BRUSSELS, Sept. 18 (Xinhua) -- The European Commission on Tuesday opened formal investigation into possible collusion between German car makers BMW, Daimler and the VW group (Volkswagen, Audi, Porsche) on clean emission technology.

The "in-depth" investigation aims to assess whether BMW, Daimler and VW colluded, in breach of EU antitrust rules, to avoid competition on the development and roll-out of technology which could reduce harmful emissions from petrol and diesel passenger cars.

"If proven, this collusion may have denied consumers the opportunity to buy less polluting cars, despite the technology being available to the manufacturers," said Margrethe Vestager, the European Commissioner in charge of competition policy.

The Commission said it has no indications at this stage that the parties coordinated with each other in relation to the use of illegal defeat devices to cheat regulatory testing. And the opening of a formal investigation does not prejudge its outcome.

The Commission has informed the companies concerned and the competition authorities of the member states that it has opened proceedings in this case.

There is no legal deadline for bringing an antitrust investigation to an end.