Car lighting faults, quick troubleshooting and repair methods
Zhang Ning
The car lighting system is a part of the car's electrical appliances. Once a problem occurs, it will seriously affect the driver's driving safety and bring huge safety hazards. Therefore, the lighting system is very important to the entire vehicle. The lighting system includes electrical equipment, control units, circuits, etc. If a fault occurs, it is necessary to diagnose it in time, analyze the cause of the fault, find the fault point, and quickly eliminate and repair it. Specifically, the lighting fault diagnosis method consists of the following links.
1 Learn to find information and obtain learning resources through multiple channels
If you want to do your job well, you must first sharpen your tools. If you want to diagnose and eliminate lighting faults, the relevant preparations must be sufficient, especially the preparation of data. It is necessary to collect information extensively from multiple channels. Among them, commonly used information for fault diagnosis includes configuration tables of faulty models, circuit diagrams, maintenance manuals, typical maintenance cases, etc. Only important information can be organized in advance for easy reference and provide sufficient information for the implementation process of troubleshooting. Only with technical support can we find ideas and methods to solve problems as quickly as possible and save time to the greatest extent. Currently, all major vehicle manufacturers have adopted certain confidentiality measures for the technical data of their models. Only 4S stores and authorized dealers can obtain it directly from the manufacturers. However, in addition to this approach, maintenance personnel can also make full use of the Internet. Nowadays, a large number of auto repair practitioners are active on professional websites, social platforms, and industry forums, sharing and exchanging experiences and information. These are valuable learning opportunities. Resources can be fully utilized to provide a very good reference and bring great convenience to subsequent fault diagnosis.
2 Understand the composition of circuits and read circuit diagrams
First of all, it is necessary to have a detailed and in-depth understanding of the components of the lighting system. The working principle and structure of each electrical component must be well understood. Only by understanding the principle structure can the possible fault points be analyzed. Secondly, you must be familiar with the car circuit diagram. For the normal operation of electrical components, current must pass through. The flow direction and path of the current are the key to understanding the entire vehicle electrical appliances. This information is all reflected in the vehicle circuit diagram.
3 Develop clear and efficient fault diagnosis ideas
3.1 Check the fault phenomenon carefully
During the use of the car, once any component fails, it will inevitably be accompanied by malfunctions. For car lighting failures, the entire lighting system must be carefully checked, each function used one by one, and the malfunction symptoms must be approved, and no omissions can be made. Fault phenomena provide a basis for fault analysis and are the basis of the entire process of troubleshooting. It is also a critical step. If the fault phenomena are not carefully investigated, resulting in information errors, it will affect the maintenance personnel's overall judgment and specific analysis ideas.
3.2 Analyze the cause of the failure
Based on the fault phenomenon, summarize and analyze it, infer which type of fault it belongs to, eliminate unreasonable possibilities, and screen out the scope of the fault. For example, it is found that the left rear brake light of the vehicle does not light up, but the other lights are normal. From this, it can be inferred that the lighting system as a whole is normal and the entire circuit is smooth. The cause of the fault can only be a problem with some parts, because if the main line of the lighting system is broken or If there is serious damage, other functions will inevitably be affected, so it is impossible that the brake light on one side does not light up. Therefore, the fault scope can be narrowed to the branch circuit of the rear brake light, and it is inferred that the cause of the fault is damage to the left rear brake light or an open circuit of the branch circuit.
3.3 Draw a tree diagram
The fault causes summarized by analysis will be listed in a tree diagram according to categories. Tree diagram displays analysis results graphically and organizes objects in a parent-child hierarchical structure. It is an expression of enumeration method and is often used to group and classify things, or to conduct extended analysis of problems. Using tree diagrams, people can intuitively see the analysis results, the relationships between each other, and the overall hierarchical structure of the goals, which can make thinking clearer, logic more rigorous, content more organized, and easy inspection to avoid omissions. After analyzing the fault phenomenon, the maintenance personnel classify the analysis results according to their nature and draw a tree diagram. This first forms the first layer of the tree diagram, and then subdivides downwards for each major category to form The second level of relationship extends downward to the third level until the specific cause of the failure can be accurately expressed. Through the tree diagram, the entire analysis process is clear at a glance, which facilitates maintenance personnel to conduct secondary sorting and reverse inspection. This not only avoids repeated analysis, but also prevents misunderstandings in thinking that lead to wrong conclusions. It also enables timely discovery of previously ignored content, maximizing The extent to which the analysis results are complete and accurate.
