The Oklahoma Diesel Engine Freedom Act establishes the state's authority to regulate emissions standards for vehicles operating solely within its borders, asserting that federal mandates requiring the use of diesel exhaust fluid in diesel engines exceed the constitutional powers granted to Congress. The Act declares such federal regulations null and void and prohibits state agencies or officials from enforcing these mandates. It also allows for the manufacture, sale, and installation of diesel engines that do not require diesel exhaust fluid, exempting them from federal emissions standards as long as they are used exclusively within Oklahoma.

Additionally, the Act imposes penalties for any state agency, political subdivision, or individual found enforcing federal diesel exhaust fluid mandates, including civil fines of up to $5,000 per violation, suspension of enforcement authority for at least twelve months, and potential termination of employment for state officers. The bill also repeals a previous section of law related to emission control systems, specifically 47 O.S. 2021, Section 12-423. An emergency clause is included, allowing the Act to take effect immediately upon passage and approval.