Colorado Smog Laws: Requirements, Exemptions, and Penalties

Colorado’s smog laws require most gasoline and diesel vehicles registered in the Denver metro area and parts of the northern Front Range to pass an emissions test before their registration can be renewed. Testing costs $35 for 1982 and newer gasoline vehicles and $20 for older ones, happens every one or two years depending on the vehicle, and skipping it means you cannot renew your tags.¹

Who Has To Test

Emissions testing applies only inside the program area, not statewide. The current area covers Boulder, Broomfield, Denver, Douglas, and Jefferson counties in full, plus portions of Adams, Arapahoe, Larimer, and Weld counties.² Parts of El Paso County also require diesels to pass an opacity test before a sale.³ If your vehicle is registered outside these areas, you have no emissions obligation under this program.

Testing type depends on your vehicle. Most 1996 and newer gasoline cars get a quick on-board diagnostics check. Older gasoline vehicles get a dynamometer or idle test. Diesels get an opacity test, with a limit of 20% measured over five seconds.⁴ Air Care Colorado stations handle gasoline testing; private licensed stations handle diesel.

How Often and What It Costs

Your renewal postcard tells you when a test is due. The schedule breaks down by fuel and age:

Gasoline, 1982 and newer: every two years, after the seven-year new-vehicle exemption ends.⁵
Gasoline, 1981 and older: every year.⁵
Diesel, newer than 10 model years: every two years.
Diesel, 10 model years and older: every year.⁶

Fees at Air Care Colorado stations are $35 for gasoline vehicles from 1982 or newer and $20 for 1981 and older models.¹ A VIN verification, if you need one, is $25.⁷ Diesel opacity test fees vary by provider.

Vehicles That Are Exempt

Not every vehicle in the program area needs a test. The main exemptions:

New gasoline vehicles are exempt for their first seven model years. A 2026 model would not need testing until 2033. The exemption transfers to a new owner if at least 12 months remain on it.⁵
New diesel vehicles are exempt for their first four model years. Heavy-duty diesels under 26,000 pounds GVWR are also exempt for four years; those over 26,000 pounds get six years.³
All-electric vehicles are permanently exempt.⁴
Model year 2026 hybrids are currently exempt. Older hybrids follow the standard gasoline schedule.⁵
Collector vehicles from 1975 or older are permanently exempt when registered with collector plates. Collector vehicles from 1976 or newer are exempt only if registered as a collector’s item before September 1, 2009, with no lapse in registration or change of ownership since.⁵
Motorcycles, autocycles, kit cars, horseless carriages, street rods, and farm vehicles are permanently exempt.⁴

Skipping the Station With RapidScreen

Colorado runs a program called RapidScreen that can save you the trip entirely. Roadside sensing equipment measures your vehicle’s emissions as you drive past. If the reading is clean, you get credit for a passing test and can skip the station when it’s time to renew.⁸ Your renewal postcard will say if your vehicle qualified.⁵

You don’t sign up for it. The screening happens automatically in normal traffic. Whether you get screened depends on where you drive and when the equipment is active.

If Your Vehicle Fails

A failure means you need repairs and a retest. Before writing large checks, know that Colorado offers two waiver paths.

A repair waiver is available if you’ve spent a qualifying amount on emissions-related repairs in the past six months and the vehicle still won’t pass:

Gasoline vehicles, 1968 and newer: $715 in qualifying repairs
Gasoline vehicles, 1967 and older: $75
Light-duty diesel (14,000 lbs or less): $750
Heavy-duty diesel (over 14,000 lbs): $1,500⁹

The waiver lets you register for one inspection cycle without meeting standards. Cost limits and failed-test records reset annually, so you cannot bank prior spending toward a later waiver.⁹

A separate economic hardship waiver exists for owners who cannot afford the repairs. Either waiver will be denied if the vehicle produces visible smoke.⁹

Buying or Selling a Vehicle

Emissions rules create real obligations at the point of sale. In a private sale, the seller must give the buyer a passing emissions test that hasn’t already been used to register or renew the vehicle.⁴ Any change of ownership triggers a test requirement, even if the car isn’t yet due for its biennial cycle.⁵ If you’re buying, get the certificate before you pay.

Licensed dealers must provide either a passing test or a voucher good for one free test at the time of sale. Under the Deter Tampering Motor Vehicle Emissions Control System Act (SB 22-179), dealers are liable for the vehicle’s emissions compliance for five business days after purchase.⁴

There is one exception. If a vehicle is inoperable or cannot be tested, the seller may sell it without a passing test only by giving the buyer written notice that the vehicle does not comply, that the seller does not warrant that it will, and that the buyer is responsible for bringing it into compliance before registering it in the program area.¹⁰

What Happens If You Skip Testing

The first consequence is a registration hold. You cannot renew your tags without a passing test or an approved waiver. Driving on expired registration draws a late fee of $25 to $100 for each month past expiration.¹¹ Operating an unregistered vehicle is a class B traffic infraction with a fine of $15 to $100.¹²

Colorado also prohibits “nuisance exhibition of motor vehicle exhaust,” meaning deliberately blowing soot, smoke, or particulate emissions from a vehicle under 14,000 pounds GVWR in a way that obscures another person’s view or creates a hazard. This targets the practice known as rolling coal. A violation is a class A traffic infraction carrying a $100 fine with no points assessed on your license.¹³

Disputing a Test Result or Registration Denial

If you think your vehicle failed because of an equipment or testing error, you can get a retest at any certified Air Care Colorado station. Bring documentation of recent repairs.

If your registration transaction is denied in writing, you can request a formal hearing through the Department of Revenue Hearings Division within 60 days of the denial notice. Include your VIN and a copy of the denial letter with your request.¹⁴

Citations for expired registration or nuisance exhaust can be contested in municipal or county court. Maintenance records, repair receipts, and a recent passing emissions certificate are the strongest evidence you can bring.

1
AirCare Colorado. Need to Know
2
Colorado Department of Revenue – Motor Vehicle. Gas Vehicles
3
Colorado General Assembly. Emissions
4
Colorado Department of Revenue – Motor Vehicle. Emissions
5
Colorado Department of Revenue. Gas Emissions Requirements
6
Colorado Department of Public Health and Environment. Emissions Inspections for Diesel-Powered Vehicles
7
Air Care Colorado. Air Care Colorado Home Page
8
Colorado Department of Revenue – Motor Vehicle. What Is RapidScreen
9
Department of Revenue – Motor Vehicle. Emissions Waivers
10
Justia. Colorado Code 42-4-310 – Periodic Emissions Testing
11
Colorado General Assembly. SB22-123 Late Vehicle Titling and Registration Penalties
12
Justia. Colorado Code 42-3-103 – Registration Required – Exemptions – Rules
13
Justia. Colorado Code 42-4-314 – Tampering
14
Department of Revenue – Motor Vehicle. Vehicle Services Hearings