What California's emissions laws require
California sets its own vehicle emissions standards instead of following the federal EPA rules that most other states use. The state's standards are stricter than federal ones, which is why you'll see "California emissions" listed as a separate category on vehicle spec sheets. If you own or drive a vehicle registered in California, your car must meet these standards, and you must pass an emissions test every two years (or annually for vehicles older than 1975).
The core requirement is straightforward: your vehicle's tailpipe emissions must stay below specific limits for nitrogen oxides, particulate matter, and other pollutants. Newer vehicles (generally 2000 and later) have onboard diagnostic systems that the test machine reads to check whether your emissions controls are working. Older vehicles are tested directly at the tailpipe. If your vehicle fails, you cannot renew your registration until you fix the problem and pass a retest.
Key Takeaways
- California emissions standards are stricter than federal EPA standards, and your vehicle must meet California's limits if it is registered in the state.
- Most vehicles must pass an emissions test every two years; vehicles older than 1975 test annually, and some newer vehicles may test every four years.
- The test checks either your onboard diagnostic system (for 2000 and newer vehicles) or your tailpipe emissions directly (for older vehicles).
- If you fail, you have 30 days to fix the vehicle and retest at no additional fee; if you cannot fix it, you may be able to transfer your registration to a different state or explore for a waiver.
Which vehicles must test in California
Nearly every vehicle registered in California must pass an emissions test, with a few exceptions. Diesel vehicles registered before 1998 are exempt. Vehicles registered in California but garaged outside the state for more than 12 months in a row can request an exemption. Electric vehicles and hydrogen fuel-cell vehicles do not test. Vehicles that are brand new (zero miles) and have never been registered anywhere are exempt for their first test cycle.
The test frequency depends on your vehicle's model year and type. Most gasoline vehicles test every two years. Vehicles older than 1975 test every year. Some newer vehicles (generally 2010 and later, depending on the model) may test every four years if they pass their first test and have no check-engine light. Diesel vehicles that do test (1998 and newer) follow their own schedule, which varies by model year.
If you are unsure whether your vehicle must test, the California Department of Motor Vehicles website has a lookup tool, or your smog check station can tell you when you arrive. Bring your registration or vehicle identification number (VIN).
How the test works and what happens if you fail
A smog check station will connect a diagnostic scanner to your vehicle's onboard computer (for 2000 and newer vehicles) or place a probe in your tailpipe (for older vehicles). The test takes about 10 to 15 minutes. For newer vehicles, the scanner reads whether your emissions control systems are functioning and whether any fault codes are stored. For older vehicles, the machine measures the actual pollutants coming out of the tailpipe and compares them to California's limits.
If you pass, the station prints a certificate and reports the result to the DMV electronically. Your registration renewal will go through. If you fail, the station gives you a detailed report showing which emissions are too high or which systems are not working. You then have 30 days to repair the vehicle and return to any smog check station for a retest at no additional charge. The retest is free even if you go to a different station.
If you cannot afford to repair the vehicle or the repair cost exceeds a certain threshold (currently $500 for most vehicles, though this varies), you may be able to request a waiver from the DMV. A waiver allows you to register the vehicle anyway, though you will still need to test again at your next renewal. Waivers are not may provide and depend on your vehicle's age and repair history.
Vehicles that fail repeatedly or cannot be fixed
If your vehicle fails the test two years in a row, or if the repair cost exceeds the waiver threshold and you cannot pay for it, you have limited options. You can request a Gross Polluter Abatement Program waiver, which allows you to register for one more year while you save for repairs. After that year, if the vehicle still fails, you may need to retire it or transfer your registration to another state.
Some California counties offer vehicle retirement or trade-in programs that provide cash or vouchers toward a newer vehicle if you agree to scrap your old one. These programs are run by local air quality management districts, not the state, so availability and incentive amounts vary by county. Your smog check station or local DMV office can tell you whether your county has a program.
If you move out of California permanently, you can transfer your registration to your new state and no longer test in California. However, if you keep a California registration, you must continue to test even if you live elsewhere.
