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 these vehicles are unconstitutional. The Act nullifies any federal regulation or executive order related to this requirement, emphasizing the state's right under the 10th Amendment to the U.S. Constitution. It prohibits state agencies and officials from enforcing such federal mandates and allows for the manufacture, sale, and installation of diesel engines that do not require diesel exhaust fluid, declaring them exempt from federal emissions standards as long as they are used exclusively within Oklahoma.

Additionally, the Act sets forth civil fines for any state agency, political subdivision, or individual attempting to enforce the federal diesel exhaust fluid mandate, with penalties escalating for repeated offenses. The bill also repeals a previous 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.