Why Does the Engine Malfunction Light Stay On After Refueling?
3 Answers
After refueling, if the engine malfunction light stays on, it indicates the use of substandard fuel. During the combustion process in the engine, substandard fuel with high impurities and low combustion efficiency can leave residues and unburned fuel in the combustion chamber, occupying space and triggering the engine malfunction light. Solution: Promptly drain the substandard fuel and clean the fuel tank and fuel lines. After cleaning, replace with high-quality fuel. Besides fuel quality, other reasons that can cause the engine malfunction light to stay on include: Sensor Malfunction: Sensors such as coolant temperature, crankshaft position, air flow, intake air temperature, and oxygen sensors, when damaged, poorly connected, or interrupted, prevent the car's ECU from accurately obtaining engine data, leading to the engine malfunction light. Poor Mixture Combustion: Poor combustion of the air-fuel mixture can cause engine carbon buildup or knocking. Monitored by the oxygen sensor and reported to the ECU, this triggers the malfunction light. Issues like faulty spark plugs, ignition coils, fuel pump, or clogged fuel lines can lead to poor mixture combustion. Turbocharger Issues: Problems with the intake boost pipes or turbocharger can also trigger the engine malfunction light. The most common issue is turbocharger damage, accompanied by symptoms like oil leaks, excessive oil consumption, reduced power, metallic noises, or blue/black smoke from the exhaust. Intake Problems: If the car's intake system is compromised, it can lead to clogged engine pipes, and in severe cases, trigger the engine malfunction light. A dirty air filter that isn't cleaned regularly can cause intake issues. Exhaust Problems: Exhaust system faults can also activate the engine malfunction light. Common causes include faulty rear oxygen sensors, catalytic converters, exhaust camshafts, or bearings, with the catalytic converter being the most frequent issue. Using leaded gasoline, lead or silicon-based lubricant additives, physical damage to the catalytic converter, or fuel system malfunctions can easily cause catalytic converter failure. Anti-Theft System Fault: If the car's electronic anti-theft system malfunctions or the anti-theft controller doesn't match the engine's electronic controller, the anti-theft system can prevent the engine from operating normally, also triggering the engine malfunction light.
I encountered the same issue last time after refueling, which was really frustrating. When the engine malfunction light came on, I immediately drove to the repair shop for a check. The mechanic said the reasons could be various: the most common one is the fuel cap not being tightened properly, causing fuel vapor leakage, and the system will light up the warning when detecting an anomaly; it could also be due to poor-quality gasoline, where impurities affect the oxygen sensor's operation; for older cars, it might be caused by overfilling the tank, flooding the charcoal canister, and the activated charcoal inside getting damp and failing, which can also trigger a fault code. It's recommended that you immediately check if the fuel cap clicks three times to ensure it's sealed properly, or try a different reputable gas station and observe for a few days. If the light still doesn't go off, you must use a diagnostic tool to read the fault code. In my case, it was a faulty charcoal canister purge valve, and replacing it solved the problem.
I've looked into the issue of the check engine light coming on right after refueling. There are three common scenarios: physical issues like a loose fuel cap or water-contaminated gasoline; sensor problems such as contaminated fuel pressure sensors or faulty EVAP system pressure detection; and long-term risks like carbon buildup clogging injectors from using low-octane fuel for extended periods. Especially in summer, overfilling the tank can cause gasoline to expand with heat and overflow into the EVAP lines, triggering errors. The solution is simple: turn off the engine, open and securely reseal the fuel cap to reset the seal; replace half a tank with high-octane fuel to flush the system; then drive about 20km to let the vehicle run self-diagnostics. In most cases, the light will turn off by itself - last time I tried this method, it cleared within two hours.
