By Chris Isidore
NEW YORK (CNNMoney) -- Diesel cars from Volkswagen and Audi cheated on clean air rules by including software that made the cars look cleaner than they actually were, according to federal and California regulators.
The regulators say that the software on the cars turned up the emission controls only when it could tell that the car was being tested.
"The effectiveness of these vehicles' pollution emissions control devices is greatly reduced during all normal driving situations," said the Environmental Protection Agency's notice to the company. "This results in cars that meet emissions standards in the laboratory or testing station, but during normal operation, emit nitrogen oxides at up to 40 times the standard."
There are nearly 500,000 of the diesel cars on U.S. roads. The models include the VW Jetta, the Beetle and the Golf from model years 2009 through 2015, the Passat from 2014-2015 as well as the Audi A3, model years 2009-2015. The luxury brand is owned by Volkswagen.
Owners of the affected cars do not face health risks according to the EPA and can to continue to drive or sell the cars. But the EPA says that VW will be responsible for fixing the problem.
Volkwagen did not immediately respond to a request for comment.
TM & © 2015 Cable News Network, Inc., a Time Warner Company. All rights reserved.