There are many diagnostic methods for car circuit and electrical failures. The following car repairs will give you a summary. As for when to use which diagnostic method, you will know some more after reading it, and those who don’t understand will consider it carefully.
1. Intuitive diagnosis method Intuitive diagnosis method is the first/step of repairing automobile electrical appliances, and it is also a simple step. It only depends on the direct feeling and experience of the inspector to check and eliminate the fault. When a certain part of the car's electrical system fails, there will be abnormal phenomena such as smoke, sparks, abnormal noise, burnt smell, and high temperature. Through the sensory organs of the human body, the appearance of automobile electrical appliances can be inspected by the methods of looking, smelling, asking, cutting, and smelling to determine the location of the fault. For maintenance personnel with certain experience, some more complicated faults can be found, which greatly improves the speed of maintenance. For example, when a car is driving, when the turn signal switch is turned on, it is suddenly found that the turn signal light and the turn indicator light are not on. Touching it with your hand, it feels that the flash relay is hot, indicating that the flash relay has been burned out. When electrical components are working normally, they should have a suitable working temperature. If the temperature is too high or too low, it will mean a fault. For example: when the starter is running weakly, if the battery poles are in poor contact with the wires, they will feel hot when touched.
2. Diagnosis method of grounding fire test It is a method to judge the fault according to the intensity of the spark generated by removing a wire end of the electrical equipment to test the metal part of the car. This method is relatively simple, and is a simple and convenient method often used by the majority of automotive electronics and electrical maintenance workers. Systems that use electronic equipment are generally not allowed to use this method, and must be carried out in accordance with certain methods with the help of some instruments and tools. Otherwise, the overcurrent generated by the "fire test" will bring unexpected damage to certain circuits and components.
The research and development of the automobile bus system can be divided into three stages: the first stage is to study the basic control system of the automobile (also known as the comfort bus system), such as lighting, power windows, and centralized control locks. The second stage is to study the main control system of the automobile (also called the power bus system), such as electronic injection ECU control system, ABS system, automatic transmission, etc. The third stage is to study the integration, real-time control and information feedback between the various electronic control systems of the automobile. According to my country's automotive electronic technology development plan, after entering the 21st century, car electronic technology can reach the level of foreign cars in the 1990s. In order to shorten the gap with foreign car technology and improve its own competitiveness, simply relying on technology introduction is not conducive to development. Research and development of one's own car bus and network application system are on the rise. At present, the research and application of automobile bus in my country is still in its infancy, and the application trend of automobile bus is obvious. Now it is a good time to intervene in this research. The focus of research on automobile bus. As my country’s models are mainly European and American models, and European and American models are mainly CAN bus, the current domestic models using bus technology almost all use CAN bus. Therefore, the research and development of automobile bus should be selected based on the actual situation at home and abroad. CAN bus. CAN conforms to the ISO/OSI reference model, but only specifies the protocol of the physical layer and the data link layer, and the protocol of the application layer needs to be defined by the user. There are many chips that support CAN low-level protocols, including on-chip MCUs and off-chip CAN controllers. There are also many application layer protocols developed by users. For example, the DEVICENET protocol defined by AB is an application layer protocol based on the CAN protocol. The SDS bus launched by Honeywell also defines its own application layer on the basis of CAN. It can be seen that the focus of the research on the automotive CAN bus is to develop ECU hardware and application layer software for specific models, and form an in-vehicle network. Key technology Use CAN bus to build an in-vehicle network. The key technical issues that need to be resolved are: 1) Technical issues such as the rate, capacity, priority, and node capacity of information transmitted by the bus; 2) Reliable data transmission in a high electromagnetic interference environment; 3) Determine the maximum transmission delay time; 4) Network fault-tolerant technology; 5) Network monitoring and fault diagnosis functions; Overview of the bus network system As the performance of the automotive electronic control system improves, especially the controller chip and software performance With the improvement of the automobile bus network system, not only can share information and save wiring harnesses, but also provide richer software functions to enhance the value and competitiveness of products and meet the needs of automobile reliability and comfort. The bus technologies corresponding to these functions include: Network management: The controller monitors the network operation status through the network management, and once a communication failure is found, it immediately takes failure processing. The sleep and wake-up functions of network management can coordinate the power management of each controller, thereby reducing the battery power consumption when the vehicle is parked. Diagnosis: Diagnosis can not only read the fault code, but also realize the two important functions of offline configuration and detection, and program download. Automated offline configuration and detection functions can quickly and comprehensively configure and detect the functions of the controller (such as window zero configuration and anti-pinch detection), so as to ensure the quality of the car and speed up the production line. Through the program download function, the automaker can refresh the controller's software in the 4S shop, thereby reducing the cost of recalls caused by software defects. Measurement and calibration: In the development process of new models, the rapid control prototype controller using measurement and calibration technology can adjust the control parameters and algorithms in real time and conveniently through the computer and network system, which greatly reduces the development cycle and cost. This technology is widely used in the development of new energy vehicles in Europe, the United States and Japan. Foreign GM, Ford, Volkswagen, etc., as well as domestic FAW, Dongfeng, SAIC, Changan, GAC, Chery and other automakers have integrated bus technology into a generalized network platform for high, medium and low models.
