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Q: Gas tank door burnt black.

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The other evening as I was driving, my check engine light came on. I stopped to check it out and nothing appeared to be wrong. My car runs just as normal as it always has. The next morning, I took it by Advanced Auto and they did a test on it. The code P0440 popped up. I was told it was a small leak in my EVAP emissions system. I stopped by a mechanic to get it checked out further but they were swamped. When I told them the code they did tell me that it was not a huge issue to worry about and that I could drive the car with no issues. I will be going next month to get it looked at and fixed but right now I don't have the money to do so. Well, this afternoon (it has been about 4 to 5 days since check engine light came on) ... I was outside and I noticed my gas door looked black on the inner outer edge. I open it and the entire inner door is black. This is not the black stuff that you can easily wipe off. This appears to be burnt onto the door flap. It is also on the insde walls.

My car has 146734 miles.
My car has an automatic transmission.

A: The most common cause for a P0440 code is t...

The most common cause for a P0440 code is the fuel cap seal. I suggest making sure that the fuel cap is tight by turning until it clicks. If you are sure that your fuel cap was tight, replace the fuel cap and reset the codes. If it returns, you may need to have the evaporative system smoke tested to see where the leaks are.

I don’t really have a good answer for the fuel door being black except if you smoke, its possible that vapor buildup from a faulty gas cap seal ignited under the flap from a still burning cigarette or some other ignition source.

I’d suggest getting you car looked at by a certified technician, like one from YourMechanic, who can diagnose your Check Engine Light further and suggest a fix from there. Best of luck.

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