San Francisco requires a smog check every two years for most vehicles, and you must pass before you can renew your registration

A smog check is an emissions test that measures whether your vehicle's exhaust meets California air quality standards. In San Francisco, you need a passing smog check to renew your vehicle registration with the Department of Motor Vehicles (DMV). The test costs between $30 and $50 at a certified smog station, and you typically get results the same day.

The requirement applies to most gasoline-powered vehicles registered in San Francisco County that are model year 1976 or newer. Diesel vehicles, motorcycles, and vehicles that are four model years old or newer have different rules. Electric vehicles do not need a smog check at all.

You can take your vehicle to any Bureau of Automotive Repair (BAR) certified smog station in California — not just in San Francisco. If your vehicle fails, you have options: repair it and retest, or in some cases dispute the results. A passing certificate is valid for 30 days, so time your test close to when you plan to renew your registration.

Key Takeaways

  • San Francisco County requires a smog check every two years for most vehicles model year 1976 or newer before you can renew your DMV registration.
  • The test costs $30 to $50 and takes about 30 minutes at a certified smog station; you get results the same day.
  • Electric vehicles, motorcycles, and vehicles four model years old or newer are exempt from the smog check requirement.
  • If your vehicle fails, you can repair it and retest, or you may be able to dispute the results through the BAR if you believe the test was wrong.
  • A passing smog certificate is valid for 30 days, so schedule your test close to your registration renewal date.

Who has to get a smog check in San Francisco

The smog check requirement in San Francisco applies to vehicles registered in San Francisco County that are model year 1976 or newer and are powered by gasoline. This covers most cars, SUVs, and light trucks on the road. The rule exists because older vehicles tend to produce higher emissions, and the test ensures they meet state air quality standards.

Several categories of vehicles are exempt. All-electric vehicles do not need a smog check because they produce zero tailpipe emissions. Motorcycles and motorized bicycles are also exempt. Vehicles that are four model years old or newer — for example, a 2021 vehicle in 2025 — do not need a smog check for their first registration renewal; they become subject to the requirement starting with the second renewal.

Diesel vehicles have a separate emissions testing program. If you own a diesel vehicle registered in San Francisco, you will need a diesel smog check instead of the standard gasoline test. The rules and testing locations differ, so confirm with a certified station whether they handle diesel vehicles.

How to find a certified smog station and what to bring

You can take your vehicle to any Bureau of Automotive Repair certified smog station in California. You do not have to use a station in San Francisco — many people use stations in nearby areas if it is more convenient. To find certified stations, search the BAR website at bar.ca.gov or call the BAR consumer hotline at 1-800-952-5210. You can also search online for "smog check near me" and filter for BAR-certified locations.

When you arrive at the station, bring your vehicle registration and a valid photo ID. The station will need your vehicle identification number (VIN), which is on your registration and on the dashboard of your car. You do not need to bring any other documents. The test itself takes about 30 minutes and involves connecting your vehicle to a machine that reads emissions data from your engine.

The smog station will give you a receipt and a certificate if you pass. Keep the certificate — you will need it when you renew your registration with the DMV. If you fail, the station will give you a detailed report showing which emissions standards your vehicle did not meet. You can use this report to decide whether to repair your vehicle or pursue other options.

What happens if your vehicle fails the smog check

If your vehicle fails the smog check, you have several paths forward. The most common is to repair the vehicle and retest. You can take your vehicle to any mechanic — not necessarily the smog station — and have them fix the emissions problem. Common repairs include replacing a faulty oxygen sensor, fixing a vacuum leak, or addressing a check engine light. Once repaired, you can return to any certified smog station for a retest.

If you believe the test result is wrong, you can request a referee smog check through the Bureau of Automotive Repair. A referee station is an independent testing facility that can review the original test and perform a new one. To request a referee check, contact the BAR directly at 1-800-952-5210 or visit bar.ca.gov. There is a fee for the referee test, typically $30 to $50, but if the referee finds that the original test was incorrect, you may be refunded.

