Hi all! Just last nite I filled up my 97 Bonneville SE with 128,000 miles on the clock. Anywho...I filled the tank until the shut-off on the pump clicked off...I didnt top off at all. Put the nozzle back on the pump...got my credit card receipt...put the gas cap on....3 clicks. I pulled away from the gas station ....and all of a sudden I hear several loud booms from the gas tank...I though she was gonna blow right there...either that or I ran over an old lady and she was beating her cane on my gas tank! I drove it home....no check engine light...didnt think of checking pressure at the gas cap. I hop in it today and on the way to work..the check engine lite comes on. I forget about till around 5. After work I drive to Autozone and buy a replacement gas cap. It doesnt have the groove for the strap :( . Oh well...I remove the strap from the filler neck and install the new cap. I check the check engine code: P0440:Evap system malfunction...there were two codes and they both were P0440...according to my Actron scanner. Any thoughts on this? Anyone else experience the Big Bang? I guess i'll have to wait until tommorrow....or even my next fill-up to see if it really was the gas cap. Dang...I havent seen that little engine light for over a year now

what most likely happened was you slightly overfilled your gastank (even though you didnt mean to), and after capping the tank the pressure of the vapors vented off the tank was much higher than normal and that exploited a leak in an old dry hose. there is a chance that if you just clear the code it will not reappear, replacing the cap is ok but it sounds like the cap is working fine. if it does become a reoccuring problem, then inspect the rubber hoses in the evap system near the charcoal cannister and near the tank if applicable. replace as needed.