Buying or Selling a Car: Do You Need a Smog Check?
Learn when a smog check is required to buy or sell a car. Covers private sales, dealers, title transfers, out-of-state vehicles, and what to do if the car fails.
Read guideGuides
Emissions Testing & Smog Check Guides
Learn everything you need to know about emissions tests and smog checks. These step-by-step guides cover preparation, costs, state requirements, what happens during the test, common failure reasons, and how to pass your inspection on the first try.
How to pass your emissions test
A complete walkthrough of what to expect and how to prepare for your smog check.
Read guideWhat Is an Emissions Test and Why Does It Exist?
Learn what an emissions test is, why it exists, and what inspectors actually check. Plain-English guide to smog checks and vehicle inspections for drivers.
Read guideHow to Prepare Your Vehicle for an Emissions Test
Learn how to prepare your vehicle for an emissions test or smog check. Follow this checklist to avoid common failures and pass on your first visit.
Read guideOBD-II Emissions Testing: Check Engine Lights and Readiness Monitors
Understand how OBD-II emissions testing works, why a check engine light fails you, and how readiness monitors determine if your car is ready to test.
Read guideWhere to Get an Emissions Test or Smog Check Near You
Find out where to get an emissions test or smog check. Learn about station types, what to bring, how to verify authorization, and tips for avoiding long wait times.
Read guideHow Long Does an Emissions Test or Smog Check Take?
Find out how long an emissions test takes, what affects wait times, and how long your smog check results stay valid. Plan your visit and avoid deadline stress.
Read guideHow Much Does an Emissions Test or Smog Check Cost?
Find out how much an emissions test or smog check costs in your state. Learn what affects pricing, when tests are free, and how to avoid surprise fees.
Read guideHow Often Do You Need an Emissions Test?
Learn how often emissions tests are required in your state. Understand annual vs biennial testing, model year exemptions, and how to check your exact schedule.
Read guideWhat Happens If Your Vehicle Fails an Emissions Test?
Find out what happens after failing an emissions test. Learn about retests, repair requirements, waivers, and how failure affects your vehicle registration.
Read guideEmissions Testing and Vehicle Registration: Deadlines and Penalties
Learn how emissions testing affects vehicle registration. Understand deadlines, late fees, what happens if you fail, and how to get back into compliance.
Read guideLow-Income Assistance and Waivers for Emissions Repairs
Learn about emissions repair assistance programs, hardship waivers, and low-income help for smog check repairs. Find out if you qualify and how to apply.
Read guideEmissions Test Exemptions: Which Vehicles Do Not Need Testing?
Learn which vehicles are exempt from emissions testing. Covers electric vehicles, hybrids, new cars, classic vehicles, and heavy-duty trucks by state.
Read guideDiesel Emissions Testing for Light-Duty and Heavy-Duty Vehicles
Learn how diesel emissions testing works for cars, pickups, and heavy trucks. Covers OBD-II, opacity tests, state rules, and tips to pass your diesel smog check.
Read guideMoving to a New State: Emissions Test Requirements Checklist
Learn what emissions tests you need when moving to a new state. Covers new resident rules, whether your old test counts, grace periods, and a relocation checklist.
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About Our Emissions Testing and Smog Check Guides
Emissions testing rules are different in every state. Some states test every year, some every two years, and some only test in certain counties. The type of test your vehicle gets depends on its model year, fuel type, weight, and where it is registered. Our guides break all of this down so you know exactly what applies to your vehicle before you show up at the station.
What These Guides Cover
Each guide focuses on a specific part of the emissions testing process, from preparation to what happens after you get your results.
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How emissions tests and smog checks work, including OBD-II diagnostic scans, tailpipe measurements, and visual inspections of catalytic converters, gas caps, and exhaust systems.
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How to prepare your vehicle so you pass on the first visit, including warm-up procedures, readiness monitor checks, and what to do about a check engine light.
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What an emissions test costs in every state, from free programs in Ohio and Wisconsin to market-rate smog checks in California and Nevada.
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Common reasons vehicles fail, including catalytic converter problems, oxygen sensor faults, EVAP leaks, and incomplete readiness monitors.
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Exemptions for new vehicles, classic cars, electric vehicles, hybrids, diesels, and low-mileage vehicles.
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What to do after a failed test, including repair options, retesting rules, repair cost waivers, and state assistance programs for low-income drivers.
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How emissions testing connects to vehicle registration, including deadlines, late fees, and what happens if you cannot pass before your registration expires.
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State-specific requirements for drivers who are moving, buying or selling a vehicle, or registering a car from out of state.
Updated for 2026
Emissions programs change regularly as states update their Clean Air Act compliance plans, adjust fees, expand or shrink testing areas, and modify exemption rules. Several states made significant changes heading into 2026, including New Hampshire suspending its inspection program, Colorado raising fees and adding self-service kiosks, Ohio increasing its repair waiver threshold, and North Carolina preparing to drop emissions testing in 18 counties.
All of our guides are reviewed and updated to reflect current 2026 requirements, procedures, and fee schedules. When a state changes its rules, we update the relevant guides and publish new content covering what changed and what drivers need to know.
Find Your State's Requirements
Our state directory pages cover every state with an active emissions testing program, including county-level details, station locations, current fees, exemption rules, and testing schedules.
If you want to know exactly what your vehicle needs in your area, start with your state page and use these guides to fill in the details.
Browse all statesFAQ
Common questions
Get clear answers about emissions testing guides, state requirements, smog check preparation, and what to do after a failed inspection.
Are these emissions testing guides specific to my state?
Are these emissions testing guides specific to my state?
Our guides cover the general process and rules that apply across most states, with specific callouts for states that do things differently. For state-specific details like which counties require testing, current fees, exemption model years, and station locations, use our state directory pages alongside the guides.
Can I use these guides to prepare for a California smog check?
Can I use these guides to prepare for a California smog check?
Yes. Our preparation guide, OBD-II guide, and failure guide all apply to California's Smog Check program. California uses OBD-II testing for most vehicles, requires STAR station visits for flagged vehicles, and offers repair assistance through the BAR Consumer Assistance Program. Our California state page covers the specifics.
Do these guides cover diesel emissions testing?
Do these guides cover diesel emissions testing?
Yes. We have a dedicated guide for diesel emissions testing that covers OBD-II diagnostics for newer diesels, opacity smoke testing for older models, DPF and EGR system requirements, and state-by-state rules for light-duty and heavy-duty diesel vehicles.
Will these guides help if my vehicle already failed?
Will these guides help if my vehicle already failed?
Yes. Our guide on what happens after a failed emissions test covers your retest options, repair priorities, how to qualify for a repair cost waiver if your state offers one, and how to apply for low-income repair assistance programs. We also have a separate guide on waivers and financial assistance.
How often are these guides updated?
How often are these guides updated?
We review and update guides whenever states change their emissions testing rules, fees, or exemptions. Major updates are published as standalone blog posts covering what changed and why it matters. The guides themselves are updated on an ongoing basis to stay current with 2026 requirements.
I am moving to a new state. Which guide should I read first?
I am moving to a new state. Which guide should I read first?
Start with our moving to a new state checklist. It covers new resident registration deadlines, whether your previous state's test counts, grace periods, and what to expect at your first inspection in the new state. Then check the state page for your new state to see the specific requirements for your area.
Can I suggest a new guide topic?
Can I suggest a new guide topic?
Yes. If there is a topic we have not covered or an area where you want more detail, contact us and we will consider adding it. Many of our guides started as questions from drivers who could not find clear answers anywhere else.
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