It will keep the codes stored for a while even though the CEL is now off. It just means the conditions for causing the CEL to light up are not occurring now. It's entirely possible the codes are due to marginal voltage due to a weak battery, but you should have had starting issues as well (slow cranking, etc). My Ram had the went into limp mode with the CEL coming on (codes indicated seleonoid pack needs replacement - confirmed by dealer). What I have noticed is the CEL will eventually stay off after a few days whether I drive it or not. But I'm sure the codes are still stored.