What the California Smog Check requires

California's Smog Check is a biennial (every two years) or annual emissions test that measures whether your vehicle's exhaust meets state pollution standards. Most vehicles registered in California must pass this test to renew their registration. The test itself takes about 10 minutes and costs between $30 and $50 at a certified station.

You need a Smog Check before you can renew your vehicle registration with the California Department of Motor Vehicles (DMV). The test result is valid for 30 days, so you can take it up to a month before your registration expires. If you fail, you have 30 days to repair the vehicle and retest at no additional charge at the same station.

Key Takeaways

  • Most California vehicles need a Smog Check every two years, though some newer or older vehicles follow different schedules.
  • The test measures nitrogen oxides, particulate matter, and other emissions through your vehicle's onboard diagnostic system or tailpipe.
  • You must pass before renewing registration, and the test result is valid for 30 days.
  • If you fail, you can retest free of charge within 30 days at the same station after repairs.
  • Vehicles that fail twice in a row may be subject to a referee inspection, which costs more and involves a state official.

Which vehicles need testing and when

Most passenger cars, light trucks, and SUVs registered in California need a Smog Check every two years. However, the schedule depends on your vehicle's model year and type. Vehicles model year 1975 and older are exempt. Vehicles model year 1976 through 1999 need testing every two years. Vehicles model year 2000 and newer need testing every two years as well, but some very new vehicles (typically model year 2023 and newer) may be exempt for their first few years.

Diesel vehicles have their own rules. Light-duty diesel vehicles (under 14,000 pounds) follow the same two-year schedule as gasoline vehicles. Heavy-duty diesel vehicles and commercial trucks follow different testing requirements through the Heavy-Duty Vehicle Inspection Program.

Motorcycles, motorhomes, and vehicles registered as non-operational are exempt. If you buy a used vehicle in California, you must pass a Smog Check before you can register it in your name, even if it just passed in another state.

How the test works and what it measures

The Smog Check has two main formats depending on your vehicle's model year. Vehicles model year 1996 and newer use the OBD-II test, which reads data directly from your vehicle's onboard diagnostic computer. The technician plugs a scanner into the diagnostic port (usually under the steering wheel) and checks whether your vehicle's emissions control systems are functioning. This test takes about five minutes and does not require you to drive on a dynamometer.

Vehicles model year 1995 and older use the two-speed idle test or loaded mode test. The two-speed idle test measures exhaust at idle and at 2,500 RPM. The loaded mode test runs your vehicle on a dynamometer (a treadmill for cars) while measuring tailpipe emissions. These tests check for nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC).

You pass if your vehicle's emissions fall below the state limits for your model year. The limits are stricter for newer vehicles. If your check engine light is on, you will fail the OBD-II test regardless of actual emissions, because the light indicates a fault in the emissions control system.

Finding a certified test station and scheduling

You can test at any station certified by the California Bureau of Automotive Repair (BAR). The official BAR station locator is available at the California DMV website. You can search by ZIP code or city. Most stations are independent repair shops, not dealerships, though some dealerships also perform Smog Checks.

You do not need an appointment at most stations, but calling ahead can save you a wait, especially during peak times (late in the month when registrations are expiring). Bring your vehicle registration and a valid ID. The test takes 10 to 20 minutes total, including paperwork.

If you fail, you can return to the same station for a free retest within 30 days. If you fail a second time, you may be referred to a referee station for a third test. Referee stations are run by the state and charge a higher fee (typically $70 to $100). A referee test is more thorough and is binding — if you pass a referee test, your vehicle is cleared for registration even if it failed the first two tests.

What happens if you fail and repair options

If you fail, the station will provide a detailed report showing which emissions exceeded limits. For OBD-II vehicles, the report will show which diagnostic codes are present. For older vehicles, the report will show specific pollutant levels.

Common reasons for failure include a faulty oxygen sensor, a loose gas cap, a failing catalytic converter, or a malfunctioning emissions control valve. Many of these repairs cost $100 to $500. Some repairs are more expensive — a catalytic converter replacement can run $800 to $2,000 depending on your vehicle.

You have 30 days to repair and retest at no charge. If you cannot afford repairs, California offers the Consumer information Program (CAP), which provides up to $500 toward emissions-related repairs for vehicles owned by low-income drivers. You must meet income limits and own a vehicle model year 2000 or older. Contact your local air quality management district to learn about CAP in your area.

Registration and penalties for not testing

You cannot renew your vehicle registration without a passing Smog Check result. When you renew at the DMV (online, by mail, or in person), you must provide your test station's certification number or submit the test result directly. If you renew online or by mail, the DMV will verify the result electronically.

If you drive with an expired registration because you have not passed a Smog Check, you can be cited. The penalty is typically a fine of $250 or more. Driving with a significantly expired registration can also result in vehicle impound in some cases.

If you move out of California, you do not need a Smog Check to cancel your registration. If you move to another state and return to California later, you will need to pass a Smog Check before registering your vehicle again.

Frequently Asked Questions

Can I pass a Smog Check if my check engine light is on?

No. If your check engine light is illuminated, you will fail the OBD-II test automatically, even if your actual emissions are within limits. The light indicates a fault in your emissions control system. You must have the fault diagnosed and repaired, then the light must be cleared before you can pass.

What if I just bought a used car and it failed Smog Check?

You have 30 days to repair and retest. If the vehicle was sold to you as already passing, you may have a claim against the seller under California's used vehicle lemon law, though this depends on the specific circumstances. Contact the California Department of Consumer Affairs if you believe you were sold a vehicle that cannot pass.

Do I need a Smog Check if I only drive my car occasionally?

Yes, if your vehicle is registered in California, you need a passing Smog Check to renew registration every two years, regardless of how often you drive it. The only exception is if your vehicle is registered as non-operational or exempt by model year.

How long does a Smog Check result stay valid?

Your test result is valid for 30 days. You must submit it to the DMV within that window to renew your registration. If the result expires before you renew, you will need to retest.

What if I fail twice and get sent to a referee station?

A referee station conducts a more detailed inspection and charges a higher fee. If you pass the referee test, your vehicle is cleared for registration. If you fail the referee test, you may be subject to additional requirements or restrictions depending on your vehicle's condition and your local air district's rules.