the other day i got a message on my dashboard that said check gas cap or something like that. i checked it and didnt notice anything.

a couple weeks later, when i went to fill up on gas, i thought something looked different. isn't there supposed to be a metal flap that opens when you stick the gas nozzle in the tank? if it is, then mine must have broke off and went into the tank. i have a 2006 civic. if it is in the tank, i didn't know if it could cause a problem.

 

i fairly certain there is a mesh screen between the filler and tank to prevent theft and dibris from entering the tank.

 

Check the rubber seal on the gas cap. If it is cracked, that will make the light come on and you should replace the cap.

The little door is part of a very old federal requirement to try and make it difficult to put leaded gas into a newer car that requires unleaded. It's kind of pointless now since no stations sell leaded gas. If something like that door falls down into the tank, it will just lay on the bottom and not cause any problems. Having it break off probably means that someone tried to put a siphon hose in there to steal your gas.