Most customers that come into the shop to get a problem diagnosed don’t know what the actual problem is, just the symptoms. Sometimes people come in and tell us what they think the problem is, but they might not be correct. This was one time a car came in and the information they gave us was correct.
The 2016 and newer Honda Civics have the new capless fuel fillers. The car that came in had the check engine light on, and either the customer or another shop had read the code and found that it was an evaporative emissions control system leak. They also had found a small round seal sitting behind the fuel door, next to the capless filler port.
There is an outer flap and then an inner flap that actually seals the filler neck. Somehow, the seal on that inner flap had come off, and then come out of the assembly altogether. I’m not sure how that happened, but if it hadn’t, I would’ve had to spend a lot more time trying to find where the system was leaking.
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