The activated charcoal canister is connected to the fuel tank by a group of tank vent hoses…The canister itself is usually located tucked away under the hood…By over-filling your gas tank, you can force liquid gasoline into this vapor collecting device…This canister was not designed to hold liquid gasoline. It can not purge this liquid properly which results in the CEL illuminating caused by any number of EVAP Sys trouble codes which can be difficult to properly diagnose and repair and the parts involved can be difficult to find and when found, tend to be expensive…
Which leads to this question… Why would anybody want to force-feed every last drop possible into their fuel tank??