What California's Smog Check Requires

California's smog check is a biennial emissions test that most vehicle owners must pass before they can renew their registration. The state runs the program through licensed testing stations — not the DMV itself — and the test measures whether your vehicle's exhaust meets California's emissions standards. You need a passing smog check certificate to complete your registration renewal, and the certificate is valid for 90 days from the test date.

The test applies to most gasoline and diesel vehicles registered in California, with some exceptions. Vehicles that are model year 1975 and older, electric vehicles, and vehicles registered as classic cars or motorcycles are exempt. Vehicles registered in certain rural counties — Alpine, Amador, Calaveras, Inyo, Madera, Mariposa, Mono, Plumas, and Tuolumne — do not require smog checks, though they still need to renew registration.

If you buy a used vehicle in California, you typically need a smog check before you can register it in your name, even if it passed recently. The seller's certificate does not transfer to you. New vehicles are exempt from smog checks for their first six years of registration.

Key Takeaways

  • California requires a smog check every two years for most vehicles, and you must pass before the DMV will renew your registration.
  • You take your vehicle to a licensed smog check station, not the DMV, and the test takes about 10 to 30 minutes depending on the vehicle type.
  • The certificate is valid for 90 days, so you can test early and complete your registration renewal within that window.
  • If your vehicle fails, you have 30 days to repair it and retest at no additional cost at the same station.
  • Vehicles model year 1975 and older, electric vehicles, and those in nine rural counties are exempt from the requirement.

Finding a Licensed Smog Check Station

California maintains a searchable database of licensed smog check stations on the Bureau of Automotive Repair website. You can search by zip code or city to find stations near you. The database shows which stations perform which types of tests — some test only gasoline vehicles, others handle diesel, and some are equipped for both.

You do not need to go to a specific station or chain. Any licensed station will perform the test and issue a certificate that the DMV accepts. Prices vary by station and region, but typically range from $30 to $70 for a basic smog check. Some stations charge extra for diesel vehicles or for retests if your vehicle fails the first time.

Before you go, call ahead to confirm the station is open and ask about wait times. Many stations operate on a walk-in basis, but some accept appointments. Bring your vehicle registration and proof of ownership.

What Happens During the Smog Check Test

The test itself is non-invasive. The technician connects a probe to your vehicle's tailpipe and measures the emissions coming out. For most vehicles, the test takes 10 to 30 minutes. The technician may also perform a visual inspection to check that your catalytic converter is present and that your emissions control system has not been tampered with.

For 1996 and newer vehicles, the technician will also plug a diagnostic scanner into your vehicle's onboard diagnostic port — usually located under the steering wheel or dashboard. This reads your vehicle's computer to check for emissions-related trouble codes. If your check engine light is on, the vehicle will likely fail this portion of the test.

You will receive a pass or fail result on the spot. If you pass, the station prints your smog check certificate when ready. If you fail, the station provides a report showing which emissions standards your vehicle did not meet and what repairs may be needed.

What to Do If Your Vehicle Fails

A failed smog check does not prevent you from driving your vehicle. It only prevents you from renewing your registration until you pass. You have 30 days from the test date to repair your vehicle and retest at the same station at no additional cost.

The repair cost depends on what failed. Common repairs include replacing a faulty oxygen sensor, fixing a vacuum leak, or replacing a spark plug wire. Some repairs are inexpensive; others can cost several hundred dollars. If the repair is expensive, you may want to get a second opinion from a mechanic before proceeding.

If you cannot afford the repair, California offers a Smog Check information Program for low-income vehicle owners. The program covers repair costs up to a certain amount — the limit varies by county. You must meet income requirements and your vehicle must have failed the smog check. Contact your county's air quality management district to learn whether your county participates and how to request help.

How to Use Your Smog Check Certificate

Once you have a passing certificate, you have 90 days to use it for your registration renewal. You can renew online through the DMV website, by mail, or in person at a DMV office. The DMV will ask for your smog check certificate number, which appears on the paper certificate the station gave you.

If you renew online or by mail, you do not need to send the physical certificate to the DMV — just provide the certificate number. If you renew in person, bring the certificate with you. The DMV verifies the certificate number in the state's smog check database to confirm it is valid and that your vehicle passed.

If your 90-day window expires before you renew, you will need a new smog check. The old certificate will no longer be accepted by the DMV.

Special Cases: Diesel Vehicles and Older Models

Diesel vehicles follow the same two-year smog check cycle as gasoline vehicles, but the test is different. Diesel smog checks measure particulate matter and opacity — how much light the exhaust blocks — rather than the same emissions standards used for gasoline vehicles. Not all smog check stations test diesel vehicles, so confirm when you call ahead.

Vehicles model year 1975 and older are exempt from smog checks statewide. Vehicles from 1976 to 1979 are exempt only if they are registered in one of the nine rural counties listed above. If you own an older vehicle and live in a county that requires smog checks, you will need to test it.

If you own a vehicle that is registered as a classic car or collector vehicle, you are exempt from smog checks. This registration type is available for vehicles at least 25 years old that are maintained in original or restored condition and driven only for exhibition or club events.

Timing Your Smog Check Around Registration Renewal

Your vehicle's registration renewal date is printed on your registration card. You can take your smog check any time in the 90 days before your renewal date. Many people test early — 60 to 90 days before renewal — to avoid the rush near the important date.

If you miss your renewal important date, your registration becomes overdue and you cannot legally drive the vehicle. You will need to renew your registration and pay a late fee in addition to the registration renewal cost. The late fee varies but is typically $50 to $100 depending on how long the registration has been expired.

If you are buying a used vehicle, the smog check requirement is separate from the registration renewal cycle. You need a smog check before you can register the vehicle in your name, regardless of when the previous owner's registration expires.

Frequently Asked Questions

Can I get a smog check waiver if my vehicle fails?

California does not issue waivers for failed smog checks. You must repair the vehicle and pass the test to renew your registration. However, if your vehicle is model year 1975 or older, or if you live in one of the nine exempt rural counties, you do not need a smog check at all.

What if I move to another state — do I still need a California smog check?

No. Once you register your vehicle in another state, California's smog check requirement no longer applies. However, you must complete your registration renewal in California before you move, or you will have an overdue registration on record.

Can I test my vehicle in a different county than where it is registered?

Yes. You can take your vehicle to any licensed smog check station in California, regardless of which county your vehicle is registered in. The test result is valid statewide.

How long does it take to get my smog check results?

You receive your pass or fail result when ready after the test is complete. The station prints your certificate on the spot if you pass. If you fail, you get a report showing what repairs are needed, and you can retest after repairs are made.

What happens if the smog check station loses my certificate?

The station's certificate number is recorded in the state's smog check database, so the DMV can verify your passing test even if you lose the paper certificate. You can request a duplicate from the station or contact the Bureau of Automotive Repair for help retrieving your certificate information.