Citing “matching information” from several anonymous sources, daily Sueddeutsche Zeitung and broadcasters NDR and SWR reported that Daimler took the case to the authorities “significantly sooner” than Volkswagen, which reportedly turned to them in July 2016.
Under European rules, the first firm to reveal evidence of a cartel can escape a fine.
A spokesman for Daimler declined to comment on the report.
A cloud has hung over Germany's auto industry since weekly Der Spiegel reported Friday on documents it said showed carmakers held secret meetings since the 1990s.
Daimler, BMW, and VW with its Audi and Porsche subsidiaries were all involved in the talks to agree on technology, suppliers, markets, strategies and polluting emissions, the magazine reported.
Both the European Commission and Germany's competition authority say they have received information relating to the alleged cartel, which is now “undergoing examination” in Brussels.
The European Union's executive arm has the power to inflict heavy fines on firms found to be infringing cartel rules.
Daimler has already been in its sights over one cartel case, paying €1.1 billion last year over price-fixing between its truck division and three other European manufacturers.
Volkswagen has made no comment on the allegations ahead of a supervisory board meeting Wednesday, while BMW has denied any wrongdoing and Daimler has said it holds fast to an internal competition law compliance scheme.
Shares in Mercedes-Benz and Smart manufacturer Daimler rose slightly Tuesday on the media reports, gaining 0.21 percent to trade at €61.05 around 1130 GMT.
Daimler's gains fell short of the DAX index of blue-chip German shares, but contrasted with losses for shares in Volkswagen and BMW.