BMW has rejected reports in the German media that it and other German OEMs worked together to fix the design and lower the cost of diesel emissions treatment systems.

Der Spiegel reported that BMW, Daimler, VW, Audi and Porsche may have colluded to fix the prices and designs of diesel emissions treatment systems. The report said the collusion between the makers in secret working groups has been going in since the 1990s.

The Der Spiegel report alleged that at 'countless meetings', they discussed how large the tanks for AdBlue should be. Large tanks, it said, would have been more expensive and the carmakers agreed on small tanks. However, insufficient AdBlue was held in the tanks to clean emissions of harmful NOx, the report suggests - thus necessitating a fix. The working groups also focused on the selection of suppliers and the setting of costs for vehicle components, it is alleged.

"Cars of the BMW Group are not being manipulated and are in line with the applicable legal requirements," BMW said in a statement, according to Reuters.

Reuters reported that the European Commission's antitrust regulators are investigating the allegations, which have emerged following investigations and interviews with VW Group.

BMW said, according to Reuters, that  it rejected accusations its diesel cars with Euro 6 engines do not provide adequate exhaust treatment because the AdBlue tanks - that inject urea solution as part of the process - are too small.

BMW maintains that its solution combines AdBlue tanks with catalytic converters to lower harmful NOx concentrations, fulfilling all requirements and meaning that no vehicle recalls or software upgrades for Euro 6 engines are necessary.

Reuters reported that BMW also said talks with other manufacturers about AdBlue tanks had been aimed at creating an infrastructure for operating them across Europe.

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