Why does the engine fault light reset after power failure?
2 Answers
The engine control unit determines the engine fault to be temporary. Low internal temperature during winter startup: During cold starts in winter, insufficient gasoline atomization in the cylinders may trigger the fault light. As the engine warms up and temperature rises, the fault naturally resolves and the light turns off. Presence of engine faults: The engine fault signal is issued by the engine control unit. After the vehicle is turned off and power is disconnected, the engine control unit reboots and performs self-diagnostics again. If no issues affecting normal operation are detected, the fault light will turn off. When faults are detected, a yellow or red warning light will illuminate.
Last time my car did the same thing, the check engine light went off after the battery was disconnected, but came back on as soon as I started it. This is because the vehicle's computer automatically resets when power is cut, clearing previous temporary error codes—just like rebooting a phone clears the cache. However, if the underlying hardware issue isn’t fixed, such as a faulty oxygen sensor or clogged fuel line, the computer will detect the problem again during self-check and immediately illuminate the warning light. This isn’t a new issue; modern cars all have this system. I think the owner shouldn’t take chances—disconnecting the battery is only a temporary fix, and the real cause lies in the engine or sensors. It’s crucial to visit a professional repair shop ASAP to read the fault codes and diagnose the issue, or it might lead to bigger trouble. Safety comes first; don’t ignore potential hazards just to save a little money.
