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 are unconstitutional. The Act nullifies any federal regulations related to this requirement and prohibits state agencies from enforcing such mandates. It emphasizes the state's rights under the 10th Amendment of the U.S. Constitution, declaring that the manufacture, sale, and installation of diesel engines that do not require diesel exhaust fluid are lawful within Oklahoma.

Additionally, the Act imposes penalties for any state agency or individual attempting to enforce federal diesel exhaust fluid mandates, including civil fines of up to $5,000 per violation, suspension of enforcement authority, and potential termination for state employees. The bill also repeals a previous law related to emission control systems, specifically 47 O.S. 2021, Section 12-423. The Act is declared an emergency measure, taking effect immediately upon passage and approval.