we have check engine light stays on on 2004 Cadillac CTS

our check engine light stays on. the diagnostic shows transmition trouble. no one can find problem. car runs fine for over a year. had sensor replaced still stays on. now we can not get our PA vehicle inspection sticker. what can the problem be?

Asked by for the 2004 Cadillac CTS
With out knowing the fault code there is no way I can help you. Please send the information for the fault code that is turning the check engine light on on your 2004 Cadillac CTS.