What Happens During A Smog Check?

Smog check

During a smog check, a licensed technician will attach measuring equipment to your vehicle. The smog check test consists of Emissions Inspection, Visual Inspection and Functional Inspection--all of which ensure your emissions equipment is in place, functioning, and doing its job of weeding out pollutants from your car's exhaust.

Emissions measured include carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC) and oxygen (O2). In some of the nation’s most polluted urban areas, the emissions test also measures levels of oxides of nitrogen (NOx).

During the smog check, the measurements taken are recorded and immediately available to your state’s agency responsible for monitoring smog and vehicle emissions. In Georgia, data goes to the Georgia Clean Air Force (GCAF). In California, it is transmitted to the Bureau of Automotive Repair (BAR). For more information on emission testing programs in other states, click here.

Cities, states and counties that require smog and emissions tests for DMV car registration determine which testing method or combination of methods to use. Current testing methods include:

  • 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 usually for older cars registered before 1995.
  • Acceleration simulation mode (ASM) – Again, most often reserved for older vehicles, the ASM test measures emissions under simulated driving conditions using a dynamometer.
  • On-board diagnostics (OBDI) – During this test, information is downloaded from the vehicle’s on-board diagnostics computer.

Following completion of the smog check, whether pass or fail, the technician will give you a copy of the test results, called the Vehicle Inspection Report (VIR), along with a receipt for payment of the smog check.

If your vehicle fails the smog check, you can choose to have it repaired at a licensed test and repair station and then have it retested to pass the smog check. Vehicles that have not passed inspection are not allowed on public roads and owners will be ticketed if they are caught operating those vehicles.

Emissions problems are generally inexpensive and quick to repair. If you believe your vehicle won’t pass a smog check, it may be best to go to a facility that can perform the check and make any necessary repairs and then re-test so the vehicle passes smog inspection.

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