In 2019, U.S. engine maker Cummins Inc. was facing the largest Clean Air Act penalty ever over accusations of cheating on diesel engine emission tests. The Environmental Protection Agency (EPA) and the Department of Justice (DOJ) alleged Cummins deliberately programmed hundreds of thousands of its engines, installed on truck and buses, to detect when they were being tested and turn on pollution control devices. When the engines were operated under regular driving conditions, however, the devices were turned off. This caused emissions of pollutants like nitrogen oxides to exceed the legal limit.
The EPA and DOJ accused Cummins of violating the Clean Air Act and demanded that the company pay a civil penalty of up to $1.5 billion. The penalty was far larger than any previous penalty for violations of the Act. Cummins denied the allegations and contested the penalties, but ultimately settled the case in 2020 by agreeing to pay a record civil penalty of $2 million and to invest $500 million in new engine technology that would reduce emissions. The settlement also required Cummins to stop selling non-compliant engines and to ensure that emissions standards are met in the future.