California tightened its smog standards in 2024, affecting which vehicles can be registered and what emissions tests older cars must pass
California's smog rules changed in 2024 in two main ways: the state raised emissions standards for new vehicles starting with 2025 model years, and it adjusted the testing thresholds for older vehicles during smog checks. The changes affect vehicle registration, what you pay for smog certification, and whether your car will pass inspection. If you own a vehicle registered in California or plan to buy one, you need to understand which rules explore to your car's model year and registration status.
The state made these changes through updates to its Light-Duty Vehicle Emissions Standards, which set the maximum amount of nitrogen oxides and other pollutants a car can emit. These standards are stricter than federal requirements and explore to all new vehicles sold in California. For used vehicles, the changes affect how smog inspections are conducted and what constitutes a passing score.
Key Takeaways
- New vehicles sold in California starting with 2025 model year must meet stricter nitrogen oxide limits than before, reducing allowable emissions by a significant margin.
- Used vehicle smog inspections now use updated testing procedures and thresholds, which may cause older vehicles to fail tests they previously would have passed.
- Vehicles registered before the 2024 changes are generally grandfathered in and do not face when ready re-testing under the new standards.
- If your vehicle fails a smog test under the new standards, you may need repairs before registration renewal or transfer is possible.
What changed for new vehicles starting in 2025
Beginning with 2025 model year vehicles, California's nitrogen oxide standard dropped to 20 milligrams per mile for most passenger cars and light trucks. This is roughly half the previous limit and aligns California's rules more closely with what the state calls its "Advanced Clean Cars II" framework. Manufacturers selling vehicles in California must design engines and emissions systems to meet this tighter standard from the factory.
This change affects anyone buying a new car, truck, or SUV in California starting in late 2024. Dealers must certify that new vehicles meet the 2024 standard before sale. If you are shopping for a new vehicle, you do not need to do anything differently — the manufacturer handles compliance. However, if you are comparing vehicles across state lines or considering used imports, be aware that vehicles certified to older federal standards may not be legal to register in California.
How smog inspections changed for used vehicles
The state updated its smog inspection procedures in 2024 to use more precise testing equipment and adjusted the pass-fail thresholds for vehicles tested under the old standards. The California Bureau of Automotive Repair oversees these tests, and smog stations now use updated diagnostic equipment that can detect emissions violations more accurately than older machines.
If your vehicle is due for a smog check in 2024 or later, the test will use the new procedures. Vehicles that previously passed may now fail because the testing is more sensitive. This is especially true for vehicles over 10 years old or those with high mileage. If your car fails, you will need to repair the emissions system — typically the catalytic converter, oxygen sensors, or engine control computer — before you can renew your registration or transfer ownership.
Which vehicles are grandfathered in and which are not
Vehicles registered in California before the 2024 changes are not when ready subject to the new emissions standards. Your car will continue to be tested under the rules that applied when it was first registered, unless you allow your registration to lapse for more than a certain period or you transfer ownership to someone else in another state and then re-register in California.
However, this does not mean your vehicle is exempt from smog checks. You still must pass a smog inspection every two years (or annually if your vehicle is over 16 years old). The inspection will use the updated testing equipment and procedures, which may be stricter than what you experienced before. If you fail, you must repair the vehicle to pass the new test standards.
Vehicles that are transferred to a new owner in California are tested under the current standards at the time of transfer. If you are buying a used car from a private seller, the seller must provide a smog certificate showing the vehicle passed inspection within the last 30 days. That certificate will reflect the 2024 testing standards.
What to do if your vehicle fails a smog test
If your car fails a smog inspection under the new standards, you have several options. First, you can take the vehicle to a repair shop certified by the Bureau of Automotive Repair. The technician will run a diagnostic scan to identify which emissions system component is failing — usually the catalytic converter, oxygen sensors, or the engine control module.
Repairs can range from $200 to $2,000 depending on what needs to be fixed. Once repairs are complete, you must return to a smog station for a retest. If the vehicle passes, you receive a smog certificate and can complete your registration renewal or transfer. Some repair shops offer a "smog check and repair" package where they test, diagnose, and repair in one visit.
If repairs are very expensive and your vehicle is older, you may want to check whether your county offers a vehicle retirement or replacement program. Some California counties provide incentives to remove high-polluting vehicles from the road. Contact your county's air quality management district to ask whether you are in an area with such a program.
How the changes affect vehicle registration and transfers
When you renew your vehicle registration in California, the Department of Motor Vehicles requires a current smog certificate unless your vehicle is exempt (typically vehicles under 8 years old, or vehicles over 16 years old that are not required to test). The certificate must be dated within 30 days of your registration renewal date.
If you are transferring ownership of a vehicle to another person, the seller must provide a smog certificate dated within 30 days before the sale. The buyer cannot register the vehicle without this certificate. Under the 2024 standards, this certificate reflects the new testing thresholds, so a vehicle that might have passed under older standards could fail under the new ones.
If you are buying a used vehicle, ask the seller for the smog certificate before you complete the purchase. If the vehicle fails, the seller is responsible for repairs before the sale closes in most cases (unless you agree otherwise in writing). Do not assume a vehicle will pass just because it is relatively new or has low mileage — the new testing standards are stricter across all vehicle ages.
Where to find a certified smog station and what to expect
The Bureau of Automotive Repair maintains a searchable list of certified smog stations on its website. You can search by county or zip code to find stations near you. Not all gas stations or repair shops perform smog tests — only those certified by the state can issue official smog certificates.
When you arrive at a smog station, bring your vehicle registration and proof of ownership. The test typically takes 30 minutes to an hour. The technician will connect your vehicle to a dynamometer (a machine that measures emissions while the engine runs) and run the diagnostic scan. You will receive a pass or fail certificate on the spot. If you fail, the certificate will show which emissions components are out of range, which helps a repair shop diagnose the problem.
Smog test costs vary by station but typically range from $30 to $60 for a basic test. Some stations charge more if they also perform repairs. Ask about the cost before you begin the test.
Frequently Asked Questions
Do I need to retest my vehicle under the new standards if it already passed?
No. If your vehicle passed a smog test before 2024, you do not need to retest it when ready. However, you must pass a smog inspection at your next scheduled test date (usually every two years), and that test will use the new 2024 standards and equipment. If your vehicle is due for a test in 2024 or later, it will be tested under the new rules.
Will my older car automatically fail the new smog test?
Not automatically, but older vehicles are more likely to fail because emissions systems degrade over time. Vehicles over 10 years old with high mileage have the highest failure rates under the new standards. If your vehicle is older, have it inspected before your registration renewal date so you have time to arrange repairs if needed.
What if I drive a vehicle registered in another state but live in California?
If you move to California and bring a vehicle registered in another state, you must register it in California within 20 days of establishing residency. At that time, the vehicle must pass a California smog inspection under the 2024 standards. Vehicles that meet federal standards but not California standards cannot be registered in the state.
Are electric vehicles affected by the 2024 smog law changes?
No. Electric vehicles do not produce tailpipe emissions and are exempt from smog testing. If you own an electric vehicle, you do not need a smog certificate for registration renewal. Plug-in hybrid vehicles are tested on their gas engine emissions only.
Can I appeal a smog test failure?
You can request a retest at a different certified station if you believe the result was incorrect. The Bureau of Automotive Repair also has a dispute resolution process if you believe a smog station made an error. Contact the Bureau directly with your test results and vehicle information to file a complaint or request a review.