In Europe, Volkswagen led the way in civilizing diesel for mass-market passenger cars in the 1990s. The company produced engines that were less noisy and less smelly than diesels of old, yet offered excellent acceleration and fuel economy.

Volkswagen used diesel as a competitive advantage against rivals like Toyota or General Motors’ Opel, which were slower to invest in diesel. “The market shares over the years changed drastically, mostly on the back of diesel,” said David J. Herman, the former chairman of Opel.

Now that diesel is under attack, German carmakers are being forced to put more emphasis on hybrid vehicles, a technology pioneered by Toyota. Volkswagen has promised to invest in clean technologies as part of a legal settlement in the United States, though the details of the investment are still being determined.

Volkswagen remains the company hurt most by the diesel fallout. Only Volkswagen made “clean diesel” the focal point of its marketing in the United States. The diesel push exposed the company to stricter American government regulations and enforcement, and a judicial system more accommodating to class-action lawsuits by customers.

Rivals like Daimler, G.M. and Fiat Chrysler sell diesels in the United States but in much smaller numbers. However, Daimler, the maker of Mercedes-Benz cars, is also in the cross hairs of federal enforcers. It has said it is conducting an internal investigation in response to questions from the Department of Justice about its emissions in the United States.

Recent studies by the German and British governments found no proof that any carmakers other than Volkswagen had equipped cars with illegal software intended to fool emissions tests.

The other manufacturers simply took advantage of rules allowing them to reduce emissions controls to protect the engine under certain conditions, such as colder weather. The carmakers argued that lower temperatures could cause condensation and a buildup of soot in a major component of the emissions control system, causing it to fail.