Smog Check: Obtaining a California Smog Certificate

By David Sturtz, April 16, 2008

Why Do We Need Smog Checks?

The federal Clean Air Act (passed in 1970 and amended in 1990) mandates air pollution and air quality standards. More than 50 percent of air pollution is caused by motor vehicles. Yet only 10 to 15 percent of cars are responsible for that 50 percent.

Some areas of California exceed the federally mandated air pollution guidelines. California's Smog Check Program concentrates on "nonattainment" areas of the state—that is, areas where air pollution is above federal guidelines. Commonly the more populated areas of the state.

mechanic explaining to customer

What Happens During a Smog Check?

Motor vehicles are inspected and, if needed, maintenance is performed to bring them into compliance. This is where the term I and M (inspection and maintenance) comes from

Vehicles are tested on an Emissions Inspection System (EIS). The system measures the chemicals in a vehicle's tail pipe emissions under various conditions, such as at different speeds and bearing different loads. The most common auto pollutants are carbon monoxide (CO), nitrous oxide (NO), and hydrocarbons (HCs). If the test shows any of these chemicals to be outside federal and state guidelines, the vehicle fails the smog check.

To verify that nothing has been removed or modified in the emission control system and that everything is in good working order, various other visual inspections and functional tests are performed. If the vehicle does not pass the visual or functional part of the smog check, the vehicle fails.

Who Needs a Smog Check?

Smog inspections are required unless your vehicle is:

  • Six years old or newer
  • 1975 model or older
  • Diesel powered 1997 model year and older or with a Gross Vehicle Weight ratting (GVWR) of more than 14,000 lbs.
  • Electric
  • Natural Gas Powered with a GVWR of more than 14,000 lbs.
  • A hybrid
  • A Motorcycle
  • A Trailer

Stations Types

  • STAR station: All types of vehicles needing a smog inspection can be tested at these stations.
  • Test only station: Smog inspections can be performed on all vehicles not directed to a STAR station as indicated on the renewal notice or smog failure printout. These stations are not allowed to perform emission related repairs.
  • Repair Only Station: Can perform smog related repairs but cannot issue a certificate upon completion of repairs.

What Are My Choices if My Vehicle Fails?

  • You may have the vehicle repaired at any Smog Check Star or Repair Only station at your expense, but the vehicle must be re-certified and pass at either a Test Only or Star station as directed.
  • You may retire or have the vehicle repaired at a Smog Check STAR station with assistance from the Consumer Assistance Program (CAP).
  • If you have invested a minimum of $650 in diagnostics and repair (either out-of-pocket or through CAP), you can choose to pay the additional money needed to bring the vehicle into compliance or take the vehicle to a State of California Referee Center.
  • If the vehicle emissions system has been tampered with, cost limits listed above may not apply.

Parts Availability Repair Waiver

In any of the above failure cases, if the parts needed to bring the vehicle into compliance are not available, you may apply for a referee-approved parts availability waiver. Take the vehicle to a referee station and verify through documentation that the needed parts to repair the vehicle are not available. You can then receive up to a two-year waiver on repairing the vehicle, and the vehicle will be smog certified during the allotted time period.

1 User Comment

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By , January 16, 2011
CA "smog check", is designed to manufacture NOx failures especially on economy cars. Go to for Smog test failure help.

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