How are fuel tanks vented? How do gas caps go bad?

[J]

On an 8th generation Honda Civic does anyone happen to know how fuel tanks are vented?

I think in order for the fuel pump to suck fuel in without caving the fuel tank in, air must find its way into the tank somehow right? Does anyone know how?
When the fuel expands due to heat, air must be pushed out of the tank right? Does anyone know how?

Also on a Honda Civic the gas cap does not appear to be made of solid plastic, it has metal components and stuff in it. Does anyone know what this stuff does? Can it go bad?

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[zero]

Not specifically, but since sometime around the eighties cars (and trucks) have have evaporative emissions systems. Or EVAP for short. On modern cars these consist of a series of valves, pressure sensors and a charcoal canister to hold fuel vapour to keep the pressure in the tank within a certain range.

The rubber seal on a gas cap goes bad and the system can’t regulate the pressure, so a code is set. The other components are what allows the cap to “click” when you tighten it.

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