EPA expands diesel defeat device probe to Audi, Porsche

Investigators are also looking at diesels built by other automakers.

The Environmental Protection Agency (EPA) has announced it will examine other diesel engines built by the Volkswagen Group to determine whether they're fitted with an illegal defeat device designed to cheat on an emissions test.

The probe now includes the 3.0-liter V6 TDI engine that is offered on the Audi Q5, A6, A7 and A8, on the Volkswagen Touareg as well as on the Porsche Cayenne. Porsche previously wasn't affected by the Dieselgate scandal, but Audi was already included in the first probe, which affects cars like the A3 that are equipped with the 2.0-liter TDI mill.

The EPA is also examining all diesel-powered 2016 Volkswagen models, including the Golf, the Golf Sportwagen, the Beetle, and the recently-updated Passat. Officials have banned the Wolfsburg-based car maker from selling diesel-burning 2016 cars until executives can prove that they are fully compliant with U.S. emissions laws.

U.S. investigators have started to screen diesel-powered models sold by other automakers, but so far they have not detected the presence of a defeat device. BMW and Mercedes-Benz have repeatedly stressed that their cars are clean and completely legal.

In Germany, Volkswagen shares fell nearly 20 percent, wiping €14 billion (approximately $15.6 billion) from its market cap.