Why does the engine yellow light come on after filling up a full tank of gas?

[LilyRose]

If the engine warning light comes on immediately after refueling, it is usually due to poor fuel quality. In such cases, the engine warning light typically turns off by itself about 30 seconds after restarting the car following refueling. The emission system is highly sensitive to fuel quality, so it is advisable to refuel at reputable gas stations and avoid low-quality fuel unless absolutely necessary. If low-quality fuel has been added, immediately take the car to a service station to clean the fuel tank and fuel lines. Here are some engine maintenance tips: 1. Use lubricating oil of the appropriate quality grade: For gasoline engines, select SD–SF grade oil based on the additional equipment in the intake and exhaust systems and usage conditions; for diesel engines, choose CB–CD grade oil according to mechanical load, ensuring the standard meets or exceeds the manufacturer's requirements. 2. Regularly change the oil and filter: The quality of any lubricating oil deteriorates over time. After a certain mileage, degraded oil can cause various engine problems. To prevent issues, change the oil regularly based on usage conditions and maintain an appropriate oil level (usually up to the upper mark on the dipstick). As oil passes through the filter, solid particles and sludge accumulate in it. If the filter becomes clogged, oil may bypass the filter through the safety valve, carrying contaminants back to the lubrication system, accelerating engine wear and increasing internal contamination. 3. Ensure proper crankcase ventilation: Most gasoline engines are equipped with a PCV (Positive Crankcase Ventilation) valve to promote ventilation, but contaminants from blow-by gases can accumulate around the valve, potentially clogging it. A clogged PCV valve can cause polluted gases to flow back into the air filter, contaminating the filter element and reducing filtration efficiency. This leads to dirtier air-fuel mixtures, further polluting the crankcase, increasing fuel consumption, accelerating engine wear, and even causing engine damage. Therefore, regularly maintain the PCV valve and clean surrounding contaminants. 4. Periodically clean the crankcase: During engine operation, high-pressure unburned gases, acids, moisture, sulfur, and nitrogen oxides from the combustion chamber enter the crankcase through the gap between the piston rings and cylinder walls, mixing with metal particles from wear to form sludge. Small amounts remain suspended in the oil, while larger amounts precipitate, clogging filters and oil passages, making lubrication difficult and causing wear. Additionally, oil oxidizes at high temperatures, forming varnish and carbon deposits on pistons, increasing fuel consumption, reducing power, and in severe cases, causing piston rings to seize and leading to cylinder scoring. 5. Regularly clean the fuel system: As fuel flows through the system to the combustion chamber, it inevitably forms gums and carbon deposits, which accumulate in fuel lines, carburetors, injectors, and combustion chambers, disrupting fuel flow, altering the air-fuel ratio, and impairing fuel atomization. This can cause engine issues such as rough idling, knocking, hesitation, and poor acceleration.

[Jeremiah]

I've encountered this issue several times, likely related to the fuel tank cap. If the cap isn't tightened properly after refueling, it can cause vapor leakage, triggering the engine computer to illuminate the warning light. It could also be fuel quality issues - some small gas stations sell fuel with more impurities that may cause incomplete combustion. Additionally, overfilling the tank can submerge the charcoal canister, causing problems with the fuel vapor recovery system. Another possibility is a stuck float sensor in the fuel tank giving false fault readings. My suggestion is to first tighten the fuel cap and drive about 50 kilometers - usually the light will turn off automatically. If it remains on, you'll need to visit a dealership to scan for specific trouble codes.