Diesel Emissions Requirements

Boulder County requires that diesel vehicles pass an emissions test in order to be registered. Details about requirements and exemptions are listed below as well as on the state’s Diesel Emissions Program page.

Diesel Emissions Requirements

Unless the vehicle is exempt (see below), the following requirements apply:

• Gross Vehicle Weight Rating (GVWR) up to 26,000 pounds require an emissions test starting in their fifth model year. In 2025, this means vehicles that are 2020 or older require a test.)
  • 9 years old and newer require an emissions test every two years.
  • 10 years old and older require an emissions test annually.
  • 1976-1989 with collector plates require a test every 5 years.
• Gross Vehicle Weight Rating (GVWR) 26,000 pounds or more require an emissions test starting in their seventh model year. In 2025, this means vehicles that are 2019 or older require a test.
  • 9 years old and newer require an emissions test every two years.
  • 10 years old and older require an emissions test annually.
  • 1976-1989 with collector plates require a test every 5 years.

Test Locations

Several testing locations are available for diesel vehicles. Diesel vehicles are not tested at Air Care Colorado.

Emissions Testing for Registration Renewal

Obtain an emissions test if the statement “Emissions Test is Required” appears on the vehicle registration renewal notice.

• Diesel emissions test results are typically posted electronically to registration records within 2-3 days.
  • If you’d like to renew earlier than 2-3 days after your test, you are welcome to drop off or mail in your passing emissions test with a check. We can also help you over the phone if you call 303-413-7710.
• Once your passing emissions test has been posted electronically, you can renew your registration online or at a MV Express kiosk.

Diesel Emissions Exemptions

The following diesel vehicles are exempt from emissions requirements:

• Gross Vehicle Weight Rating (GVWR) up to 26,000 pounds:
  • Vehicles within the first four model years (In 2023, this means vehicles that are 2020 or newer are exempt.)
    • Exception: If vehicle ownership is being transferred in the last year of the four-year exemption, an emissions test will be required. (In 2023, this means that a 2020 vehicle will require an emissions test if there is a transfer of ownership.)
  • Vehicles 1975 and older with collector plates
  • Vehicles 1976 or newer that have been grandfathered (i.e. registered as a “collector’s item” prior to September 1, 2009 and registration has never lapsed/expired/or had a change of ownership)
• Gross Vehicle Weight Rating (GVWR) 26,000 pounds or more:
  • Vehicles within the first six model years (In 2023, this means vehicles that are 2018 or newer are exempt.)
    • Exception: If vehicle ownership is being transferred in the last year of the six-year exemption, an emissions test will be required. (In 2023, this means that a 2018 vehicle will require an emissions test if there is a transfer of ownership.)
  • Vehicles 1975 and older with collector plates
  • Vehicles 1976 or newer that have been grandfathered (i.e. registered as a “collector’s item” prior to September 1, 2009 and registration has never lapsed/expired/or had a change of ownership)
• If an exempt vehicle tests for emissions anytime during the exemption period, the exemption period is invalid and the vehicle must be tested every two years.