FRANKFURT — The German carmakers BMW and Daimler said on Wednesday that they had taken action against executives involved in an organization that sponsored emissions experiments on monkeys, as the companies tried to squelch a public outcry that threatens to tarnish the image of Germany’s most important exports.

The executives, who were not publicly identified, belonged to the board of an organization established by BMW, Daimler and Volkswagen. The group commissioned research intended to play down the health risks caused by diesel exhaust.

Details of the research, reported last week by The New York Times, have called attention to questionable methods employed by the car companies in trying to influence the public debate. On Tuesday, Volkswagen said it had suspended its chief lobbyist, Thomas Steg, amid the mounting furor over the experiments.

Even before the monkey research came to light, the carmakers had been struggling to stem a decline in diesel vehicles’ share of the European market, which is at its lowest point in a decade.