Volkswagen Used 'Defeat Device' To Skirt Emissions Rules, EPA Says

Updated at 2 p.m. ET

The Environmental Protection Agency says Volkswagen intentionally violated the Clean Air Act by using sophisticated software in its diesel-powered cars that detects emissions testing — and "turns full emissions controls on only during the test."

Installed in four-cylinder cars, the software, which the EPA calls a "defeat device" that's meant to trick official tests, allowed diesel Jettas, Beetles and other cars to "emit up to 40 times more pollution" than allowed under U.S. emission standards.

After the automaker was confronted with emission test results this month, the agency says, it admitted that the vehicles contain defeat devices.

Volkswagen must now fix the emissions control systems, the agency says, adding that the automaker could be liable for civil penalties and other punishment. The cars in question are popular Volkswagen and Audi models that were made from 2009 to this year.

The affected four-cylinder, diesel cars include:

• Jetta (model years 2009–2015)
• Beetle (model years 2009–2015)
• Audi A3 (model years 2009–2015)
• Golf (model years 2009–2015)
• Passat (model years 2014-2015)

"Using a defeat device in cars to evade clean air standards is illegal and a threat to public health," said Cynthia Giles, assistant administrator for the Office of Enforcement and Compliance Assurance.

The news that the Volkswagens produce far more pollution than is legal is sure to rattle some VW owners who bought their cars at least in part because of their perceived impact on the environment.

The U.S. government also has reason to feel duped: Volkswagen's "clean diesel" TDI engines earned a $1,300 federal tax credit for people who purchased a Jetta sedan or wagon back in 2009, the first year affected by the recall.

When applied to a base price of around $22,000, the hefty tax credit helped explain why the TDI vehicles were hard to keep in stock.

The cars were first found to produce too much nitrogen oxides, or NOx, by researchers at West Virginia University who were working with the International Council on Clean Transportation, the EPA says. After the WVU analysis found irregular NOx levels in diesel Volkswagens, the EPA and the California Air Resources Board took up their own study.

As for drivers of the cars, the EPA says, "these violations do not present a safety hazard and the cars remain legal to drive and resell."

The agency adds, "Owners of cars of these models and years do not need to take any action at this time."