A spokeswoman at the prosecutor’s office told French media on Friday that the probe of the German car maker’s operations is over charges of aggravated deception, as several complaints have been announced in France by the French owners of Volkswagen diesel cars and shareholders in the VW auto group.
French consumer protection and fraud control authorities have launched a separate investigation, the results of which are expected by December.
Several countries, including the United States, have launched similar judicial investigations after Volkswagen admitted that some 11 million diesel cars worldwide are fitted with the device, which turns off pollution controls when the vehicle is being driven and turns them on only when it detects that the car is undergoing an emissions test.
VW's French unit said last week that 984,064 vehicles sold in France over the past few years - including VW, Audi, Skoda and Seat – were fitted with the software.
France began randomly testing around a hundred diesel cars on Thursday.
The World Health Organisation in 2012 declared emissions from diesel engines to be carcinogenic. The French probe, which will only concern cars in France, was opened due to this danger to public health, according to French news agency AFP.
The French government called last month for a Europe-wide probe of all carmakers, while American and European regulators have said they are working on tighter rules and more stringent checks of pollution from vehicles.
The EU is seeking to decide on "coordinated action" by the end of November based on the various investigations in its member states, Industry Commissioner Elzbieta Bienkowska told journalists on Thursday.