On most cars, the codes will read out if the engine light is on - all you have to do is put the key into the RUN position.
Normally, to get codes, you put the key on OFF and then rapidly do OFF-ON-OFF-ON-OFF-ON (on some cars you have to do four or five, not three, OFF-ON cycles). On our test 2002 car, the key did not go back to unlock, so it was ACC-ON-ACC-ON-ACC-ON.
You may have to have the parking brake firmly set for the codes to show!
Read more at http://www.allpar.com/fix/codes.html?ktrack=kcplink
just for the heck of it, check your gas cap out, you need a good seal, it can sometimes make your vehicle malfunction, if it is not tight