Volkswagen, facing tens of billions of dollars in compensation and fines after admitting to manipulating diesel emissions in 2015, reported the cartel to German competition authorities in a letter seen by the weekly, as did Mercedes- Benz maker Daimler.
"The German car industry agreed in secret working groups about technology in their vehicles, costs, suppliers, markets, strategies and even about the emissions treatment of their diesel vehicles," the magazine reported.
Such cooperation between all of the country's large car manufacturers could have included "behaviour infringing antitrust law," according to the Volkswagen letter.
BMW and Daimler similarly declined to comment.
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More than 200 employees of the carmakers formed 60 working groups covering "all areas of car development, petrol and diesel engines, brakes, transmissions and gearboxes... As well as choice of suppliers and prices for parts," an excerpt of the report read.
Since 2006, there had also been "innumerable meetings" about diesel exhaust processing designed to reduce emissions of harmful nitrogen oxides (NOx).
Carmakers agreed to install only small tanks of a treatment solution, AdBlue, used to convert the gases into harmless water and nitrogen, as larger tanks would have been more expensive.
Volkswagen admitted in September 2015 to installing software in 11 million cars worldwide that reduced NOx emissions when it detected cars were undergoing regulatory tests.
In real on-road driving, levels of the harmful gases could be many times higher.
More recently, authorities' suspicion fell on Mercedes- Benz and Smart maker Daimler, with investigators raiding sites belonging to the group in late May.
The Stuttgart-based firm recalled some three million cars earlier this week for a software update designed to reduce emissions.