How Is a Smog Check Performed

How Is a Smog Check Performed

When a smog check is performed, a licensed technician will attach the necessary measuring equipment to your vehicle. Essentially, a smog check consists of several inspections – functional, visual, and emissions. All of these inspections validate that your emissions equipment is in check, functioning properly, and doing its job of combing out pollutants from your vehicle's exhaust.

Emissions measured, during a smog check, include oxygen (O2), hydrocarbons (HC), carbon dioxide (CO2), and carbon monoxide (CO). The emissions test also measures levels of oxides of nitrogen (Nox), in some of the nation’s most polluted urban areas.

The measurements taken, during the smog check, are recorded and immediately available to your state's agency, in charge of monitoring vehicle and smog emissions. In California, it is transmitted to the Bureau of Automotive Repair (BAR). In Georgia, data goes to the Georgia Clean Air Force (GCAF). Make some research and find information about the emission testing programs in your area.

Counties, states, or even cities, which require smog checks for DMV car registration, decide for themselves, wich testing method or combination of methods to perform. At present, several testing methods are available, including:

- On-board diagnostics (OBDI) – during this test, the required information is downloaded straight from the on-board diagnostics computer of the vehicle.

- Acceleration simulation mode (ASM) – This method is usually reserved for older vehicles and it measures emissions under simulated driving conditions, with the help of a dynamometer.

- Two-speed idle (TSI) – this test analyzes exhaust emissions from the tailpipe as the engine idles first at high, and then at low speed, and is most often reserved for older vehicles registered before 1995.

After the smog check is completed, whether it was a success or a failure, the technician will provide you with a copy of the test results, known as the Vehicle Inspection Report (VIR), along with a receipt for smog check's payment.

In case your vehicle fails the smog check, you have the option to have it repaired at a licensed smog test and repair station and after that, retest it to pass the smog check. Also, vehicles that have failed a smog check are prohibited from being driven on public roads, and if the owners are caught operating those vehicles, they will be fined.

Generally, emissions problems are not expensive and are quick to repair. If you suspect your vehicle is not going to pass a smog check, it's best to bring it to a licensed facility that can conduct the smog check and perform the necessary repairs and then have your vehicle retested to pass the smog inspection.