The company made the statement after the U.S. Environmental Protection Agency (EPA) and the California Air Resources Board found that the software on VW diesel cars showed false emission data.

　　"The Board of Management at Volkswagen AG takes these findings very seriously. I personally am deeply sorry that we have broken the trust of our customers and the public. We will cooperate fully with the responsible agencies, with transparency and urgency, to clearly, openly, and completely establish all of the facts of this case," Martin Winterkorn, CEO of Volkswagen AG, said in a statement.

　　VW orders investigation into violation of U.S. emission rules

　　The software installed by Volkswagen in its cars has violated the Clean Air Act, said the EPA in a statement on Friday. The software called "defeat device" by the EPA can turn on full emission controls only when the car is undergoing emission tests to make the car meet the legal emission standards, but during normal driving, the car will emit nitrogen oxides at up to 40 times the standard.

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

　　The allegations cover roughly 482,000 diesel passenger cars sold in the United States by Volkswagen AG, Audi AG, and Volkswagen Group of America since 2008. The models include Jetta, Beetle, Golf, Passat and Audi A3.

　　The EPA also said "Volkswagen may be liable for civil penalties," which means the German car maker could face penalties of up to 37,500 U.S. dollars per vehicle, the maximum fine for violating the Clean Air Act, or a total of more than 18 billion dollars.