Workers at Porsche and a US subsidiary company are being investigated for suspected fraud and false advertising related to diesel emissions, the Stuttgart prosecutor's office was reported to have said.
In a statement cited by Reuters, Stuttgart prosecutor Jan Holzner said there were grounds to suspect potential fraud and false advertising by Porsche employees, while declining to elaborate given the ongoing nature of the probe.
Porsche told the news agency it was cooperating fully with authorities and had proactively sought contact with prosecutors even before a formal probe was launched.
Illegal software has been found in VW, Audi and Porsche cars equipped with diesel engines, the report noted.
Some Porsche models have Audi-made three litre diesel engines and Munich prosecutors separately are investigating Audi about its role in designing that engine, the report added.
Reuters noted prosecutors last week arrested Audi worker Giovanni Pamio on suspicion of fraud and false advertising. He's in custody and being sought by the US Justice Department for his alleged role directing Audi employees to design software to cheat US emissions tests.