On March 16, 2025, Region 10 filed an Expedited Settlement Agreement with STM Tuning for violations of Title II of the Clean Air Act. Between January 1st, 2024 and October 15th, 2025, STM Tuning removed or rendered inoperative emissions-related device or element of design installed on or in a motor vehicle or motor vehicle engine. This is the first enforcement action EPA has taken against STM Tuning for tampering with emission control units and rendering them inoperable. STM Tuning will pay a civil penalty of $13,004.20.