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Car fault diagnosis

After a car is manufactured and during use, failures inevitably occur due to various reasons, which affects the car's power, economy, and performance. Changes in control stability, safety of use, etc. Some car failures are sudden, and some develop gradually. When a car breaks down, it is beneficial to the use and maintenance of the car to be able to use experience and scientific knowledge to accurately and quickly diagnose the cause of the failure, find out the damaged parts and parts, and eliminate the fault as quickly as possible.

A car, a modern means of transportation, has a certain lifespan no matter what, from the day it is manufactured and leaves the factory. No matter how it is used, it will break down sooner or later. Therefore, it is relative not to malfunction during use, but it is inevitable that various malfunctions will occur. Therefore, analyzing and diagnosing the cause of the fault is helpful to make judgments so that the car can run in good technical condition.

(1) Causes of automobile failures

The main causes of automobile failures are:

1. The existence of vulnerable parts

In car design, it is impossible to ensure that all parts on the car have the same lifespan. Some parts of the car itself are wearing parts, such as air filter cores, spark plugs, engine oil, etc., which have short service lives and need to be replaced regularly. If not in time, Failure occurs when the car is replaced or damaged prematurely.

2. Differences in quality of the parts themselves

Automobiles and auto parts are produced in large quantities and by different manufacturers, so quality differences are inevitable. Problems will arise when using original parts, and even more problems will arise when parts from cooperative factories and unqualified parts are installed on cars. Therefore, all car manufacturers are working hard to improve the quality of parts and eliminate quality defects in the parts themselves.

3. Differences in the quality of automobile consumables

Consumables in automobiles mainly include fuel and lubricants. Poor quality of these additives will seriously affect the performance and service life of the automobile. Making the car more likely to break down. The addition of these supplies is often difficult to ensure by the user. If you are not careful, low-quality gasoline and low-quality lubricants will be added, which is extremely harmful to the car and engine. Maybe the car will have problems before the user even cares.

4. The environmental impact of car use

Cars are used in the open air and have a greater environmental impact. The highway road surface is wide and flat, and the vehicle speed is high, which is prone to breakdowns and accidents; the road is uneven, and the vehicle vibrates and bumps seriously, making it easy to be damaged. High power consumption in mountainous areas and long waiting times in cities will cause great changes in the working conditions of the car. Sometimes, if it cannot adapt, it will easily break down or cause sudden damage.

5. The impact of driving skills and driving methods

Driving skills have a great impact on car failures, and improper use has an even greater impact. Improper management of car use, failure to perform turn-in and regular maintenance as required, rough starting and rough driving will cause early damage and failure of the car.

6. The impact of automobile fault diagnosis technology and maintenance technology

Cars must be maintained regularly during use, and faults must be accurately diagnosed before they can be repaired. Technology is required in automobile use, maintenance, fault diagnosis and repair operations. Especially in modern automobiles, there are many high-tech applications, which requires automobile use and maintenance staff to understand and master automobile technology and advanced new technologies. If you don't know how to repair, you can't repair it randomly, and if you don't know how to do it, you can't mess around with it, lest old problems are not eliminated and new ones appear again.

Therefore, car faults widely exist in the entire process of automobile manufacturing, use, maintenance and repair work. Great attention should be paid to every link, especially when using the car, pay attention to car faults. Faults must be discovered and eliminated in time to reduce accidents during use of the car.

(2) Common car faults

Common car faults can be judged by experience, senses and instruments on the abnormal performance and appearance symptoms of the car.

Common faults mainly include:

1. Abnormal car performance

Abnormal car performance means poor power and economy of the car, which is mainly manifested in the obviously low maximum driving speed of the car and poor acceleration performance of the car. ; The car consumes a lot of fuel and oil. The ride comfort of the car is poor, and the vibration and noise of the car are significantly increased. The car's control stability is poor, the car is easy to deviate, and the front of the car oscillates; braking deviates, the braking distance is long or there is no braking, etc.

2. Abnormal operating conditions of the car

Some abnormal phenomena suddenly occur during the use of the car, which should be prevented: the engine suddenly stalls while driving; the car does not brake when braking is required ; The car cannot start in winter; cannot start after the engine is turned off; the steering suddenly fails while driving; and even worse, the car has a tire blowout or the car spontaneously ignites and catches fire. The symptoms are more obvious and the causes are more complicated. The main reason is that there is a fault inside the car that is not noticed and develops into sudden damage.