One, understand the general sequence of automotive circuit diagrams
1 . The power supply is limited to the wires of the electric fuse or switch is the common front of the electric equipment. It is generally drawn on the upper part of the circuit diagram in the circuit schematic diagram.
2 . The circuit diagram of the standard drawing method, the contact of the switch is in the zero position or dynamic. That is, the switch is in the off state or the relay coil is in the non-energized state. The on and off of the elements with switching characteristics such as transistors and thyristors depends on the full house situation.
3. The characteristics of the automobile circuit are dual power supply, single wire system, each electrical appliance is connected in parallel with each other, and relays and switches are connected in series in the circuit.
4. Most of the power-consuming equipment passes through the fuse and is cherished by the fuse.
5. The whole vehicle circuit is composed of several independent circuits according to the effectiveness and working principle. This can solve the problem of the huge and chaotic circuit of the whole vehicle and the difficult analysis of the title. Nowadays, the entire automobile circuit is generally drawn according to the various circuit layouts, such as the power supply system, the starting system, the ignition system, the lighting system, the signal system, etc. These unit circuits have their own characteristics. The principle is thoroughly understood, and it is easy to understand the circuit of the whole car.
2. Responsible for reading circle notes
Responsible for reading the legend, understanding the title and technical type of the circuit diagram, and want to know how long it will take to learn car maintenance. Understand the meaning of graphic symbols and the correlation between equipment components and graphic symbols one by one, so that you can quickly and accurately recognize pictures.
Three, driving the circuit
In electricity, the circuit is the most basic, most important, and simplest concept. Any complete circuit is composed of power supply, electrical appliances, switches, wires, etc. Regarding the DC circuit, the current always goes from the positive pole of the power supply, and reaches the consumer through wires, fuses, and switches. Then go through the wire (or ground) and return to the negative pole of the same power source. In this process, only one link needs to be faulty, and this circuit will not be accurate and useful. For example: How long does it take to learn how to repair a car from the positive pole of the power supply? After a certain electrical appliance (or another electrical appliance), it finally returns to the positive pole of the same power source. Since the potential difference (voltage) of the power source is only between the positive and negative poles of the power source, the same electrode of the power source is equipotential. There is no voltage. This kind of "from positive to positive" approach does not produce current. In the car circuit. Generators and batteries are both power sources. When looking for a circuit, they should not be confused and cannot be driven from the positive pole of a power source. After going through a number of electrical equipment, return to the negative pole of another power supply, this way. No real path will be formed, and no current will appear. Take a look at car circuit repair training. So it must be exaggerated. The loop refers to driving from the positive pole of a power source, passing through the electrical appliances, and returning to the negative pole of the same power source.
Technical standards for gas pressure:
CA6102: 934KPaEQ6100 is not less than 834KPa, the use limit is 670KPa The fourth cylinder does not meet the conditions, you should check and calculate the average of the two measurements of each cylinder: then calculate the average pressure of the six cylinders.
Calculate whether the pressure difference of each cylinder exceeds 6% of the average
The maximum value of the average value is: 802.5x(1+5%)=842.625Kp8 The minimum value of the average value is: 8025x(1-5%)=762.375Kpa
If the measured average value is between (762.375-842625) Kpa, it meets the requirements. The fourth cylinder is less than the average value and should be checked.
Measuring cylinder pressure is a simple and scientific method of diagnosing engine failures. The correct use of the method of measuring cylinder pressure can accurately and quickly diagnose some common engine failures, especially those drivers and repairers should master.
The car should start smoothly when the ambient temperature is not lower than -5℃, and it is allowed to start no more than 3 times, and each start should not be more than 5s. Check that more than three starts or more than 5s are unqualified. Hot car starts on the engine. Under normal operating temperature, it can be started within 5 seconds. If it does not meet the requirements, the vacuum degree is unqualified. When the gasoline engine is idling, the vacuum degree of the intake manifold should be within the range of 57-70kPa. (The plane shall prevail) Failure to meet the requirements is the unqualified vacuum fluctuation range. When the engine is on, the intake manifold vacuum fluctuates
The six-cylinder gasoline engine does not exceed 3kPa, and the Sijiang gasoline engine does not exceed 5kPa. Use a tachometer and vacuum gauge to check the atmospheric pressure based on sea level.
Standard) Failure to meet the requirements is the unqualified cylinder pressure value. Cylinder compression pressure should meet the original design regulations. Use a tachometer. Cylinder pressure gauge inspection does not meet the requirements. The pressure difference of each cylinder is the difference between the pressure of each cylinder and the average pressure of each cylinder. Not exceed 89, diesel engine not more than 10% using tachometer, cylinder pressure gauge or engine comprehensive analyzer to measure failure to meet the requirements as unqualified
Engine power evaluation indicators include: engine effective power (shaft power, rated power, standard power) and engine effective torque, calibrated speed, etc. are all evaluation indicators of engine power.
Limit planting: The power of the vehicle in use cannot be lower than 75% of the rated power, and it cannot be lower than 90% after overhaul.