A systematic approach is required for diagnosing automotive circuit faults. For example, oxidation of battery terminals can cause abnormal power supply. The alternator output voltage should be stable between 13.8-14.5V; if it is lower than 12.4V, the battery or charging system needs to be checked. For concealed faults, the test light method can quickly verify circuit continuity, while the short-circuit method and open-circuit method can locate open-circuit or short-circuit issues respectively. Care should be taken to avoid direct short-circuiting of the power supply during operation. For modern vehicles, It is best to first connect an OBD scanner to retrieve trouble codes; for instance, P-codes can precisely indicate abnormalities in sensors or control modules. If an ignition system fault is suspected, an oscilloscope can be used to analyze whether the crankshaft position sensor waveform is distorted, or the spark plug performance can be tested using the spark test method. Complex faults require voltage drop analysis in conjunction with wiring diagrams; for example, poor contact in the ECU power supply circuit may cause electrical malfunctions throughout the vehicle. During repairs, follow the principle of static testing first followed by dynamic verification, starting with vulnerable components such as fuses and relays and troubleshooting systematically. If necessary, replace suspected faulty components for verification. Professional tools like diagnostic scanners and oscilloscopes can significantly improve efficiency, but basic tools such as multimeters and test lights are also suitable for diagnosing most common faults.
