Germany's carmakers face a tough new reality. A sector that employs some 800,000 people and dominates global sales of luxury cars has long been an object of national pride: not just a symbol of the country's postwar industrial success, but more or less synonymous with Germany Inc.

Politicians have been swift to defend its interests, but the backlash against diesel is changing attitudes. At a national “diesel summit” in Berlin on Wednesday, carmakers pledged to upgrade 5m cars to reduce harmful emissions.

That promise may not be sufficient. In the past week, the government has ordered a recall of a Porsche model found to contain emissions-cheating software. Amid popular discontent, Conservative politicians are preparing to drop their opposition to class action lawsuits of the kind that Volkswagen has faced in the US.

As serious as the debate over the industry's proximity to government are claims that carmakers have also been too cosy with each other. As the magazine Der Spiegel reported last month, the EU Commission has launched a cartel investigation into VW, Daimler and BMW, as well as VW units Porsche and Audi, which have been meeting regularly in working groups since the 1990s to discuss technology and components ranging from brakes and clutches to diesel emissions cleaning systems.

The financial consequences could be considerable, if the five companies are found to be in breach of EU competition rules. Beyond the possibility of fines or reputational damage, though, the investigation raises questions over the unusually collaborative nature of German corporate culture, which has been a key ingredient in its manufacturing and export success.

Germany industry is widely admired for its success in building long-term relationships with suppliers and research institutes. Companies also have a long tradition of co-operating with others in the same sector to boost efficiency and international competitiveness. Such collaboration can be both acceptable and desirable, if it helps to set standards, drive innovation, ensure interoperability and bring down costs for consumers.

The question is whether this culture of collaboration made the companies involved more liable to cross the line into collusive, anti-competitive practices. BMW contests any such suggestion, saying it co-operates only on components that do not affect brand differentiation. However, Daimler and VW — which both volunteered information to regulators — are clearly worried that some parts of their discussions may not stand up to close scrutiny.

The extent of wrongdoing — in particular, any attempt to fix prices — is unproven. However, the exclusion of foreign rivals looks suspicious, and allegations that the companies agreed to purchase emissions cleaning systems that have turned out not to be adequate in real-world driving conditions are worrying. The hope must be that the commission holds the companies to account for past practices, and gives clarity on the limits to collaboration for the future. That matters for other sectors in Europe as well as Germany's auto industry.

Having bet heavily on diesel, Germany's carmakers need to press ahead with electric technology and to adapt their businesses to the rise of car sharing. This is not only a challenge for them. In a heavily regulated industry, politicians and governments have to facilitate the retreat from diesel. But even when the pressure of the autumn federal election has eased, an angry public is unlikely to let automakers shirk responsibility.