How California's emissions test works

California's emissions test, officially called the Smog Check, measures whether your vehicle's exhaust meets state air quality standards. The test itself takes about 10 to 15 minutes and costs between $30 and $70 depending on your vehicle type and the testing station. You drive onto a dynamometer (a machine that simulates road conditions), and technicians measure what comes out of your tailpipe — primarily nitrogen oxides, particulate matter, and hydrocarbons.

The state requires this test for most vehicles registered in California, with some exceptions for very new cars and electric vehicles. If your vehicle passes, you receive a certificate valid for two years. If it fails, you have 30 days to repair it and retest at no additional cost, or you can take it to a different station for a second opinion.

The test is tied directly to your vehicle registration renewal. You cannot renew your registration without a passing Smog Check certificate, and the Department of Motor Vehicles (DMV) will not issue your registration until the certificate is in their system.

Key Takeaways

  • California requires a Smog Check every two years for most vehicles, and you cannot renew your registration without a passing certificate.
  • The test costs $30 to $70 and takes 10 to 15 minutes at a licensed testing station, which you can find through the Bureau of Automotive Repair website.
  • If your vehicle fails, you have 30 days to repair it and retest at no charge, or you can get a second opinion at another station when ready.
  • Vehicles from the current model year and the previous four model years are exempt, as are all battery electric vehicles and hydrogen fuel cell vehicles.
  • Repairs needed to pass the test are your responsibility, but you can shop around — the test itself is standardized, but repair costs vary widely.

When you need to take the test

You need a Smog Check before you renew your vehicle registration. The timing depends on when your registration expires. If your registration expires in June, you need the test by June. You can take the test up to 60 days before your registration expires, so you have a window to plan ahead.

New vehicles are exempt for the first six years of ownership (the current model year plus the previous five). After that, the test becomes required every two years. If you buy a used vehicle that has not been registered in California before, you will need a Smog Check before you can register it here, even if it just passed in another state.

Vehicles registered outside California do not need a Smog Check until they are re-registered in California. If you move to California with an out-of-state vehicle, you have 20 days to register it; the Smog Check must be done before registration is complete.

Which vehicles are exempt

Battery electric vehicles (BEVs) and hydrogen fuel cell vehicles are permanently exempt from Smog Check requirements. Plug-in hybrids are not exempt and must pass the test.

Gasoline and diesel vehicles are exempt if they are from the current model year or any of the previous four model years. For example, in 2024, vehicles from model years 2020 through 2024 are exempt. Once your vehicle reaches model year 2019 or older, it becomes subject to the test.

Motorcycles, trailers, and vehicles with a gross vehicle weight rating over 14,000 pounds follow different rules. Motorcycles have their own emissions standards and testing procedures. Heavy trucks and commercial vehicles may be subject to different testing through the California Air Resources Board (CARB) Heavy-Duty Inspection and Maintenance Program.

Finding a testing station and what to bring

The Bureau of Automotive Repair (BAR) maintains a searchable list of licensed Smog Check stations on their website at bar.ca.gov. You can search by zip code or city. All licensed stations use the same test procedure and equipment, so the test results are consistent regardless of which station you choose. However, prices vary, so calling ahead to ask the cost is worth your time.

Bring your vehicle registration or proof of ownership, a valid photo ID, and your vehicle keys. Some stations may ask for your Vehicle Identification Number (VIN) before you arrive. If your vehicle has failed before, bring documentation of any repairs you have had done — this is not required, but it can help if there is a dispute about the results.

Your vehicle should be in normal operating condition. Do not arrive with a check-engine light on unless you have already had it diagnosed and repaired; the test will fail if the light is illuminated. Warm up your engine for a few minutes before the test, as a cold engine can produce higher emissions readings.

What happens if your vehicle fails

If your vehicle fails the Smog Check, you receive a detailed report showing which emissions standards it did not meet. Common failure reasons include a faulty oxygen sensor, a malfunctioning catalytic converter, a clogged air filter, or an engine control issue. The report will not tell you exactly what is wrong — that is a mechanic's job — but it will tell you which emissions category failed.

You have 30 days from the test date to repair your vehicle and retest at the same station at no charge. If you use a different station for the retest, you will pay the testing fee again. Many people get a second opinion at a different station when ready after a failure, which costs another $30 to $70 but can confirm whether the failure is real or a testing error.

Repair costs depend entirely on what is wrong. A new oxygen sensor might cost $150 to $300 installed. A catalytic converter replacement can run $800 to $2,500. An air filter is $20 to $50. Get quotes from at least two repair shops before committing, and ask whether they offer a warranty on the repair work.

Repair information and cost-sharing programs

California offers the Enhanced Fleet Modernization Program (EFMP) and the Consumer information Program (CAP), which can help pay for repairs if your vehicle fails the Smog Check and you meet income requirements. These programs are administered through the California Air Resources Board and local air districts.

EFMP focuses on older vehicles and can provide up to $9,500 toward repairs or vehicle replacement if your household income is at or below 400 percent of the federal poverty line. CAP provides up to $1,500 in repair information for lower-income households. may be able to access varies by county and program, and funding is limited.

Contact your local air quality management district to learn whether these programs are currently taking new participants in your area. You can find your district through the CARB website. Some districts have waiting lists, and some programs run out of funding partway through the year.

Preparing your vehicle before the test

Basic maintenance before your test can reduce the chance of failure. Check your engine oil level and top it off if needed — low oil can trigger emissions issues. Replace your engine air filter if it is visibly dirty; a clogged filter restricts airflow and increases emissions. Make sure your gas cap is tight; a loose or missing cap can cause a check-engine light and automatic failure.

If your check-engine light is on, have the code read at an auto parts store (many do this for free) before you test. Some codes are minor and straightforward to fix; others indicate a serious problem. Do not ignore the light and hope it goes away — the Smog Check will catch it.

Drive your vehicle normally for a few days before the test. A vehicle that has been sitting idle or driven only short distances may not be in optimal condition for testing. Highway driving helps clear out the fuel system and can improve emissions readings.

Frequently Asked Questions

Can I test my vehicle before my registration expires?

Yes. You can take the Smog Check up to 60 days before your registration expires. The certificate is valid for two years from the test date, so if you test early, your certificate will remain valid even after your current registration expires.

What if I move out of California after I pass the test?

Your California Smog Check certificate is only valid in California. If you move to another state, you will need to follow that state's emissions testing rules, which may be different or nonexistent. The certificate does not transfer.

Do I need a Smog Check if I am selling my vehicle to someone else?

No. The seller does not need to provide a passing Smog Check. However, the buyer will need one before they can register the vehicle in California. Some buyers ask sellers to provide a recent test result as proof of condition, but this is not required by law.

What if the testing station says my vehicle cannot be tested?

Some vehicles cannot be tested on a standard dynamometer — for example, vehicles with very low ground clearance or certain all-wheel-drive systems. The station will refer you to a different testing facility equipped to handle your vehicle type. This is rare, but if it happens, the station will provide you with a referral.

Can I dispute my test results?

Yes. If you believe the test was performed incorrectly, you can request a retest at a different station. You pay the testing fee again, but if the second test passes, you can file a complaint with the Bureau of Automotive Repair about the first station. Keep your test paperwork from both stations if you do this.