What Are the Reasons for the Engine Malfunction Light Staying On?
3 Answers
The engine malfunction light may stay on for the following 7 main reasons: Sensor failure: The sensors mentioned here include those for coolant temperature, crankshaft position, air flow, intake air temperature, oxygen, etc. When these sensors are damaged, have poor contact, or experience signal interruption, the vehicle's ECU cannot accurately obtain engine data, triggering the engine malfunction light. Fuel quality issues: Failure to add fuel and engine oil as required by the manufacturer may cause engine wear, leading to the malfunction light turning on. Poor combustion of the air-fuel mixture: Poor combustion can result in engine carbon buildup or knocking. When detected by the oxygen sensor and reported to the ECU, the malfunction light will illuminate as a warning. Issues such as spark plug failure, ignition coil failure, fuel pump failure, or fuel line blockage can all lead to poor combustion of the engine's air-fuel mixture. Turbocharging issues: The intake turbocharging pipeline and turbocharger can also cause the engine malfunction light to turn on. The most common issue is turbocharger damage, accompanied by symptoms such as oil leaks, excessive oil consumption, reduced power, metallic noises, or blue/black smoke from the exhaust pipe. Intake issues: Problems with the vehicle's intake can lead to engine pipeline blockages, and in severe cases, trigger the engine malfunction light. A dirty air filter that is not cleaned regularly can cause intake problems. Exhaust issues: Exhaust system failures can also cause the engine malfunction light to illuminate. Causes of exhaust problems include failures of the rear oxygen sensor, catalytic converter, exhaust camshaft, and bearings, with the catalytic converter being the most common. Using leaded gasoline, lead or silicon-containing lubricant additives, physical damage to the catalytic converter, or faults in the engine fuel supply system can easily lead to catalytic converter failure. Anti-theft system failure: If the vehicle's electronic anti-theft system malfunctions or if the anti-theft controller does not match the engine electronic controller, the anti-theft system can prevent the engine from operating normally, accompanied by the engine malfunction light turning on. If the engine malfunction light is on, follow these steps: First, check if the engine is running normally, looking for symptoms such as shaking or black smoke. If present, avoid restarting the engine. Note: Do not restart the engine if the red warning light is on. If the engine can be started, turn it off and wait for 5-10 minutes. Without pressing the brake, press the start button once or turn the key halfway to the 'on' position without depressing the clutch. The vehicle will perform a self-check upon powering on. After 5-10 seconds, observe whether the malfunction light on the dashboard turns off. If the malfunction light remains on, visit a service station as soon as possible to diagnose the issue. The service station can use a portable diagnostic tool to read the fault codes, obtain fault information, and perform targeted repairs.
I remember encountering the check engine light staying on while driving before, and it took me a long time to figure it out. It was quite annoying—it could be an issue with the oxygen sensor, which monitors exhaust emissions. Once it gets dirty or fails, the ECU will trigger the warning light. It might also be due to a clogged catalytic converter, affecting emission purification. Another possible cause is an abnormal air-fuel ratio, such as a dirty mass airflow sensor leading to inaccurate air intake measurements. Sometimes, worn spark plugs or faulty ignition coils can also trigger the light. My fuel consumption suddenly spiked, and after inspection, these issues were identified. I recommend using an OBD scanner to read the trouble codes as soon as possible—don’t delay too long, as it could not only increase fuel consumption but also harm engine performance. Pay attention to these small details during routine maintenance; prevention is better than repair.
A friend of mine just bought a used car, and within a few days, the engine warning light came on and stayed lit, which really worried him. At the repair shop, they found out it was a faulty oxygen sensor that needed replacement. Additionally, the ECU stored error codes pointing to ignition system issues, such as worn-out spark plugs or coils. The mechanic warned that ignoring the problem could lead to anything from exhaust emission fines to engine misfires or even stalling. He also mentioned that fuel system issues, like clogged fuel injectors, could trigger the warning light. After that repair, my friend learned his lesson and now regularly cleans the air filter and checks the sensors. Driving safety comes first—when the warning light is on, it's best not to push your luck and instead visit a professional shop to prevent minor issues from turning into major headaches. Regular maintenance is crucial, especially for used cars, which require extra attention.
