Smog Check and Emissions Test Requirements: What States Require It and What to Expect

Whether you need a smog check depends on where you live, what you’re driving, and how old the vehicle is. Some states require emissions testing before every registration renewal. Others have no emissions program at all. And within states that do require testing, exempt vehicles — based on age, fuel type, or county — are common.

Getting this wrong means showing up at the DMV without a passing certificate, which means a second trip. This guide covers which states require emissions testing, what the test involves, what it costs, and how to handle a failure. This is part of the Used Car Buying Guide.

What a Smog Check Tests

A smog check (also called an emissions test or I/M test — inspection and maintenance) measures the pollutants a vehicle emits from its exhaust. The test is designed to identify vehicles that are burning fuel inefficiently or have malfunctioning emissions control systems.

The two main testing methods:

OBD-II scan (On-Board Diagnostics): For vehicles 1996 and newer, a technician plugs into the vehicle’s OBD-II port (under the dashboard, driver’s side) and reads the vehicle’s own self-diagnostic data. The test checks whether the vehicle’s emissions monitors have run and whether any trouble codes are present. This is the primary test method for modern vehicles.

Tailpipe test: For older vehicles without OBD-II systems (generally pre-1996), a probe is inserted into the tailpipe to directly measure exhaust emissions including hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx).

Visual inspection: In some states, technicians also visually check for obvious emissions equipment modifications — removal of the catalytic converter, for example, is a common cause of failure regardless of what the OBD scan shows.

EVAP test: California and some other states test the evaporative emissions system, which controls fuel vapor from the gas tank.

Which States Require Emissions Testing?

Emissions requirements vary widely. At a broad level:

States with statewide emissions programs: California, Connecticut, Delaware, Georgia, Illinois, Indiana, Maryland, Massachusetts, Missouri, Nevada, New Hampshire, New Jersey, New Mexico, New York, Ohio, Oregon, Pennsylvania, Rhode Island, Texas, Utah, Vermont, Virginia, Washington, Wisconsin

States with county-based requirements (testing only in certain counties): Arizona (Phoenix and Tucson areas), Colorado (Denver metro), Idaho (Ada County), Minnesota (Twin Cities metro), Tennessee (Shelby and Davidson counties)

States with no emissions requirements: Alaska, Alabama, Arkansas, Florida, Hawaii, Iowa, Kansas, Kentucky, Louisiana, Maine, Michigan, Minnesota (outside metro), Mississippi, Montana, Nebraska, North Carolina, North Dakota, Oklahoma, South Carolina, South Dakota, West Virginia, Wyoming

Note: This is approximate — states modify their programs regularly. Check with your specific state DMV for current requirements, especially if you’ve recently moved.

Common Exemptions

Even within states that require emissions testing, many vehicles are exempt:

By vehicle age: Most states exempt older vehicles from testing. California exempts vehicles 1975 and older. Many states exempt vehicles 25 years or older. Some states use a “rolling exemption” where the oldest year class is exempted each year.

By model year (new vehicles): Many states exempt new vehicles for the first 2–5 years of ownership, since new vehicles reliably meet emissions standards.

By fuel type: Electric vehicles are universally exempt. Diesel vehicles are subject to separate opacity tests in some states. Plug-in hybrids may be exempt in some jurisdictions.

By vehicle type: Motorcycles, golf carts, off-road vehicles, and heavy trucks are often handled under different programs or exempt entirely.

By mileage: Some states exempt low-mileage vehicles.

Check your state DMV’s exemption list — it’s common for buyers to discover their vehicle qualifies for an exemption they didn’t know existed.

How Much Does a Smog Check Cost?

Costs vary by state and station type:

• Basic OBD-II smog check: $30–$60 in most states
• California: $40–$80 for a standard test, $50–$90 for a STAR station test (required for vehicles with recent failures or high-mileage vehicles in enhanced areas)
• Texas: Around $25–$40
• New York: Included as part of the combined safety/emissions inspection, approximately $21 for the state fee
• Tailpipe test (older vehicles): $40–$80

Some states cap prices by statute. California, for example, regulates what smog stations can charge for the basic test.

When a Smog Check Is Required

At registration: Most states that require emissions testing require a passing certificate at each registration renewal (annually or every two years). New residents registering an out-of-state vehicle typically need a passing test before registration.

At sale: California requires a smog check within 90 days before a vehicle is sold, with the seller responsible for providing a passing certificate to the buyer. Many other states require testing at the time of title transfer when the buyer is registering in a test-required county.

After a failed test: If a vehicle fails, it must be repaired and retested before registration can proceed.

What Causes a Smog Test Failure

The most common reasons vehicles fail emissions tests:

Check engine light on: In an OBD-II test, an active check engine light (diagnostic trouble code) will cause an automatic failure in most states. The specific code often identifies the problem — a failing oxygen sensor, catalytic converter issue, or evaporative emissions leak are common culprits.