What causes a vehicle to fail emissions testing
The most common reason for failure is a check-engine light caused by a faulty oxygen sensor, catalytic converter problem, or fuel system leak. These are usually fixable repairs that cost between $100 and $500. A failing catalytic converter is more expensive (often $500 to $1,500) but is the most common major repair needed.
Older vehicles (pre-2000) often fail because of worn engine components, a clogged air filter, or old spark plugs. These are usually cheaper to fix than catalytic converter issues. Diesel vehicles sometimes fail because of excessive soot in the particulate filter, which can sometimes be cleared by a professional cleaning or by driving the vehicle on the highway for an extended period.
A vehicle can also fail if the onboard diagnostic system detects that emissions tests have been tampered with or if the vehicle has been modified in a way that disables emissions controls. Removing or disabling a catalytic converter, for example, will cause an when ready failure and may result in fines beyond the cost of repair.
How California's standards differ from federal standards
California has a waiver from the federal Clean Air Act that allows it to set its own emissions standards. These standards are generally 50 to 70 percent stricter than federal EPA standards. For example, California's limit for nitrogen oxides is lower, and the state tests for additional pollutants that the federal test does not measure.
Because California's market is so large, many vehicle manufacturers build all their vehicles to California standards rather than making two versions. This means that even if you buy a vehicle outside California, it may already meet California standards. However, some older used vehicles from other states may not, and if you move to California with an out-of-state vehicle, you will need to have it tested and may need repairs to pass.
Other states have adopted California's standards instead of the federal ones. These are sometimes called "CARB states" (California Air Resources Board states). If you move from California to one of these states, your vehicle will likely still pass their tests. If you move to a federal EPA state, your vehicle will pass easily since California standards are stricter.
Preparing for your emissions test
Before you go to a smog check station, make sure your vehicle is in good running condition. Warm up the engine for at least 20 minutes before the test (a short drive is ideal). Make sure your gas cap is tight and not damaged, since a loose or missing cap can trigger a check-engine light. If your check-engine light is on, get it scanned at a repair shop before testing; the smog check station will not clear the code for you.
Bring your registration or proof of ownership and your vehicle identification number (VIN). Some stations accept appointments; others are first-come, first-served. The test costs between $30 and $70 depending on your vehicle type and location. If you fail and need a retest, the retest is free, but you will need to pay for any repairs yourself.
If your vehicle is very old or has a history of emissions problems, consider having a trusted mechanic inspect it before you test. A pre-test inspection costs $50 to $100 but can save you money if it identifies a cheap fix that will help you pass.
Frequently Asked Questions
Do I have to test every year or every two years?
Most vehicles test every two years. Vehicles older than 1975 test annually. Some newer vehicles (generally 2010 and later) may test every four years if they pass their first test and have no check-engine light. Your registration notice will tell you when your test is due.
What if I just moved to California with a vehicle registered in another state?
You must register your vehicle in California within 20 days of moving. Once registered, your vehicle will be subject to California emissions standards. You will need to pass an emissions test before or shortly after you register it, depending on your county. Some counties allow a grace period; others require the test before registration is complete.
Can I drive my vehicle if my emissions test is overdue?
No. If your registration has expired because your emissions test is overdue, driving the vehicle is illegal. You must pass the test and renew your registration before you drive. If you are pulled over, you can face a fine. Schedule your test as soon as your registration notice arrives.
What if my vehicle has been modified or has an aftermarket part?
Any modification that changes how your vehicle's emissions systems work will likely cause a test failure. This includes removing a catalytic converter, installing a non-approved air intake, or reprogramming the engine computer. These modifications are illegal in California and can result in fines. You must remove the modification and restore the vehicle to its original emissions-compliant state to pass the test.
Can I test in a different county than where my vehicle is registered?
Yes. You can test at any smog check station in California, regardless of which county your vehicle is registered in. However, you must still follow your county's test schedule. Some counties have stricter or more frequent testing requirements than others.