Mission Smog Check is California's vehicle emissions testing program run by the state Bureau of Automotive Repair

Mission Smog Check is the official name of California's emissions inspection system. It tests whether your vehicle meets state air quality standards. The program is managed by the California Bureau of Automotive Repair (BAR), a division of the Department of Consumer Affairs, and administered through licensed smog check stations across the state.

Every vehicle registered in California must pass a smog check before registration renewal, with some exceptions. The test measures your vehicle's exhaust emissions — primarily nitrogen oxides, particulate matter, and hydrocarbons — to may support they fall within legal limits. If your vehicle fails, you have options for repair and retesting before you can renew your registration.

The program exists because California has stricter air quality standards than federal law requires. The state's geography and climate make air pollution a persistent problem, so the smog check is one tool to reduce emissions from the vehicle fleet.

Key Takeaways

  • California requires a smog check every two years for most vehicles, or annually for vehicles over 8 years old in some cases.
  • You must pass the test before you can renew your vehicle registration with the DMV.
  • Only licensed smog check stations can perform the test — you cannot do it yourself or at an unlicensed shop.
  • If your vehicle fails, you have 30 days to repair it and retest at no additional fee at the same station.
  • Certain vehicles are exempt, including those under 4 years old, electric vehicles, and some motorcycles.

When you need a smog check and which vehicles are exempt

You need a smog check before you renew your vehicle registration in California. The timing depends on your vehicle's age and type. Most vehicles require a test every two years. Vehicles registered in California for the first time may need a smog check before initial registration, depending on the vehicle's age and model year.

Several categories of vehicles do not need a smog check. Vehicles less than 4 years old are exempt. All-electric vehicles and plug-in hybrids are exempt. Motorcycles registered as motorcycles (not as vehicles) are exempt. Vehicles with a gross vehicle weight rating over 14,000 pounds are exempt. If you are unsure whether your vehicle qualifies for an exemption, the California DMV website lists the full criteria, or you can ask a smog check station.

Vehicles that fail a smog check can be retested within 30 days at the same station without paying the test fee again. However, you must pay for any repairs yourself. If your vehicle fails a second time, you may be able to request a referee smog check — a more thorough test performed by a BAR referee station — to determine whether the vehicle can be brought into compliance.

How to find a licensed smog check station

You can locate a licensed smog check station through the California Bureau of Automotive Repair's official station locator on the BAR website. Enter your zip code or city to see stations near you. The locator shows the station's address, phone number, and hours. You can also search "smog check near me" in a search engine, but verify the station's license through the BAR locator before you go.

Licensed stations display a BAR license certificate in the window. The certificate shows the station's license number and expiration date. If a station does not display this certificate or cannot provide a license number, do not use it — unlicensed testing is illegal and your results will not be accepted by the DMV.

Call ahead to ask about wait times and pricing. Smog check fees vary by station and vehicle type, typically ranging from around $30 to $70 for a basic test. Some stations charge more for vehicles with check engine lights or for additional diagnostic work. Ask whether the station offers a retest at no charge if your vehicle fails.

What happens during a smog check test

A smog check test takes 10 to 30 minutes depending on your vehicle's age and type. For most vehicles, the technician will connect your vehicle to an emissions analyzer, which measures tailpipe emissions. The analyzer checks for carbon monoxide, hydrocarbons, nitrogen oxides, and particulate matter. Your vehicle must meet California's emission standards for its model year.

Vehicles 1975 and older, and some vehicles between 1976 and 1995, may receive a visual inspection instead of a tailpipe test. The technician checks that emissions control equipment is present and appears functional. Vehicles 1996 and newer typically receive an On-Board Diagnostic (OBD) test, which reads data from your vehicle's computer. The OBD test checks whether the check engine light is on and whether your vehicle's emissions systems are working as designed.

You will receive a printed smog check certificate when ready after the test. If you pass, the certificate shows your vehicle's test results and is valid for 30 days. You must present this certificate to the DMV when you renew your registration. If you fail, the certificate will list the emission standards your vehicle did not meet and recommend repairs.

