What is Checked During an Emissions Test

What is Checked During an Emissions Test?

Starting with the 1966 model year, California began requiring emissions control systems, catalytic converters, on cars sold in California. This was adopted across the United States in 1968, and eventually became the Clean Air Act of 1970.

Many states have mandatory emissions inspections in all or some counties which is typically done as part of the car registration or registration renewal process. Up until 2000, that meant popping the car on a dyno, sticking a sniffer in the tailpipe and measuring what percentage of the air coming out of the vehicle was clean. But in 2000 the EPA started pushing an OBD-II emissions test and many states adopted it, or are in the process of adopting it.

Instead of sticking a sniffer in the tailpipe, the emissions computer is plugged into the OBD-II port on the vehicle. This is usually located under the dash or hidden behind the cigarette lighter. The emissions computer then asks the vehicle?›ƒ?ªƒ?›s computer whether the emissions equipment is working within the required efficiency limits. This is much more efficient than using the old sniffer method.

The way the OBD-II tests works is pretty simple. The vehicle?›ƒ?ªƒ?›s engine control unit (ECU) waits for a set of conditions that are representative of normal driving conditions and then checks the values of a few sensors to make sure the equipment is working properly. Typically, it examines the catalytic converter, the Exhaust Gas Recirculation, and the evaporative emissions. The inspection machine also checks the computer to see if any error codes are set, and if the check engine light is set. If the tester determines the emissions equipment is in order, the vehicle is passed without needing any further emissions related tests.

If the vehicle is inspected while it is not ready, the vehicle will return a not ready message to the inspection computer. The typical remedy for failing readiness is to drive the vehicle around for up to five hundred miles and then to try the test again. After that, if the vehicle still fails, a dealer or shop with factory diagnosis equipment is required to force the vehicle to run the emissions tests regardless of readiness.

If your vehicle needs an exhaust system repair, let our knowledgeable technicians take care of you. Contact us at Jack?›ƒ?ªƒ?›s Tire & Oil for an appointment, or stop by and let us take a look.


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