WASHINGTON – The U.S. Environmental Protection Agency (EPA) sent a letter to vehicle manufacturers notifying them that the agency is adding to its confirmatory testing additional evaluations to look for potential defeat devices.

EPA issued a notice of violation (NOV) of the Clean Air Act (CAA) to Volkswagen AG, Audi A and Volkswagen Group of America. The NOV alleges that four-cylinder Volkswagen and Audi diesel cars from model years 2009-2015 include software that circumvents EPA emissions standards for certain air pollutants.

California is separately issuing an In-Use Compliance letter to Volkswagen, and EPA and the California Air Resources Board (CARB) have both initiated investigations based on Volkswagen’s alleged actions.

The roughly 482,000 diesel passenger cars sold in the United States since 2008 include:

• Jetta (MY 2009–2015)
• Jetta Sportwagen (MY 2009–2014)
• Beetle (MY 2012–2015)
• Beetle Convertible (MY 2012–2015)
• Audi A3 (MY 2010–2015)
• Golf (MY 2010–2015)
• Golf Sportwagen (MY 2015)
• Passat (MY 2012–2015)

These cars contain defeat device software that turns off emissions controls when driving normally, and turns them on when the car is undergoing an emission test. The cars emit up to 40 times the amount of NOx emissions that Clean Air Act standards allow. EPA and CARB uncovered the defeat device software after an independent analysis raised questions about emissions levels, and further investigations into the issue ensued. In September, after EPA and CARB demanded an explanation for the identified emission problems, Volkswagen admitted that the cars contained defeat devices.

USA Today writes that EPA warned the new testing process could mean it will take longer for automakers to secure certification required to sell new vehicles in the United States. "We aren't going to tell them what these tests are," said Christopher Grundler, director of the EPA Office of Transportation and Air Quality, in a conference call with reporters. "They don't need to know."