What a smog test is and why California requires it
A smog test, also called a smog check, is an emissions test that measures how much pollution your vehicle produces. California requires it because the state has air quality standards set by the Environmental Protection Agency, and vehicles are a major source of the pollution that makes meeting those standards difficult.
The test itself is straightforward: a technician plugs a diagnostic machine into your vehicle's onboard computer port, reads the emissions data, and checks whether your vehicle meets California's limits. The whole process usually takes 10 to 15 minutes. If your vehicle passes, you get a certificate. If it fails, you receive a report showing what needs repair.
California divides the state into air quality regions, and the rules vary by region. The South Coast Air Quality Management District (SCAQMD), which covers Los Angeles, Orange County, San Bernardino, and Riverside counties, has stricter standards than some other regions because the air quality there is worse. If you live in that region, your vehicle may fail a test that would pass elsewhere in the state.
Key Takeaways
- California requires a smog test every two years for most vehicles, or every year if your vehicle is model year 1975 or older.
- The test measures emissions from your vehicle's engine and must be performed by a Bureau of Automotive Repair-certified technician at a smog station.
- You can find certified smog stations through the California Bureau of Automotive Repair website or by searching for "smog check" in your area.
- If your vehicle fails, you have 30 days to repair it and retest at no additional charge at the same station.
- The cost varies by region and station, but typically ranges from $30 to $70 for the test itself.
When you need a smog test in California
You need a smog test when you renew your vehicle registration with the California Department of Motor Vehicles (DMV). For most vehicles, this happens every two years. If your vehicle is model year 1975 or older, you need the test every year. Vehicles model year 1976 and newer that are less than four years old are exempt from smog testing.
The DMV will not renew your registration without proof that your vehicle passed the test. You do not have to get the test done before you go to the DMV — you can do it anytime during your registration renewal period — but you must have the passing certificate before the DMV will process your renewal.
If you are buying a used vehicle in California, the seller must provide you with a smog certificate dated within 90 days of the sale. This is separate from your regular smog test schedule; it is a one-time requirement for the purchase.
Where to get a smog test and what it costs
You can get a smog test at any station certified by the California Bureau of Automotive Repair (BAR). These include independent smog stations, some gas stations, some repair shops, and some dealerships. The Bureau maintains a searchable database on its website where you can enter your zip code and find certified stations near you.
The cost of the test itself is set by each station and varies by region. In most areas, you can expect to pay between $30 and $70. Some stations charge extra if your vehicle has a diesel engine or is a heavy-duty vehicle. Ask the station for the price before you bring your vehicle in.
When you arrive, bring your vehicle registration or proof of ownership and your vehicle's keys. The technician will plug a diagnostic scanner into your vehicle's onboard diagnostic port (usually located under the steering wheel or dashboard) and run the test. The whole process takes 10 to 15 minutes.
What happens if your vehicle fails the smog test
If your vehicle fails, the technician will give you a detailed report showing which emissions standards your vehicle did not meet. Common reasons for failure include a faulty oxygen sensor, a malfunctioning catalytic converter, a loose gas cap, or an engine problem that triggers the check-engine light.
You have 30 days from the test date to repair your vehicle and return to the same station for a retest at no additional charge. If you repair it at a different shop, you can still retest at the original station. Keep your repair receipts — some programs offer repair cost information if your vehicle fails and you cannot afford the repairs.
If you cannot afford the repairs, look into the California Consumer information Program (CCAP), which provides repair cost information to low-income vehicle owners whose vehicles fail the smog test. You can find information about CCAP through the Bureau of Automotive Repair website or by contacting your local air quality management district.
Understanding the South Coast Air Quality Management District rules
If you live in Los Angeles, Orange County, San Bernardino, or Riverside counties, your vehicle is tested under South Coast AQMD standards, which are stricter than California's statewide standards. This means your vehicle may fail a smog test in this region even if it would pass elsewhere in California.
The South Coast AQMD has these stricter rules because the air quality in Southern California is historically worse than in other parts of the state. The region has more vehicles, more traffic congestion, and geography that traps pollution. The stricter emissions standards are designed to improve air quality in the region.
If you live in the South Coast AQMD region and your vehicle fails, the repair requirements may be more extensive than they would be in another region. The technician's report will show you exactly what needs to be fixed to meet the regional standard.
How to prepare your vehicle for a smog test
Before you take your vehicle in for a smog test, make sure the check-engine light is not on. If it is, have the vehicle scanned for trouble codes before the test. Many smog stations will do this scan for a small fee, or you can visit a repair shop. A check-engine light almost always results in a test failure.
Make sure your gas cap is tight and not damaged. A loose or faulty gas cap is one of the most common reasons for smog test failure and is also one of the cheapest and easiest fixes. If your gas cap is cracked or does not seal properly, replace it before the test.
If your vehicle has not been driven recently, take it for a 15 to 20 minute drive on the highway before the test. This warms up the engine and the catalytic converter, which can improve test results. Avoid taking the test when ready after starting a cold engine.
What your smog test certificate means and how long it lasts
A passing smog test certificate is valid for 90 days from the test date. You must present this certificate to the DMV when you renew your vehicle registration. If your registration renewal period ends before the 90 days are up, you can take the test anytime during the renewal period and still use the certificate.
The certificate shows the test date, your vehicle's information, the emissions readings, and the technician's signature. Keep a copy for your records. The DMV will keep a copy on file when you renew your registration.
If you pass the test but do not renew your registration right away, you do not have to take the test again as long as you renew before the 90-day certificate expires. However, if your registration expires and you let it lapse, you will need a new smog test when you eventually renew.
Frequently Asked Questions
Can I take a smog test at any time, or does it have to be during my registration renewal period?
You can take the test anytime, but the certificate is only valid for 90 days. If you take it too early in your renewal period, the certificate may expire before you renew your registration. Most people take the test within a month of their registration renewal date to avoid this problem.
What if I just bought a used car and the seller did not give me a smog certificate?
The seller was required by law to provide one dated within 90 days of the sale. Contact the seller and ask for it. If the seller refuses or cannot provide it, you will need to get a new smog test before you can register the vehicle in your name.
Do I need a smog test if I just moved to California from another state?
Yes. When you register your vehicle in California for the first time, you will need a smog certificate. The only exception is if your vehicle is less than four years old, in which case you are exempt from the test for the first registration in California.
What if my vehicle is a hybrid or electric vehicle?
Hybrid vehicles still require a smog test because they have a gasoline engine. Electric vehicles are exempt from smog testing because they produce no emissions. When you register an electric vehicle in California, you will not need a smog certificate.
Can I get a smog test waiver if my vehicle is old or has high mileage?
California does not offer waivers based on age or mileage alone. However, if your vehicle fails the test and repairs would cost more than a certain percentage of the vehicle's value, you may be able to get a waiver. The percentage varies by region. Ask the smog station or your local air quality management district about waiver programs.