Your Check Engine light signals both problems that could cause engine failure or a required maintenance interval. OBD scanners and code readers pull trouble codes from the vehicle's computer to help determine what may have caused the light to come on. These tools can take the guesswork out of reading and clearing Check Engine light codes on most models. Keep in mind that vehicles made since 1996 require an OBD-II reader, but some scan tools are able to read both OBD and OBD-II codes. O'Reilly Auto carries OBD scan tools and code readers to help make your diagnosis easier.