What is the reason for the engine fault light being on after power-on but off after ignition?
2 Answers
After power-on, the engine fault light is on, and the reason it turns off after ignition depends on the engine's operating condition. Below are the specific reasons for the fault light being on in different scenarios but turning off after ignition: 1. Engine not started: The engine is not running, so the oil pump and alternator are not working. At this time, the alternator is not generating electricity, and there is no oil pressure, so these two indicator lights are to inform the driver of the vehicle's operating status. 2. After engine start: Once the engine starts, the alternator and oil pump begin to work. At this point, the alternator starts generating electricity, and the oil pump operates to ensure the oil reaches a certain pressure to meet the engine's operational needs, so these two warning lights will turn off, indicating the system is functioning normally. However, if the engine is running and the warning lights remain on, it indicates a fault in the vehicle's charging system or an issue with oil pressure. The engine should be turned off, and the vehicle should be inspected (primarily the oil system, as continued operation with an oil pressure warning may cause severe engine damage).
After powering on, the engine warning light illuminating could be part of the vehicle's normal self-check process. If the light turns off after starting the engine, it indicates the system hasn't detected major issues. With over a decade of driving experience, I've frequently encountered this phenomenon—no need for excessive concern. The ECU scans sensors and circuits during power-up, and the warning light simply indicates it's reporting pending checks. If the engine runs normally after startup, the light will naturally extinguish. However, if the light remains steadily lit or flashes during power-up, remain vigilant—there might be stored trouble codes, such as a dirty oxygen sensor or insufficient oil pressure. Regular maintenance like periodic air filter and oil changes helps prevent minor issues from accumulating. Always prioritize driving safety; if you notice abnormal noises or vibrations, promptly consult a professional mechanic.
