EVAP Canister
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
The canister is filled with carbon pellets used to absorb and store fuel vapors. See Fig 1 . Fuel vapor is stored in the canister until the PCM determines that the vapor can be consumed in the normal combustion process.