The "Ask a Mechanic" Thread in The Tailgate Posted January 22, 2010 I have a question. I took my car to a quicky lube the other day and now my check engine light is on. WTH? Did they put any oil back in it? (inside joke)I see a real mechanic in your future,but ya might try taking it back first. Have you filled up gas since then?...make sure the gas cap is tight. That's exactly what I'd do. Some places will add fuel injector cleaner to your gas tank after an oil change, but if the gas cap isn't securely on a sensor could detect it and manifest with a check engine light. Its happened to me a few times.