All vehicles (gasoline) for many years have had
a charcoal canister, it is to clean the vapors
that could come from the fuel tank, and
every so often the engine will draw these
vapors into the intake manifold where they
get burned with the intake charge.
It's just another smog fighting device, along
with your non-venting gas cap, which forces
these vapors into the charcoal canister so they
don't get into the air without being burned
Wild