OBD monitors not ready: After a battery disconnect, reset, or recent repair, the vehicle’s emissions monitors may not have completed their self-checks. Running the vehicle through a specific drive cycle (a series of driving conditions) allows the monitors to complete. A vehicle with incomplete monitors fails the OBD test even without any active codes.

Catalytic converter failure: The catalytic converter reduces NOx, HC, and CO in exhaust. A failing or removed converter causes elevated emissions and automatic failure. Catalytic converter theft has become a significant issue — check the VIN history on any used vehicle to see if prior owners reported theft or damage.

EVAP system leak: Small leaks in the fuel vapor management system commonly cause failures in states that test the EVAP system.

What to Do If You Fail

Get the repair estimate: The technician should be able to tell you what codes are present and what repairs are likely needed. Get a written estimate.

Look for repair assistance programs: California (CAP — Consumer Assistance Program), Colorado, and several other states offer repair assistance grants of $500–$1,200 for qualifying low-income vehicle owners who fail emissions and need costly repairs.

Voluntary retirement programs: If repair costs exceed the vehicle’s value, some states offer cash payments to retire high-emitting vehicles. California’s vehicle retirement program pays $1,000–$1,500. Check your state’s DMV for equivalent programs.

Retest after repair: After repairs, the vehicle must be retested and pass before registration proceeds. In some states, you get a free retest within 30 days if the failure was at an official testing station.

Smog Check vs. Safety Inspection

These are two different things, though they’re sometimes combined:

A smog/emissions test checks what comes out of the exhaust — pollutants. It says nothing about whether the vehicle is mechanically safe.

A safety inspection checks whether vehicle systems — brakes, lights, tires, steering — meet safety standards. See state safety inspection requirements for details on which states require these.

Some states (New York, New Jersey, Virginia, and others) combine both into a single annual inspection. Others require only one or neither.

Buying a Used Car in a Smog-Required State

If you’re buying a used car in a state (or from a seller in a state) with emissions requirements, confirm who is responsible for the test:

Private party: In many states, the buyer is responsible for passing emissions as part of registration. In California, the seller must provide a passing test.

Dealer: Dealers in most states handle emissions testing as part of the sale process. Confirm this explicitly — don’t assume.

For any used vehicle purchase, run a Bumper VIN check to check for prior check engine light history, odometer issues, and any title concerns before committing to a purchase. A vehicle with a history of deferred maintenance is more likely to have emissions-related problems that weren’t disclosed.

Frequently Asked Questions

What states require a smog check? Roughly half of U.S. states have statewide or county-level emissions programs. States with statewide requirements include California, Texas, New York, New Jersey, Virginia, Massachusetts, Maryland, Connecticut, and others. States with no emissions requirements include Florida, Michigan, Ohio, Georgia, and most of the South and Great Plains. Many states that do require testing also have exemptions for new vehicles, old vehicles (pre-1976 in many states), and electric vehicles.

How much does a smog check cost? A basic OBD-II test runs $30–$60 in most states. California ranges from $40–$90 depending on the station type. Texas runs approximately $25–$40. New York bundles it with the safety inspection for around $21 in state fees. Some states cap prices by statute; others leave pricing to the market.

What causes a car to fail a smog test? The most common causes: an illuminated check engine light (active diagnostic trouble codes cause automatic failure in most states), OBD monitors that haven’t completed their self-checks after a recent battery disconnect or reset, a failed or missing catalytic converter, and EVAP system leaks in states that test evaporative emissions.

What do I do if my car fails a smog check? Get a written list of the specific failure codes from the technician, then have the necessary repairs completed. Return to an authorized station for reinspection — many states offer a free retest within 30 days at the same station. If repair costs are high, check whether your state has a repair assistance grant program (California’s CAP program offers up to $1,200 for qualifying low-income owners) or a vehicle retirement buyback program.

Do electric vehicles need a smog check? No — EVs produce no tailpipe emissions and are universally exempt from emissions testing. They may still be subject to safety inspections in states that require them.

How do I know if my car needs a smog check? Check your state DMV’s website for your vehicle’s registration requirements. Your renewal notice will typically indicate if a smog check is required. If you’ve just moved to a new state, check the new state’s requirements — your vehicle may need to pass a local emissions test before it can be registered.

How long is a smog check certificate valid? Typically 90 days to 2 years depending on state. California’s certificate is valid for 90 days. Most other states tie it to the registration period (annual or biennial).

Can I sell a car that failed a smog check? In most states, yes — the buyer assumes responsibility for passing emissions. In California, the seller must provide a passing test certificate.

What if my car just had its battery replaced and won’t pass OBD? Drive the vehicle through a normal driving cycle (highway and city driving) for 50–100 miles before retesting. This allows the OBD monitors to complete their self-checks. Your technician can advise on which monitors are incomplete.

Does a VIN check show emissions test history? Bumper VIN reports include available service and inspection records, including emissions test data in states that report it. Run a VIN check to see what’s available for a specific vehicle.

Run a Bumper VIN Check — See Inspection History and Check Engine Records →

Part of Used Car Buying Guide — The Used Car Buyer’s Ally

*Requirements are generalized. Check with your state for specific requirements.