If your vehicle repeatedly fails despite repairs, you may be may be able to access for the Smog Check information Program, which can help pay for repairs on vehicles that fail emissions tests. may be able to access depends on your household income and the vehicle's age. Contact the BAR or your local air quality management district to learn whether you may have access to.

Timing your smog check with your DMV registration renewal

A passing smog certificate is valid for 30 days from the date of the test. This means you should schedule your smog check close to when you plan to renew your registration, not months in advance. If your certificate expires before you renew, you will need to get a new smog check.

Your DMV registration renewal notice will tell you the important date for renewal. You can renew online at dmv.ca.gov, by mail, or in person at a DMV office. When you renew, you will need to provide your passing smog certificate number or submit the certificate itself, depending on which renewal method you use. If you renew online, you can enter the certificate number directly into the form.

If your registration has already expired and you did not renew on time, you can still renew it, but you will owe a late fee in addition to the registration cost. The smog check requirement does not change — you still need a passing test before the DMV will process your renewal.

Special cases: new vehicles, leased vehicles, and out-of-state transfers

New vehicles do not need a smog check for their first registration. Starting with the second registration renewal — typically two years after purchase — the smog check requirement applies. If you buy a used vehicle from a dealer in California, the dealer is responsible for providing a passing smog check before you take ownership, so you should not need to get one when ready.

If you lease a vehicle in San Francisco, the leasing company is typically responsible for maintaining the vehicle and ensuring it passes smog checks. However, you should confirm this in your lease agreement. Some leases require the lessee to handle smog checks, so read your contract carefully.

If you are moving to San Francisco from another state and registering your vehicle here for the first time, you will need a smog check before you can register it in California. This applies even if your vehicle passed emissions testing in your previous state, because California has stricter standards. Plan for the smog check as part of your registration process when you move.

Understanding what the smog check actually measures

The smog check measures three main pollutants in your vehicle's exhaust: nitrogen oxides (NOx), particulate matter, and hydrocarbons. These pollutants contribute to ground-level ozone and smog, which harm air quality and public health. The test compares your vehicle's emissions to limits set by the California Air Resources Board (CARB), which are stricter than federal standards.

For most vehicles, the test is performed using an On-Board Diagnostic (OBD) scanner, which reads data directly from your vehicle's computer. This method is fast and non-invasive — the technician plugs a device into a port under your dashboard and reads the results. Older vehicles may require a different type of test called a "two-speed idle test" or "loaded mode test," which involves driving the vehicle on a dynamometer (a machine that simulates driving).

A passing result means your vehicle's emissions are within legal limits. It does not mean your vehicle is perfectly clean or that it will not produce emissions — it means the emissions are low enough to meet California standards. If your vehicle has a check engine light on, it will typically fail the smog check, because the light indicates an emissions-related problem that needs diagnosis.

Frequently Asked Questions

Can I renew my registration without a smog check?

No. The DMV will not process your registration renewal without a passing smog check certificate, unless your vehicle is exempt. If you try to renew without one, your registration will not be approved and you will have to resubmit with the certificate.

What if I just moved to San Francisco and my vehicle passed smog in another state?

You still need a California smog check. California has stricter emissions standards than most other states, so a passing test from another state does not count. You must get a smog check in California before you register your vehicle here.

How much does a smog check cost?

A standard smog check costs between $30 and $50 at a certified station. Prices vary by location and station. If you need a referee test because you believe the original result was wrong, that also costs $30 to $50, but you may be refunded if the referee finds the original test was incorrect.

Can I get a smog check at a dealership or repair shop?

Only if the dealership or repair shop is Bureau of Automotive Repair certified. Not all shops are certified to perform smog checks. Search the BAR website or call 1-800-952-5210 to confirm that a specific shop is certified before you go.

What should I do if my vehicle fails and I cannot afford repairs?

Contact the Bureau of Automotive Repair at 1-800-952-5210 to ask about the Smog Check information Program, which may help pay for repairs if you meet income requirements. You can also contact your local air quality management district for additional resources.