What to do if your vehicle fails the smog check

If your vehicle fails, you have 30 days to repair it and return to the same station for a retest. The retest is free if you use the same station. The station must provide you with a written explanation of why your vehicle failed and what repairs may fix the problem. However, the station is not required to perform the repairs — you can take your vehicle to any repair shop you choose.

Common reasons for failure include a faulty oxygen sensor, a malfunctioning catalytic converter, a loose gas cap, or a check engine light that is on. Some repairs are inexpensive; others can cost several hundred dollars. Before you authorize major repairs, ask the shop for a written estimate and consider getting a second opinion if the cost is high.

If your vehicle fails twice, you may request a referee smog check. A referee station is operated by the BAR and performs a more detailed test to determine whether your vehicle can meet standards with repairs. To request a referee test, contact the BAR directly or ask your smog check station for the referee station nearest you. The referee test costs more than a regular test but can help you understand whether repair is possible.

Understanding your smog check certificate and registration renewal

Your smog check certificate is a separate document from your vehicle registration. It is valid for 30 days from the test date. You must bring the original certificate to the DMV or submit it online when you renew your registration. If your certificate expires before you renew, you will need a new smog check.

The DMV will not process your registration renewal without a passing smog check certificate, unless your vehicle is exempt. You can renew your registration online, by mail, or in person at a DMV office. When you renew, you will pay registration fees plus any smog check fee if you have not already paid it at the testing station.

If you move out of California or sell your vehicle, you do not need to complete a smog check for that vehicle. However, if you buy a used vehicle in California, the seller must provide a smog check certificate dated within the last 30 days, or the vehicle must be exempt.

What the smog check results mean

A passing smog check means your vehicle's emissions are within California's legal limits for its model year. Older vehicles have less strict standards than newer ones, so a 2005 vehicle has different emission limits than a 2020 vehicle. Passing does not mean your vehicle is "clean" in an absolute sense — it means it meets the state's minimum requirement.

A failing result shows which emission standards your vehicle exceeded. The certificate will list the specific pollutants — such as nitrogen oxides or hydrocarbons — that were too high. This information helps a repair technician diagnose the problem. For example, high nitrogen oxides often point to a faulty oxygen sensor or EGR valve, while high hydrocarbons may indicate incomplete fuel combustion.

If your vehicle has a check engine light on, it will fail the OBD test automatically. The light indicates that your vehicle's onboard diagnostic system has detected a problem. You must have the vehicle scanned with a diagnostic tool to read the error code and determine what repair is needed. Many repair shops offer free or low-cost diagnostic scans.

Frequently Asked Questions

Can I get a smog check waiver if my vehicle is old or has a high repair cost?

California offers a Smog Check Referee Program for vehicles that fail twice. If a referee determines your vehicle cannot be repaired to meet standards, you may be issued a waiver that allows you to register the vehicle for one year. However, waivers are not automatic — the referee must document that repairs are not feasible or cost more than the vehicle's value.

What if I just bought a used car and the smog check certificate is expired?

You will need a new smog check before you can register the vehicle in your name. The seller's certificate is only valid for 30 days from the test date. If it has expired, you must pay for a new test at a licensed station. Ask the seller whether they will cover the cost, as some do.

Do I need a smog check if my vehicle is registered out of state?

If you move to California and register a vehicle that was previously registered out of state, you will need a smog check before initial California registration, unless the vehicle is exempt. The vehicle must be tested at a California licensed station. Vehicles registered in other states do not need California smog checks.

Can a smog check station refuse to test my vehicle?

Yes. A station can refuse to test a vehicle if it is unsafe to drive, if the check engine light is on and the station cannot read the code, or if the vehicle is not registered. If a station refuses, ask why and get the reason in writing. You can then take the vehicle to another station or to a repair shop to fix the problem first.

How much does a smog check cost?

Fees vary by station and vehicle type, typically between $30 and $70 for a standard test. Some stations charge more for vehicles with check engine lights or for additional diagnostics. Call ahead to ask the price. The fee is separate from any repair costs if your vehicle fails.