fuel tank has air inside and does not fillup
It's not an airlock' in the strictest definition, it's part of EVAP emissions system. When you fill up, the gas going in displaces air and gas fumes and those fumes (are supposed to) go in to a vent from the tank to a charcoal filled canister the soaks up the fumes, instead of coming out in your face and in to the air we all breathe. The fumes in the canister are purged by intake vacuum when engine is started. You have either a blocked vent tube, a bad valve or the fumes are not being purged and have collected so much there is liquid gasoline in the canister, backing up and not allowing the air/fumes in. You need to have it looked at by a mechanic. This is a diagram of how it works, generic, not your car exactly but same basics.. Click image to size up
Another example. That is why one of, if not the most common causes for a CEL (Check Engine) light to come on is a missing or non-sealed gas cap. The ECU can detect that as a leak
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