Fiat Chrysler Automobiles (FCA) is being investigated for potential emissions cheating by authorities in Germany, Switzerland and Italy.
The car maker’s offices, including those of truck maker CNH, were raided following claims that some of its engines produced illegal levels of emissions.
Potentially illegal software was allegedly detected in Multijet diesel engines used in Alfa Romeo, Jeep and Fiat cars, plus Iveco and Fiat commercial vehicles.
Prosecuters claim that more than 200,000 vehicles could be affected in Germany alone.
Affected engines include Euro 5 and 6 variants of the 1.3-litre, 1.6-litre and 2.0-litre Multijet diesel engine.
A statement from Eurojust, a European Union agency for criminal cooperation across member states, said: "Defeat devices are illegal according to the European Union regulations in place. Vehicles with defeat devices are not approved for road usage in the EU and consumers with such devices installed in their cars face possible driving bans."
The probe is said to be looking into a "number of people" who may have been involved in allegedly allowing use of the devices.
An FCA spokesman confirmed that a number of the company's offices in Europe were visited by investigators in the context of a request for assistance by magistrates in Germany. The spokesman said the business is cooperating fully with authorities.
FCA and CNH Industrial are both controlled by Exor, the holding company of Italy's Agnelli family.
Renault and Nissan were recently accused of emissions cheating following allegations made against Mercedes-Benz.