i had just filled my 97 pontiac gp up with fuel ( 92 octane ) , when leaving the gas station the light came on i did fill it way over the full marker. like i always try to do. but i just tuned it up ( spark plugs,wires, pvc valve, oil, air filter). but now the check engine light is on. first time i filled after tune up seems odd sounds like it running same just cant figure out why its on. gonna go get codes tommorow but need some insight. thanks guys. i also added tranny fluid, maybe i overfilled?