3.4 Eliminate from easy to difficult
Based on the analysis results of the tree diagram, start troubleshooting. The principle of troubleshooting is to start with the easiest and most common causes of failures. Compared with ten years ago, the manufacturing level of today's automobile industry has made great progress. At present, during normal use of automobiles, the possibility of sudden systemic failures is very small, and most of the failures occur in wearing parts. . Therefore, when troubleshooting, start with the most common and easiest to eliminate causes of failures, which can maximize maintenance efficiency and save time and cost.
4 Method Application
Use the above analysis method to solve the actual case: There is a 2013 Sagitar. The fault is that the left front headlight does not light up, but the other lights can be used normally. Try to eliminate this fault.
First, check the information and find the vehicle circuit diagram of the Sagitar 13 model. By searching the catalog, the lighting system circuit was identified in Chapter 57 - Basic Equipment. Read the circuit diagram carefully and analyze the control process of low beam lighting. By finding the low-beam light bulb, reverse search and sort out the logical relationship of the entire circuit and summarize it. When the car light switch E1 is rotated to the low beam position, E1 will communicate with J519 (vehicle power grid control unit), and J519 will control the coil of J680 (power supply relay) to energize, thereby closing the electric shock of J680, connecting the main circuit of J680, and J680's When it is turned on, it supplies power to the coil inside J331 (low beam relay). The electric shock of J331 is closed, and the main circuit of J331 is turned on, thus supplying power to the low beam bulb. It should be noted that J331 supplies power to the left and right low beam lights at the same time. After the current flows through J331, there are fuse SC18, left low beam bulb L29, wires and grounding points on the left low beam branch.
Then, we analyze the cause of the failure based on the control process of the low beam circuit. Since only the left front low beam of the vehicle does not light up, the light switch E1 cannot be the fault point, because if E1 fails, there will be no electrical signal transmitted to J519, and J519 will not control J680, so the result is low beam. The light relay cannot be turned on, and the left and right low beam lights do not light up at the same time. By analogy, J680 and J331 will not be fault points, and the lines from light switch E1 to J519, J519 to J680, and J680 to J331 cannot have open circuits, because once there is an open circuit in the above lines, the left and right circuits will be cut off at the same time. Power supply for both dipped beam headlights. At this point, we can conclude that the cause of the fault lies in the circuit part after J331, that is, the circuit from J331 to fuse SC18, the SC18 fuse itself, SC18 to the left low beam circuit, the left low beam bulb, the left low beam to Among the parts of the ground point circuit and the ground point of the left low-beam circuit, a closer look at the circuit diagram revealed that the low-beam ground circuit is shared with other lights, so the ground circuit fault can be eliminated, so there are only 4 types left. possibilities, as shown in Figure 1.
Figure 1 Failure cause analysis diagram
When troubleshooting the above four fault possibilities, use simple and quick operation methods. Prepare a car multimeter, adjust it to the voltage range, connect the black test lead of the multimeter to the car body, place the red test lead at the 18a port of fuse SC18, then turn on the light switch E1, rotate it to the low beam position, and check the multimeter reading. If the voltmeter has no value, it means that the line from J331 to the fuse is open, and the cause of the fault has been found. If the voltage value is large (within 12V), it means that the line before the fuse is normal. Continue to investigate one by one along the direction of the current. Next, if the black test lead does not move, move the red test lead to the 18b port of SC18. In the same way, check the multimeter reading. If there is no reading, the fuse itself is damaged. If the reading is large, it means that the fuse itself is not faulty. Continue to investigate. According to this method, next measure the bulb terminal T10l/6. If the terminal voltage value is normal, it can be determined that the bulb is faulty. The final test result was that the bulb itself was faulty. After replacing the bulb, the fault was eliminated. There are many ways to troubleshoot this problem, but using a multimeter to detect it is easy to operate and can quickly determine the fault point. In the actual maintenance process, we must fully consider the convenience of implementing the operation method, try to use simple and easy methods, and start with convenience to eliminate the cause of the fault that saves time and effort.
5 Conclusion
The lighting system is an important part of the vehicle. When dealing with its faults, maintenance personnel must have a complete set of diagnostic methods. The method discussed in this article starts from the preliminary data preparation and review, through the learning of basic circuit knowledge, analysis and induction of specific faults, then sorting out the overall ideas, drawing a tree diagram, and finally formulating and implementing an appropriate detection plan. Step by step to find out the cause of the fault and solve the problem. Each link has a detailed description, which provides ideas and methods for maintenance personnel to solve related problems. It has a high practical reference value and is of great help in improving maintenance skills.
