All about On-Board Diagnostics and Smog Checks

Back in the 1980s, the first On-Board Diagnostic system was born. The purpose of the system was to lower polluting emissions from vehicles and to assist auto repair techs with diagnosis. Since the 1980s, technological advances have occurred, so there is now a second generation system in cars that are model year 1996 or newer. This second generation system is called On-Board Diagnostics II, or simply OBD II. (There is a persistent rumor that OBD III is coming out, but alas, this is untrue.)

OBD II monitors your car’s emissions system, so that if any malfunction occurs, your Check Engine light or Service Engine Soon light will come on. The OBD II system is checked along with other emissions systems when you bring your vehicle in for a Smog Check. If a fault causes your light to be on, you will need to have the malfunction corrected and repaired before you can receive a passing score on your Smog Check.

If the technician at the Smog Check station tells you that you have too many readiness monitors that indicate that systems checks have not been completed, your vehicle may need to be driven for a few days to reset the readiness monitors to a status of Complete. Things like a disconnected or new battery or repairs on your emission system can make your readiness monitors read Non-Complete. There may be nothing wrong with your car – you just need to drive it around for a week or so to allow the self-diagnostics to reset. (If you have this situation at your biennial Smog Check in California, you should still get to the DMV and pay your registration fees and obtain a temporary operating permit to avoid late penalties.) However, if you did not recently do anything to your battery or if you do not drive the vehicle often, then you can ask the tech to help you set the flags.

Remember, the EPA considers it a federal offense to tamper with your emissions-related equipment by modifying it from a certified configuration to a non-certified one. For example, you cannot replace the catalytic converter with a straight pipe, because this would be construed as tampering. You also cannot override the OBD II system with non-certified computer chips – you can only used certified performance chips to repair the OBD II back to its original certified design.

The OBD II may fail at the time of Smog Check, even though your car may pass the tailpipe emissions portion of the check. The OBD II is designed to catch things early, even before your emissions equipment actually fails – that’s how brilliant these systems are!