To eliminate the fault of the automobile circuit, it is necessary to understand the principle of circuit control and master the inspection skills. Now introduce some clever investigation experience:
Replace the suspected faulty parts with new or well-functioning parts, observe whether the fault phenomenon has changed and use this to judge the fault. This method can be used if the coolant temperature on the car is abnormal and the temperature sensor is suspected to be faulty. If the new sensor is replaced, the abnormal temperature indication disappears, indicating that the original sensor is damaged. Although this method has a simple advantage, it requires a certain amount of accessories.
That is, when some electrical components are working (sometimes instantaneously), the sound status is used for troubleshooting
Check the method. If the starter of the ignition switch is turned on, the starter does not work. At this moment, you can listen for the click and click sound of the electromagnetic switch of the engine at the moment of turning on. If the sound is normal, it indicates that the contact disk of the electromagnetic switch is poorly contacted or severely ablated; if the sound is weak, it indicates that the electromagnetic switch coil is defective; if there is no sound, check whether the starter relay can conduct the starting circuit. Listening inspection is also applicable to the inspection of various types of relays. Usually the sound of the relay is weak, the contact may be ablated, the relay is completely silent, the relay coil may be damaged. Relay inspection can also be combined with “short circuit inspection” to further diagnose the fault.
Test lamp inspection:
For more and more electronic devices in modern cars, the old inspection method of the scraping test should be abandoned and a test light inspection should be adopted. If the electronically controlled fan fails, you can connect one end of the test light to the power terminal and the other end to ground when the thermal switch is checked. The test light is on, indicating that the power supply is normal. The fault may be in the thermal switch or fan relay. If the light is off, you should check the fan control circuit, safety device, etc. Test lamp inspection is applicable to the power supply inspection of various electrical equipment and control circuits.
Short circuit check:
The inspection method to stop the work of a component one after another to observe whether the fault has changed. Such as
If the starter does not run, you can use a wire to short-circuit the “battery” terminal of the starter relay and the “starter” terminal. If the starter runs normally, it means the starter relay is damaged. In addition, this method can also be used to check if the horn does not sound.
Check section by section:
Some of the longer circuits of the car are faulty, and can be divided into several sections (combined with the “test light check” method) to find out the faulty section.
Touch the contact parts of electrical appliances or circuits by hand, and check the method of failure by feeling the temperature difference
law. If the starter is running weakly, you can touch the temperature of the battery connection part with your hand. If the temperature is high, it indicates poor contact. Also, if you touch the porcelain body of the spark plug with your hand (the engine is turned off for about 10 minutes), the spark plug with a lower temperature does not work well.
Hanging fire inspection:
When it is determined or suspected that a certain cylinder of the engine is working poorly, it can be tested by the hanging fire method.
Unplug the high-voltage wire at the spark plug end of the cylinder during the operation of the machine, pull it from the spark plug by a gap of 5 mm to 7 mm, and implement “hanging fire”. If the engine working condition is obviously improved, it indicates that the spark plug is working poorly (the cause may be caused by sparks, or it may be caused by blow-by oil, excessive gas mixture, etc.); if the engine operating condition does not improve, the spark plug should be replaced.
For the electronic components and various coils of modern automobiles, fault diagnosis mainly depends on instrument (usually referred to as multimeter) inspection. Although the instrument inspection has the advantages of high efficiency and accuracy, it requires the operator to be proficient in the use of the instrument and the technical standards of the component under test in order to make an accurate judgment on the technical performance of the component under test.