Software allowing six-cylinder Volkswagen diesel engines to cheat on pollution tests is on more models than was originally thought, US environmental regulators have said.
The Environmental Protection Agency (EPA) accused VW on November 2 of putting the software on about 10,000 Volkswagen and Audi vehicles with three-litre engines from the 2014 to 2016 model years.
But on Thursday, the German car-maker told the EPA and California Air Resources Board that the same software is on vehicles going back to the 2009 model year.
The EPA said in a statement that it will investigate and take appropriate action.
Volkswagen has denied that the software allows the cars to cheat on emissions tests.