VW diesel vehicles violated emissions rules, EPA says - Volkswagen AG purposely eluded federal emissions requirements in about half-million diesel cars in the U.S. since 2009 by developing vehicle software that activates anti-pollution controls during testing, regulators said Friday.

The device allowed the German automaker to avoid requirements in selling 482,000 diesel 2009-2015 cars and let them emit 10 to 40 times allowable pollution, environmental officials allege.

The Environmental Protection Agency and California's Air Resources Board said VW violated federal law and could face fines of up to $18 billion ? $37,500 per vehicle ? as well as criminal prosecution. Both agencies dispensed notices of non-compliance to VW Friday, a step necessary before ordering a recall.

In a statement, VW said it is working together with the government, but didn't say if it has accepted wrongdoing.

Most U.S. VW dealers don't have any remaining 2015 diesel cars to sell. VW is not allowed to sell any remaining 2015 vehicles until "they get answers to the questions of how these vehicles are being operated. Volkswagen couldn't explain why we're getting these excess emissions," said Christopher Grundler, director of the EPA's Office of Transportation of Air Quality.

The Justice Department is likely to start a criminal investigation. The EPA said it "expects to compel VW to issue a recall in the future to reduce the emissions impacts of these vehicles."

Friday's development raises questions if other automakers, including General Motors Co., BMW AG and Mercedes-Benz USA, were affected because they had to follow diesel emissions rules.

The EPA said it is waiting to see if other automakers are breaking the rules with diesel vehicles.