An anonymous reader writes: A number of news outlets are reporting a breaking story where German authorities investigating the Volkswagen emissions scandal appear to have found documents indicating that German car giants like Daimler, BMW, Volkswagen, Porsche and Audi have been colluding with each other illegally going back at least as far as the 1990s. Representatives and engineers of various German car makers, which were supposed to be competing with each other, apparently met in secret several times a year and agreed on everything from what kinds of cars, engines and automotive tech is created, to how the international market and supply chain for German cars should work. The emissions scandals that have plagued German car makers recently also appear to be the product of this cartel — the cartel members may have decided together to produce cars that try to trick emissions test equipment into believing that not very eco-friendly cars are in fact eco-friendly. It appears that some of these companies may now have come forward and admitted guilt to German investigators to avert huge penalties — but not the general public yet. German investigative news magazine Der Spiegel, which first broken the story of this scandal is reporting: "The five carmakers have been 'co-ordinating the development of their vehicles, costs, suppliers and markets for many years, at least since the Nineties, to the present day', apparently basing the information on the content of the not-to-the-public Volkswagen admission. The Der Spiegel report cites an example of the carmakers agreeing to limit the operation of convertible roofs while a car is moving to speeds up to 30mph (50km/h). The most damaging allegations concern diesel emissions. The five carmakers agreed to limit the amount of a chemical cleaning agent they fitted, in order to save costs and space, the report claims. The agent in question, AdBlue, filters some of the most harmful emissions from diesel engines. Before the agreement, some of the carmakers were testing AdBlue tanks as large as 35 litres (1,232 fl oz) on their cars, which could clean emissions for up to 30,000km. But in 2006 the carmakers agreed to limit AdBlue tanks to just 8 litres, which can effectively clean emissions for less than 6,000km, the report alleges.