What is the reason for the yellow engine fault light being on when the engine is not started?
3 Answers
When the engine fault light is on without the engine being started, it is a normal self-check of the vehicle, indicating that the engine is not yet operational. Before the car is ignited, the vehicle enters a self-check state, and the engine fault light will illuminate. It will turn off after the car starts normally. If the engine fault light remains on after the car is started, it indicates a problem with the engine's working condition. The following are common engine faults: Starter damage: Includes insufficient battery power, damaged circuit fuses, or broken starter wires, leading to engine ignition failure. Unstable RPM during operation: The engine's RPM fluctuates significantly during operation, often due to gas leaks in the intake system. Slow RPM change during rapid acceleration: When the car accelerates rapidly, the engine RPM changes slowly, which can be caused by low ignition voltage or delayed ignition timing. Solutions: Adjust, repair, or replace the throttle position sensor. Clean or replace the fuel injector and replace the spark plugs. The yellow fault indicator light indicates an engine fault, and the engine fault signal is sent by the ECU (Engine Control Unit), which controls all electronic devices of the engine.
I've encountered this situation before, and a friend who just bought a car also asked about it. Let me recall. When the vehicle isn't started and you only turn the key to the ON position, the yellow light coming on is usually part of the normal self-check operation. The electronic system is inspecting engine components like sensors and emission controls, and the light indicates it's in diagnostic mode. After starting the engine, it should turn off. If it doesn't, then there might be an issue. Common causes include: the battery voltage being too low, leading to a system error detection; uncleared fault codes, such as a failed oxygen sensor; or unresolved issues from the last maintenance. I suggest not to panic—try starting the engine first to see if the light changes. If it stays on, it's best to use an OBD scanner to check the codes or visit a repair shop to avoid affecting driving safety. Anyway, keeping a simple diagnostic tool in the car can save a lot of hassle.
I've been driving for years and have encountered similar warnings, so let me share some insights. When the fault light flashes yellow before starting, it's by design in most cars—the computer is performing a preheating check, covering the fuel system, etc. If the light goes off after starting, everything's fine; if it stays on, it might indicate an aging battery with insufficient power supply or a faulty throttle sensor needing cleaning. I make it a habit to regularly check the dashboard status, especially in cold weather when the battery is weaker and false alarms are more common. Last time my car had this issue, replacing the battery fixed it. For safety, don't ignore this small signal; I recommend checking if the wire connections are loose or corroded.
