Is my check engine light being on something very serious? on 2001 Chrysler 300M

The check engine light is on in my 2001 300m...the car runs great no trouble performing at stalls....runs and accelerates great .....carfax did reveal that it failed emissions 2x several years ago but it did pass this past may 2013 any tips on wat it could be? The dealer I bought it from put it on his devise and it stated no code was found....I'm stuck

Asked by for the 2001 Chrysler 300M
have the codes scanned and post so we can adv
1 more answer
if the check engine light is on it should read a code could be bad 02 sensor but I would clear the code first to see if the light comes back on