Obd ii check engine light trouble codes welcome to obd codescom your headquarters for everything obd ii related for more information on what obd codes are obd ii codes explained explanation of fuel trims or answers to other questions visit our faq area the most common obd ii codes are p0 powertrain codes which are linked below on this page along with p2 generic p3 . Diagnostic trouble codes or fault codes are obd2 codes that are stored by the on board computer diagnostic system these are stored in response to a problem found in the car by the system these obd2 codes are stored when a sensor in the car reports a reading that is outside the normal accepted range eg fuel mixture too rich. On board diagnostic obd trouble codes are one way your vehicle communicates with a mechanic every car built since 1996 has an obd computer system that monitors and identifies issues in particular it looks for issues that may result in harmful and polluting emissions from exhaust gases. With an obd reader or a scanner youll be able to access your cars obd ii codes but may not be able to understand them as this depends on the model you own if your obd tool doesnt offer dtc definitions dont fret well cover everything you need to know right here. Trouble codes check engine light trouble codes for old and new cars and trucks some vehicle specific codes full list of obd ii diagnostic trouble codes if your check engine light is on you may have a serious problem scan your codes and follow the chart to determine what the code means some parts stores will scan your codes for free