There isn't a field test for checking you for codeine. Now..if you're involved in an auto-accident, the hospital would certainly check your blood and it might turn up (depending on your last usage). Not sure what your question is about? Are you on some type of court-ordered supervision?

The only people who "get in trouble" for having codeine in their system or on their person/(car) is if you have a dirty U.A. with your probation/parole unit, do not have a prescription for it, violate the terms of your probation/parole, LE finds it and/or is involved in some type of criminal offense (Selling or DUI accident/altercation).