What Denver's Emission Test Requires
Denver requires an emission test every two years for most vehicles, and the test itself takes about 10 to 15 minutes. A technician will connect your car to a dynamometer — a machine that measures what comes out of your tailpipe while your engine runs under load. The test checks for nitrogen oxides, particulate matter, and hydrocarbons. Your vehicle either passes or fails; there is no partial credit.
The test applies to any vehicle registered in Denver County or the surrounding metro area counties (Adams, Arapahoe, Boulder, Douglas, El Paso, Jefferson, Larimer, and Weld). Vehicles older than 1975 and some electric or hybrid models are exempt. If your car fails, you have 60 days to fix the problem and retest at no additional charge.
Key Takeaways
- Denver emission tests happen every two years and cost between $20 and $30 depending on your vehicle type.
- You can test at any Colorado Department of Public Health and Environment (CDPHE) certified station, not just one location.
- A failing test does not prevent you from renewing your registration, but you must retest within 60 days or face a fine.
- Vehicles from 1975 and earlier, plus most electric and plug-in hybrid models, do not need to test.
Finding a Testing Station and What to Bring
The Colorado Department of Public Health and Environment maintains a searchable list of certified testing stations on their website. You can filter by county and city. Most stations are independent repair shops, not dealerships, and many are open evenings and Saturdays. Call ahead to confirm hours and whether you need an appointment — some take walk-ins, others require you to book a slot.
Bring your vehicle registration and proof of insurance. The technician will look up your vehicle's history in the state system, so they need your license plate number. If your check engine light is on, the station may refuse to test you until you address the underlying problem, because the light itself is a fail condition.
When Your Test Is Due and Renewal Timing
Your test is due in the month shown on your registration card — usually two years from the month you last registered. You can test up to 60 days before that month without penalty. If you test early, your new two-year window starts from the month you tested, not from when your old registration expired.
You do not have to test before you renew your registration online or by mail. However, the Colorado Division of Motor Vehicles will not issue your new registration sticker until a passing test result appears in the state system. If you renew first and then test, there is a gap where your registration is current but your test is not yet recorded — this is legal, but it means the DMV may flag your account if an officer runs your plate.
What Happens If Your Vehicle Fails
A failure notice will tell you which emissions standard your car exceeded. Common reasons include a faulty oxygen sensor, a clogged catalytic converter, or a malfunctioning fuel injector. The notice does not diagnose the problem — it only tells you what failed. You will need a mechanic to identify the cause.
You have 60 days from the test date to fix the vehicle and retest at the same station or a different one. The retest is free. If you do not retest within 60 days, the state will not renew your registration, and you cannot legally drive the vehicle. If you sell the car before retesting, the new owner inherits the failed test and the 60-day window.
Cost and Payment Methods
A standard emission test costs between $20 and $30. Diesel vehicles and vehicles over 14,000 pounds cost slightly more — usually $35 to $40. Most stations accept cash, card, and checks. Some offer discounts if you bring proof of low income, though this varies by station.
If you fail and need to retest, the retest is free at any certified station. You do not have to return to the same place you failed. Some repair shops bundle the test with diagnostic work, so if you use them to fix the problem, they may waive or reduce the retest fee.
Vehicles Exempt from Testing
Cars manufactured before 1975 do not test. Most electric vehicles (EVs) and plug-in hybrids (PHEVs) are exempt because they produce zero tailpipe emissions. However, a hybrid that is not plug-in capable — one that cannot run on battery alone — must still test. If you are unsure whether your vehicle qualifies, call a testing station with your vehicle identification number (VIN) and they can tell you in one minute.
Vehicles registered outside the Denver metro area counties do not need to test, even if you drive them in Denver regularly. The requirement is based on where the vehicle is registered, not where it is driven.
Frequently Asked Questions
Can I test before my registration expires?
Yes. You can test up to 60 days early. Your new two-year window will start from the month you tested, so testing early actually moves your next test date forward by a few months.
What if I move out of the Denver area after I register?
You are still required to test if your vehicle is registered in a Denver metro county. If you move to a county outside the testing area, you can transfer your registration to that county and stop testing. Contact the DMV about re-registering in your new county.
Do I need to test if I have a new car?
New cars are exempt from testing for the first four model years. After that, you test every two years like any other vehicle. Your registration paperwork will tell you when your first test is due.
What if the testing station says my car cannot be tested?
Some stations refuse to test vehicles with check engine lights on, or cars that are too damaged to safely connect to the dynamometer. If this happens, get the refusal in writing and contact the Colorado Department of Public Health and Environment. They can direct you to another station or explain your options.
Can I test in a different county than where I am registered?
Yes. Any certified station in Colorado can test your vehicle, regardless of which county issued your registration. The test result goes into the state system and counts toward your Denver area requirement.