(04 Cavalier) I'm getting P0455. New gas cap didn't help, & I didn't
see anything flagrant on visual inspection.

Reading about the EVAP codes, it seems that P0455 means a "large leak",
while P0440 means the self-test can't reach its target tank vacuum ...
which I'd think would also imply a 'large leak'.

Is there some useful difference between these codes?

Thanks