Emissions testing when you buy a used car in the Denver metro
Who has to test, who pays, what the certificate is, and the five-business-day rule that protects you when you buy from a dealer.
Updated October 12, 2026 · 2 min read
If you register a car in the Denver metro area, you will deal with emissions testing. This is the short version for buyers.
Who has to test
The emissions program covers the Denver-Boulder metro counties, including Arapahoe County, where Aurora sits, and the urban parts of Larimer and Weld to the north. The rules that matter when you buy:
- Newer gasoline cars are exempt for their first seven model years. A 2021 model bought in 2026 does not need a test yet.
- Fully electric cars are exempt. Hybrids are not; they test like any gasoline car.
- Older gasoline and diesel cars need a passing test to be registered, and then again every two years.
Who provides the certificate
When you buy from a licensed Colorado dealer, the dealer has to furnish a passing Certificate of Emissions Compliance (or a voucher for the test) with the car, if the car needs one. You should not be sent to the test station to find out whether the car passes.
Colorado tightened this in 2022 (Senate Bill 22-179): the dealer remains responsible for emissions for five business days after the sale. If the car fails in that window, the repair is on the dealer, not on you.
What the test costs and where
Tests happen at Air Care Colorado stations. The fee for a standard gasoline test is about $25. There are drive-through stations around the metro, and most older cars are also screened by roadside sensors; if your car is clean enough to pass that way, you get a letter and skip the station.
What a passed test does not tell you
A passing emissions test means the car’s emissions system was working on the day of the test. It is not a mechanical inspection and says nothing about the transmission, brakes, tires, or the battery of a hybrid. Treat it as one box checked, not a bill of health.
What we do
Every car on our lot that needs a certificate has one before it is listed, and the listing says so. You get the certificate with the paperwork, and the five-day protection applies to every sale, the way the law requires.