A day before Audi’s announcement, BMW said it would offer to upgrade the software in more than 350,000 vehicles. The BMW chairman said the company believed “there are more intelligent options than driving restrictions,” referring to the European cities — including Munich, where BMW is based — that have considered banning or restricting diesel vehicles.
Daimler announced on Tuesday that it would modify three million Mercedes vehicles in Europe to reduce their diesel emissions. None of the companies described the moves as recalls.
European carmakers have heavily promoted the use of diesel vehicles in Europe and the United States to help meet rules on carbon dioxide emissions. But the nitrogen oxides that diesel engines emit are considered carcinogens, and can cause asthma. The cost to automotive companies of installing equipment to neutralize the fumes emitted by diesel vehicles is also increasing, making it difficult to keep the price of the cars competitive.
As German automakers face scrutiny, the government of Chancellor Angela Merkel has also been accused of coddling the powerful car companies and of ignoring signs of the problem.
The companies are trying to avoid repeating the mistakes of Volkswagen, which covered up its use of so-called defeat devices that could adjust emissions to comply with regulations when a car was being tested, but ease back in normal driving conditions.
Several Volkswagen executives have been charged in the United States, and others are under investigation on both sides of the Atlantic. Last month, the former head of thermodynamics at Audi’s engine development department was arrested in Germany. The former manager, Zaccheo Giovanni Pamio, is Italian, and therefore is not protected from extradition and could face trial in the United States.
Early this year, Audi was swept up into a German criminal investigation involving Volkswagen after the authorities accused Audi of installing a system to evade emissions rules in Europe, broadening an inquiry that had focused on the United States.
The inclusion of Audi in the investigation could weigh heavily on Volkswagen: The luxury carmaker accounts for a disproportionate share of Volkswagen’s profit.