3. Abnormal car noises

When a car malfunctions during use, it is often most easily manifested in the form of abnormal noises. Under normal circumstances both the driver and passengers can hear it. Experienced people can judge the car fault based on the location of the abnormal sound and the different frequencies and timbres of the sound. Generally, the fault is more serious when the sound is dull and accompanied by strong buffeting. You should stop the car, reduce the engine speed or turn off the engine to find out. Some sounds indicate that some parts are malfunctioning, which does not affect the use of the car and cannot be found out at the moment. You can drive the car back to the base or drive to the nearest car maintenance department and ask experienced personnel to find it.

4. Car odor

The most avoidable odor is when the car is driving. Human sense of smell is very sensitive and will smell any odor. If there is an odor, you must first determine whether it is a car odor or an odor in the surrounding environment. Car odors mainly include the burnt smell emitted by non-metallic friction materials on brakes and clutches; the special smell of battery electrolyte; and the burnt smell of car electrical systems and wires. At certain times, you can smell the burning smell of leaking engine oil and the abnormal smell of gasoline, so you must pay full attention to it.

5. Car overheating

Car overheating means that the temperature of various parts of the car exceeds the normal operating temperature range. Engine overheating is most obvious when the radiator is boiling; transmission overheating, rear axle housing overheating, brake overheating, etc. can all be manifested by hand testing or water testing. If the car is overheating, further inspection is required to find the root cause of the fault. If it is indeed a long-term problem, Caused by high load, it generally does not affect use. If it is an internal mechanism failure, it should be diagnosed and eliminated in time.

6. Abnormal exhaust smoke color

The engine exhaust smoke color is the appearance of the engine working. When the engine is burning normally, there will be a certain exhaust smoke color. When the engine is not working properly, the exhaust smoke color will change. If the engine burns oil and the exhaust is blue, it indicates that the engine needs maintenance; if the engine is not completely burned, the exhaust is black, and the fuel should be replaced or the ignition timing should be adjusted; if the engine exhaust is white, it means there is water in the fuel or cylinder, and it should be checked fuel or check the engine.

7. Automobile leakage

Automobile leakage manifests as fuel leakage, engine oil leakage, coolant leakage, brake fluid leakage, steering oil leakage, lubricating oil leakage Leakage and refrigerant leakage, etc., as well as battery fluid leakage from the electrical system and current leakage from the electrical system. Car leaks can easily cause car overheating and structural damage. For example, leakage of steering oil can easily cause steering failure of the car; leakage of brake fluid can easily cause brake failure, etc.

8. The appearance of the car is abnormal

When a car is parked on a flat site and the appearance is checked, sometimes it is found that the car is skewed longitudinally or laterally, which shows abnormal appearance. Pay attention to check the car tire pressure, frame and suspension damage, body damage and other abnormal phenomena. Abnormal appearance of the car may affect the use of the car. For example, the car's center of gravity shifts, serious vibrations, unstable steering, and car deviation, etc.

9. Abnormal car driving

Abnormal car driving manifests itself as the car's inability to accelerate, steer and brake according to the driver's wishes, and the car's operating mechanisms and actuators can be detected If there is a fault, in addition to checking and adjusting the accelerator pedal, brake pedal, clutch pedal, steering wheel and their transmission mechanism, the car should also be fully inspected.

Only after the fault is found and the repairs are normal can it be used.

(3) Automobile fault diagnosis

During the use of automobiles, various faults will inevitably occur. If a car breaks down while driving, the driver must check, diagnose and troubleshoot on the spot before the car can continue to drive. Some faults are relatively large or complex and difficult for the driver to solve by themselves, and require car mechanics and Automobile maintenance engineering technicians come to inspect, diagnose and troubleshoot. Car faults are ever-changing, strange, and of many types, but the methods and steps for fault diagnosis are certain. As long as the basic methods are correct, the thinking is clear, and the methods are appropriate, fault diagnosis is easy to make.

