UPDATE: Our colleagues at Consumer Reports have decided to suspend the “Recommended” ratings it had previously given to the Passat diesel and Jetta diesel.

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The federal government on Friday ordered Volkswagen to recall nearly 500,000 vehicles over concerns the automobiles expose people to harmful pollutants. Unlike most recalls handed down by government agencies, this one didn’t come from the National Highway Traffic Safety Administration. Instead, it came from the Environmental Protection Agency.

The EPA initiated the recall through a notice of violation [PDF] of the Clean Air Act, after an investigation found the automaker intentionally installed software in 482,000 diesel 4-cylinder model year 2009 to 2015 Volkswagen and Audi vehicles as a way to evade emissions standards for certain pollutants with a range of serious health effects.

The software – known as a defeat device – was first detected during independent analysis by researchers at West Virginia University who were working with the International Council on Clean Transportation, a non-governmental organization. The findings raised questions about emissions levels, and the EPA, along with the California Air Resources Board, began further investigations into the issue.

“Using a defeat device in cars to evade clean air standards is illegal and a threat to public health,” Cynthia Giles, Assistant Administrator for the Office of Enforcement and Compliance Assurance, said in a statement.

According to the notice, the “sophisticated software algorithm” in the vehicles is programmed to detect when the car is undergoing official emissions testing, and to only turn on full emissions control systems during that testing.

However, the effectiveness of these vehicles’ pollution emissions control devices is greatly reduced during all normal driving situations.

“This results in cars that meet emissions standards in the laboratory or testing station, but during normal operation, emit nitrogen oxides, or NOx, at up to 40 times the standard,” the notice states.

Under the Clean Air Act, vehicle manufacturers are required to certify to the EPA that their products will meet applicable federal emission standards to control air pollution, and every vehicle sold in the U.S. must be covered by an EPA-issued certificate of conformity.

Motor vehicles – such as the Volkswagen models in question – equipped with defeat devices, which reduce the effectiveness of the emission control system during normal driving conditions, cannot be certified.

“By making and selling vehicles with defeat devices that allowed for higher levels of air emissions than were certified to EPA, Volkswagen violated two important provisions of the Clean Air Act,” the EPA alleges.

Models covered by the recall include the model year 2009 to 2015 Volkswagen Jetta, Beetle, Golf, and Audi A3, as well as model year 2014 to 2015 Volkswagen Passat sedans.

“It is incumbent upon Volkswagen to initiate the process that will fix the cars’ emissions systems,” the EPA says. “Car owners should know that although these vehicles have emissions exceeding standards, these violations do not present a safety hazard and the cars remain legal to drive and resell.”

Consumer advocacy groups were quick to praise the agencies for their efforts to ensure automakers meet standards put in place to protect consumers.

“Volkswagen was ripping off the consumer and hurting the environment at the same time,” Ellen Bloom, senior director of federal policy for our colleagues at Consumers Union, said. “It’s outrageous. We applaud the EPA and California for cracking down on Volkswagen. These actions send a powerful message that if a carmaker uses technology to get around the rules, regulators going to come down hard on you for breaking the law.”

Friday’s order comes more than a year after the EPA and CARB imposed a record $100 million penalty against Hyundai and Kia for not being completely truthful about their vehicles’ fuel economy estimates.

The EPA charged that the automakers overstated fuel economy figures by an average of six miles per gallon for the Hyundai Accent, Elantra, Velostar and Sante Fe, as well as the Kia Rio and Soul.

The complaint filed jointly by the United States and the California Air Resources Board alleges that Hyundai and Kia sold close to 1.2 million cars and SUVs whose design did not conform to the specifications the companies certified with the agency.

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