Russelsheim - German police raided Opel's headquarters on Monday, amid reports that the German carmaker is the latest suspect in the so-called 'dieselgate' scandal.
"We confirm that there are police measures and they are ongoing," a spokesman for police in Hesse state told AFP.
Citing charges from the federal KBA transport authority, tabloid-style Bild daily reported that the raid was related to some 95 000 diesel vehicles built between 2012 and 2017 that may have been fitted with "illegally manipulated" software.
Ever since Volkswagen admitted in 2015 to fitting 11 million cars worldwide with software to make cars appear less polluting in the lab than in real on-road driving, the 'dieselgate' scandal has left few corners of Germany's mighty car industry untouched.
But it has taken longer for Opel - bought last year by Peugeot maker PSA from General Motors - to fall under suspicion than bigger names such as BMW and Mercedes-Benz parent Daimler.
Opel acknowledged in a statement that there were "preliminary proceedings on emissions" with searches at its factories in Russelsheim and Kaiserslautern.
Opel added that it was "fully cooperating with the authorities" and "reaffirms that its vehicles comply with the applicable regulations".