The methods of automobile fault diagnosis can basically be summarized into 12 types: inquiry method, observation method, hearing method, test method, touch method, smell method, replacement method, instrument method, measurement method, and segmentation method. Inspection method and partial disassembly method, etc.

To apply these methods, you must have theoretical guidance; fully understand the use and maintenance of the car, and fully understand the occurrence of faults. For relatively simple faults on the car, the cause and location can be found only by experience and senses; for difficult faults, they can only be found with instruments and the application of specialized fault diagnosis equipment. With instruments and equipment, it is also necessary to Be able to use it, and you should also combine maintenance experience during use, flexibly use these fault diagnosis methods, and make a comprehensive evaluation of the fault. If you continue to practice, summarize and accumulate experience in diagnosis, you will be able to apply it freely.

2. Automobile fault diagnosis methods

(1) Diagnose faults by looking and asking

Doctors need to "look, smell, ask and feel" to see a doctor, and the same is true for car fault diagnosis. Looking and asking is an effective way to quickly diagnose car faults.

When a car breaks down, it needs to be diagnosed. When the repairman sees the car for the first time, he should make a preliminary judgment about the car's form and age. It is very important to understand the form of the car from its appearance. The service life can be judged from the appearance or by turning over the cab to expose the engine. Experienced maintenance personnel can even judge the car failure at once.

When a car needs to be repaired, the maintenance personnel must ask the user and owner, including the car model, age, repair status, usage, location and phenomenon of failure, and what to do after the failure. This is a shortcut to understand the fault as deeply as possible.

By understanding the form, the basic structure and performance of the car can be reflected. If you understand the form and structure of the car and have rich maintenance experience, the diagnosis will be easier; if you don’t understand enough, you can check the books and information. Can master it.

Through in-depth questioning, you can basically understand the location where the fault occurred. For example, you can ask whether the fault occurs in the engine or the transmission; if it is the engine, you can further understand whether it is an electrical fault or a mechanical fault; if it is a mechanical fault, you can also learn whether it is the crank connecting rod mechanism or the valve train, etc., and then make further decisions. Diagnosis is much easier. Once the fault is identified, troubleshooting and repair are easy.

If the user wants to overhaul the car, he should also ask about the repair of the engine powertrain, the car chassis, the car cab and body, the car electrical and the car air conditioner, etc. Which parts and assemblies are the focus of maintenance, etc., in order to determine the maintenance plan.

(2) Use the empirical method to diagnose faults

As the name suggests, the empirical method to diagnose faults is to quickly and accurately diagnose car faults based on the basic qualities and rich experience of the driver and maintenance personnel. Get a diagnosis.

The so-called basic quality, whether it is a driver or a car maintenance personnel, must learn from books and improve in practice, so as to obtain basic car knowledge and maintenance experience, which is very important. Automotive technology is a comprehensive reflection of the development of the national economy. Automotive technology is developing faster and faster, and there are more and more new technologies. Therefore, it is impossible not to work hard to learn from books and practice. For example, for the single pump oil supply and speed regulation technology of the diesel engine in the car, as well as the new foreign diesel engine technology, it is necessary to learn from books and materials on the basis of the original knowledge, and then carry out practical maintenance work.

Only practice under the guidance of theory is correct practice, and experience can be summarized and accumulated in practice.

The so-called maintenance experience is also very important. With experience in car maintenance, the same fault and similar faults can be solved at once. Experience includes personal experience, experience that has been summarized and accumulated; there is also experience learned from books and other ways. Only by combining the two can we continue to accumulate experience and make judgments on car faults more smoothly. For example, if the diesel engine fails and the cab is turned over, the turning mechanism is stuck and the cab cannot be turned over. An experienced person only needs to push, pry and release, and the cab will turn over immediately; The speed of the diesel engine rises sharply and the noise becomes louder and louder. If you are inexperienced, you will not be able to stall the diesel engine no matter how you move. If you are experienced, you only need to gently turn the fuel switching valve on the fuel tank 45°, and the diesel engine will stall immediately, thus avoiding a vicious accident. . It is not difficult to see that this is the result of accumulated experience. Therefore, we must constantly sum up experience, turn experience into a powerful weapon for car maintenance, constantly arm ourselves with new knowledge and new experiences, and use experience to solve various and even very complex difficult problems on cars.

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