BMW, which said its Ebit margin may be as much as 1.5 percentage point lower than its target for at least 6 per cent this year, may suffer worst from any fine.
Daimler said it doesn't expect a fine because it was the first to tell the EU about the cartel, it said in an emailed statement. Volkswagen has previously said it sought a fine reduction for helping regulators and said Friday it will review the EU's objections and respond as part of its cooperation with authorities.
A maximum fine may be "in the area of high triple-digit millions," Evercore ISI analysts wrote in a research note Friday. "BMW could be hit particularly hard," they said.
The probe represents another challenge for the German auto industry, which is grappling with the fallout from revelations in 2015 of VW's diesel-cheating and the disruptive shift to self-driving, electric cars.
Allegations of a cartel emerged in Germany's Spiegel magazine, which reported that VW, Daimler and BMW met starting in the 1990s to coordinate activities related to vehicle technology, costs, suppliers and strategy as well as diesel-emissions controls.
VW has put aside some €29b to settle diesel emissions-related lawsuits and pay damages, and faces more than US$10b ($14.8b) in further claims from disgruntled investors and customers - as well as untold damage to its reputation as top executives risk being hauled before court.
At the same time, Daimler has agreed to recall some 774,000 vehicles in Europe to improve emissions performance and remains subject to investigations in Germany and the US.
BMW has agreed to pay a 10 million-euro fine after an investigation found the company had installed the wrong emissions software in a limited number of vehicles by accident.