Colorado Emissions

Colorado has an overall strategy that has been put in place in order to improve the air quality in and around major cities such as Denver, Boulder and the North Front Range. In order to administer this, vehicle emissions testing has been put in place.

Vehicles are responsible for much of the harmful air pollution that is in our air that can lead to negative health issues. The testing program has been designed to try to reduce these pollutants, especially ozone emissions.

Emissions Inspections

Residents of certain counties are required to have emissions inspections. However the type of test is required depends on both the year of your vehicle and the county in which you live in.

Every vehicle must also go through a VIN inspection. Although safety inspections are not required in the state of Colorado, an emissions inspector will often check to make sure that your vehicle does not contain any major safety issues that may be affecting the emissions tests. If your vehicle has been deemed unsafe to test, you will fail the test.

I/M Emissions Test

This test looks for dangerous gases such as carbon monoxide, hydrocarbons and nitrogen that are emitted from a vehicle for a period longer than four minutes. First, the inspector does a visual inspection of the emissions equipment. Next the vehicle is tested using a dynamometer, which allows for simulated driving conditions so that emissions can be measured from the tailpipe.

Then, a gas seal test is performed once the test has been completed. Finally, you will be provided with a report that shows how your vehicle performed and if it passed or failed.

Two speed idle test

Another test that will be completed looks for carbon monoxide and hydrocarbons to see if they are emitted from the vehicle. With this test a probe is inserted into the tailpipe and is used to measure pollutants as they are emitted. Your vehicle will run idle for 30 seconds as the readings are taken.

Then, the vehicle is sped up to 2500 rpm’s for 30 seconds as the readings are taken. Finally, it is slowed back down to idle speed for an additional 30 seconds while readings are taken again. You will also receive a report this test as well.

Diesel opacity test

If your vehicle runs on diesel, you will undergo this test. An opacity meter will be used to measure if air pollution obscures sight through exhaust smoke.

Dynamometer test

This test inspects all-wheel-drive and traction control vehicles in order to determine the amount of force or torque that the vehicle produces. During this test, the dynamometer will spin both front and rear wheels at the same time.


There are exemptions when it comes to emissions tests in Colorado, but if you lived in certain counties you will be required to have a test completed regardless. While some counties require testing throughout the entire county others only require it in certain parts. The state does offer maps so that you can determine if you live in the required area or not.