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Diesel Emissions Control Program

The State of Colorado controls diesel exhaust smoke by means of two diesel inspection and maintenance programs – one for fleets of nine (9) or more heavy-duty vehicles, and another for smaller fleets and privately-owned vehicles. 



Large Fleets


Owners and operators of larger diesel fleets take part in a Diesel Fleet Self-Certification Program. The program requires fleet owners and operators to self-inspect and certify their vehicles annually to maintain compliance with state smoke opacity standards. Fleets subject to the self-inspection and certification are those within the Automobile Inspection and Readjustment Program area with nine or more diesel vehicles of more than 14,000 pounds empty weight. New heavy duty diesel vehicles are exempt from testing for four (4) years.


Diesel Fleet Self-Certification

Large diesel fleets can click here to self-certify their emissions compliance.


Colorado Clean Diesel Program

The Colorado Clean Diesel Program provides no-cost diesel emission controls for school districts throughout Colorado. 



Small Fleets and Individuals


Small fleets and privately-owned diesel vehicles take part in the Diesel Opacity Inspection Program. This program is for all light-duty diesel vehicles as well as heavy-duty diesel vehicles not subject to the large fleet self-certification program. The Diesel Opacity Inspection Program requires that eligible vehicles be inspected on an annual basis by private, state-licensed diesel inspection stations.


New light-duty diesel vehicles are exempt from testing for four (4) years. The program applies only to the Automobile Inspection and Readjustment Program area and utilizes a loaded mode dynamometer-based test.