesh correctly due to wear, and the top gear hits the gear, resulting in short circuit or open circuit, poor contact or leakage in the circuit. If the generator is overloaded and the rectifier diode is short circuited; Overvoltage causes the voltage regulator switch tube to break down and open circuit, and the contact is ablated without conducting electricity; The capacitor breaks down and cannot store charge, etc. The electrical components in the circuit rely on the mechanical structure, which leads to poor circuit contact due to mechanical wear, looseness or insufficient spring force. When cars are used in different regions, climates and topographical conditions, various faults often occur. For example, the increase of lubricating oil viscosity and starting resistance at low temperature will cause early damage to the battery; Plastic parts and insulating materials of automotive electrical appliances will age due to high temperature; Acid rain will corrode auto parts. The illegal driving operation does not maintain, clean and adjust as required, resulting in wear and tear of parts; Unreasonable design, poor manufacturing and poor assembly of parts will lead to the failure of circuit components

although the types and phenomena of line faults are diverse, their essence can be divided into mechanical faults, electrical faults and electromechanical comprehensive faults. These three types of faults are different from and related to each other, and cannot be viewed in isolation. For example, bearing wear causes the generator and starter to sweep the bore; The switch cannot be positioned and the spring fails, resulting in poor contact of the contact; The shaft is bent, causing excessive runout, etc. Mechanical failure will cause electrical failure if it lasts for a certain period of time, such as short circuit of motor armature coil caused by bore sweeping, too large contact gap and failure to connect the primary circuit of ignition, etc

electrical faults are mainly caused by short circuit, open circuit, poor contact or leakage in the circuit. For example, the overload of the generator causes the short circuit of the rectifier diode, the overvoltage causes the breakdown and open circuit of the last stage switch tube of the voltage regulator, the contact is ablated and does not conduct electricity, the capacitor breaks down and cannot store charge, the inductor coil is short circuited between turns or layers or grounded with the body, the breakdown and leakage of the high-voltage insulating element, the loosening or corrosion of the battery pole causes non conduction, the power supply voltage is too high and too low, the magnetic flux of the magnetic element is weakened or enhanced, and the circuit parameters such as frequency Phase variation occurs. The fundamental solution to the problem of poor circuit contact caused by mechanical reasons is to restore the integrity of the mechanical structure. When judging circuit faults, it is not enough for people to have time to focus on the circuit or circuit diagram. Simply paying attention to the circuit and ignoring the mechanical structure will lead to the recurrence of mechanical and electrical comprehensive faults if they are not handled properly. in order to