Colorado Smog Laws: Requirements, Exemptions, and Waivers

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 the state will renew their registration. Testing fees run $35 for 1982 and newer gasoline vehicles and $20 for older models, and skipping the process leads to a registration hold, monthly late fees, and a possible traffic infraction for driving on expired tags.

Who Has to Get Tested

Emissions testing applies only to vehicles registered in specific counties. The program area covers Boulder, Broomfield, Denver, Douglas, and Jefferson counties in full, plus portions of Adams, Arapahoe, Larimer, and Weld counties.¹ Parts of El Paso County also require diesel vehicles to pass an opacity test before a sale.² If your vehicle is registered anywhere else in Colorado, you have no emissions testing obligation.

Within the program area, your renewal postcard tells you whether a test is due this cycle.

How Often You Need a Test

Testing frequency depends on fuel type and age:

Gasoline, 1982 and newer: every two years, once past the seven-year new-vehicle exemption.³
Gasoline, 1981 and older: every year.³
Diesel, newer than 10 model years: every two years.
Diesel, 10 model years and older: every year.⁴

Gasoline vehicles are tested at Air Care Colorado stations or licensed independent test stations. Light-duty diesels and small fleets go to private, state-licensed diesel inspection stations, which measure smoke density against a 20% opacity standard over five seconds.⁵⁴

Vehicles That Are Exempt

Several categories of vehicles never need a test, or are exempt for a period after purchase.

New gasoline vehicles are exempt for the first seven model years. A 2026 model would not need testing until 2033. The exemption transfers to a buyer if at least 12 months remain on it.³
New diesel vehicles are exempt for the first four model years. Heavy-duty diesels under 26,000 pounds GVWR are also exempt for four years; those over 26,000 pounds are exempt for six.²
All-electric vehicles are permanently exempt.⁵
2026 model year hybrids are currently exempt. Older hybrids follow the standard gasoline schedule.³
Collector vehicles from 1975 and older are permanently exempt when registered with collector plates. Collector vehicles from 1976 and newer are exempt only if they were registered as collectors before September 1, 2009, with no lapse in registration or change of ownership since.¹³
Motorcycles, autocycles, kit cars, horseless carriages, street rods, and farm vehicles are all permanently exempt.⁵

What It Costs and How to Skip the Station

Air Care Colorado charges $35 for 1982 and newer gasoline vehicles and $20 for 1981 and older models.⁶ A VIN verification, if the state needs one, is $25.⁷ Diesel opacity fees vary by station.

You may not need to visit a station at all. Colorado runs a program called RapidScreen that uses roadside sensors to measure vehicle emissions in normal traffic. If your car reads clean when it passes a RapidScreen site, you get credit for a passing test, and your renewal postcard will say so.⁸³ Nothing to sign up for; it happens automatically if you drive past the right spot at the right time.

What Happens If Your Vehicle Fails

A failed test means you need repairs and a retest before you can register. Colorado has two waiver programs that can get you around a continuing failure, but both have the same hard limit: the DMV will deny a waiver if your vehicle produces visible smoke.

Repair Waiver

If you’ve spent a qualifying amount on emissions-related repairs in the past six months and your vehicle still won’t pass, you can apply for a repair waiver. The spending thresholds are:

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

A repair waiver lets you register for one inspection cycle without meeting standards. Cost limits and failed test records reset each year, so repair spending from a previous year won’t count toward a new application.⁹

Economic Hardship Waiver

A separate economic hardship waiver is available for owners who cannot afford the repairs. Same visible-smoke exclusion applies.⁹

Buying or Selling a Vehicle in the Program Area

A sale triggers testing even if the vehicle isn’t yet due for its regular biennial check.³ In a private sale, the seller must give the buyer a passing emissions test that hasn’t already been used for a registration or renewal.⁵ If you’re the buyer, get the certificate in hand 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 remain liable for the vehicle’s emissions compliance for five business days after the purchase date.⁵

One exception exists for vehicles that are inoperable or otherwise cannot be tested. The seller can transfer the vehicle without a passing test if they give the buyer a written notice stating 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

Penalties for Noncompliance

The first consequence of skipping an emissions test is a registration hold. You cannot renew without a passing test or an approved waiver, and driving on expired registration carries a late fee of $25 to $100 for each month past expiration.¹¹ Operating an unregistered vehicle is a class B traffic infraction, with fines from $15 to $100.¹²

Colorado separately prohibits what the statute calls “nuisance exhibition of motor vehicle exhaust,” meaning deliberately blowing soot, smoke, or particulate from a vehicle under 14,000 pounds GVWR in a way that obscures another person’s view or creates a hazard. The practice is commonly called “rolling coal.” A violation is a class A traffic infraction with a $100 fine and no points on your license.¹³

Disputing a Failed Test or a Registration Hold

If you believe a failed test was wrong, you can get a retest at any certified Air Care Colorado station. Bring documentation of recent repairs.

If the DMV refuses your registration, you can request a formal hearing within 60 days of the written denial through the Department of Revenue Hearings Division. Include your VIN and a copy of the denial letter.¹⁴

If you receive a traffic citation for expired registration or a nuisance exhaust violation and believe it was unjustified, you can contest it in municipal or county court. Maintenance records, repair receipts, and a recent passing emissions test are the strongest evidence to bring.

1
Colorado Department of Revenue – Motor Vehicle. Gas Vehicles
2
Colorado General Assembly. Emissions
3
Colorado Department of Revenue. Gas Emissions Requirements
4
Colorado Department of Public Health and Environment. Emissions Inspections for Diesel-Powered Vehicles
5
Colorado Department of Revenue – Motor Vehicle. Emissions
6
AirCare Colorado. Need to Know
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