Question for anyone out there. I just bought a 2000 2.7T A6 and the CEL turns on every time I fill up the gas tank. I do make sure the gas cap is tight and clicks. The CEL turns on after driving for about 1 day with the full tank.

Once the car's gas goes below 1/2 tank of gas, the CEL automatically turns off.

I have filled up the car with 93 octane for the past month and there has been no other changes to the car. This is a consistent issue that never fails after the fill up.

any replies would be great!

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2000 A6 2.7T

We have this same car and had the same problem. It is an O2 sensor I believe that is what they called it. This is a recall item and we had it replaced at an Audi dealership at no charge. Good luck.