California Smog Check Requirements

What is a smog test?

Smog testing is essentially an inspection of your vehicle’s exhaust system to determine if it meets the state’s emissions standards. Smog tests are required on a regular basis in California, but they are not required in all states. Don’t be alarmed if you fail one; there are several potential fixes for every type of vehicle.

How do car modifications affect smog tests?

To pass a smog test, your vehicle must have a certain level of emissions, and many aftermarket modifications can interfere with this. The following modifications may have an impact on your vehicle’s emissions:

Catalytic converters in the exhaust system
Engine tuning or alterations
Aftermarket air intake modifications (i.e., replacing the stock air filter with a larger one)

You may be wondering if you should use your vehicle’s “stock” settings when having it tested. It is critical that you only use equipment and settings that are permitted by state law. California does not require vehicles to use any special equipment during a smog check, only that they do not emit excessive amounts of pollution.

Failing the smog test

If your car doesn’t pass the smog test, you’ll be given a list of issues that need to be repaired. There are some stipulations to this, though: if the total cost of repairs exceeds $450—or $650 for a hybrid or electric vehicle—the state may waive the repairs and pay you up to $500 instead.

Once your car has failed the smog test, it’s illegal to drive it on public roads without proof that it’s been repaired (that’s why it has to be registered), so if you’re going to have repairs done in order to pass the smog test, make sure you budget in time for getting them fixed. You can find a list of approved repair technicians here.

When signing up for an appointment at a Smog Check station near you, remember that it will take about 30 minutes for an inspection unless there are any problems with your vehicle or delays at the testing center. If there are other people waiting ahead of you and everything goes smoothly with your inspection, expect about 20 minutes from start to finish.

Do you need to re-register a car that's had its exhaust system modified?

If you’ve changed your car’s exhaust system, you’ll need to re-register the vehicle. You can download a Vehicle/Vessel Transfer and Reassignment Form from the California Department of Motor Vehicles (DMV) website. Once you fill out the form, take it to your local DMV office and submit it along with any other appropriate fees. You’ll then be issued a new registration card for your vehicle that reflects the modifications made to its exhaust system.

If you’ve modified your exhaust system but don’t plan on re-registering the car in California, get ready to answer some hard questions when it comes time for your next smog test. An excessive amount of visible smoke emitted by a car may mean that its emissions control systems and filters are damaged or not working properly – which would cause the car to fail the smog test even if its tailpipe emissions were within legal limits.

California Smog Check Program (FAQ)

What is a smog check and why do I have to get one?

A smog check is an emissions test that inspects the amount of pollutants being emitted from your vehicle. California has had a smog program since 1984 in order to improve air quality and protect public health. Since motor vehicles are responsible for 80% of smog-forming pollutants in California, our Smog Check Program was designed to identify high polluting vehicles and require repairs so they can be brought into compliance with state emission standards.

How do car modifications affect smog tests?

You are required by law to keep your vehicle’s stock emission control systems fully operational. Any change, addition, or modification that alters the operation of any of these systems may be illegal and require a CAP exemption, or in some cases, a CAP waiver. Most aftermarket exhaust products will not pass visual inspection due to the removal of catalytic converters and addition of open pipes. Modifications that impact emissions are often not legal for use on emissions controlled vehicles used on public highways (including street legal ATVs).