Gasoline-powered vehicles within the Metro Denver and Front Range region of Colorado must be inspected for emissions. This area includes all or portions of Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, Jefferson, Larimer, and Weld counties.
The inspection frequency is based on the vehicle model year. Model year 1982 and newer vehicles are required to be inspected biennially (every two years), while 1981 and older model year vehicles are required to be inspected annually. The inspection cycle for new vehicles begins after a seven-model year exemption period. The exemption allows the newest and cleanest model year vehicles to forgo emissions inspections. Vehicles sold during their exemption period are also exempt from inspection as long as there are at least 12 months remaining in the exemption period.
To improve vehicle owner convenience, the AIR Program includes a Clean Screen program that uses remote sensing devices. The Clean Screen program monitors vehicle emissions while simultaneously photographing the license plate as a vehicle passes through infrared and ultraviolet beams of light. If the vehicle meets the program criteria, the vehicle owner is notified by the county clerk via a registration renewal card that is mailed to the address associated with the vehicle registration. These vehicles are not required to be inspected at an inspection station to complete the vehicle registration process.
Vehicles are exempt from inspection for the seven most recent model years.
Every vehicle built for sale in the United States since model year 1996 has an On Board Diagnostics (OBD) system. This feature helps find potential problems with the vehicle, leading to quicker repairs, improved performance, and better air quality.
The OBD inspection involves a visual assessment of the Malfunction Indicator Lamp (MIL) and an electronic query of the computer control system to determine if there are emissions problems. A vehicle’s OBD system commands the MIL on if the emissions output is elevated at least 1.5 times the Environmental Protection Agency certification levels.
A vehicle fails the OBD inspection if the MIL is illuminated or not functioning (visual fail) or the MIL is commanded on by the OBD system. A vehicle also fails the inspection process if a properly-functioning MIL is not commanded on when the vehicle is emitting visual opacity (smoke) or has a faulty or missing gas cap.
The OBD inspection also includes a functional inspection of the gas cap and a visual inspection of the exhaust for opacity (smoke).
The I/M240 inspection program uses a 240-second loaded-mode transient dynamometer inspection cycle to measure exhaust emissions. This emissions inspection cycle is a derivative of the Federal Test Procedure that is used to certify new vehicles for emissions.
The I/M240 inspection also includes a visual and pressure test of the gas cap and a visual inspection of the exhaust for opacity (smoke).
The Two Speed Idle (TSI) inspection measures vehicle emissions at idle and raised (2500 rpm) idle. Hydrocarbon (HC) and carbon monoxide (CO) emissions are measured with no engine load placed on the vehicle. Nitrogen oxides (NOx) emissions are not measured as part of the TSI inspection because NOx is not produced in significant amounts at idle and when the vehicle is not under load.
Instead of measuring the actual mass of emissions, TSI inspections measure the HC exhaust pollutant concentration levels in parts per million and by percent for CO.
The TSI inspection also includes a visual and pressure test of the gas cap and a visual inspection of the exhaust for opacity (smoke).