America's Environmental Protection Agency (EPA) says it has written to vehicle manufacturers notifying them it will add to its confirmatory testing, additional evaluations designed to look for potential defeat devices.

It is as yet unclear what the additional measures will be, but the move follows the EPA's sending of a Notice of Violation of the Clean Air Act to Volkswagen, Audi and Volkswagen Group of America.

“These cars contain software that turns off emissions controls when driving normally and turns them on when the car is undergoing an emission test,” said an EPA statement.

“Known as a 'defeat device,' this design feature results in the cars emitting up to 40 times the amount of NOx emissions the standards allow. NOx standards are in place to ensure public health is protected.”

The EPA notes the diesel vehicles affected are as follows: 

  • Jetta (MY 2009 – 2015)
  • Jetta Sportwagen (MY 2009-2014)
  • Beetle (MY 2012 – 2015)
  • Beetle Convertible (MY 2012-2015)
  • Audi A3 (MY 2010 – 2015)
  • Golf (MY 2010 – 2015)
  • Golf Sportwagen (MY 2015)
  • Passat (MY 2012-2015)