Volkswagen has declined to comment, and BMW in a statement Sunday denied any involvement in collusion with rival vehicle companies.
"We have therefore decided on additional measures to reassure drivers of diesel cars and to strengthen confidence in diesel technology", he said.
"It is premature at this stage to speculate further", according to the statement from the commission's executive arm.
The goal was to make diesel motors fit for the future, contribute to reducing air pollution and avoid the imposition of driving bans, Audi said in a statement.
On Tuesday, BMW and Audi reached an agreement with the Bavarian state government to voluntarily retrofit its "Euro 5" diesel-engine cars with software that will reduce emissions.
Audi's recall comes days after Mercedes-Benz and Smart maker Daimler issued a voluntary recall for more than three million diesel vehicles in Europe. Audi is aware that the investigations by the KBA have not yet been concluded. Diesel engines, however, have higher nitrogen oxide emission which harms human health and sulfur which harms the environment.
In fact, it is being said that they even agreed to reduce the size of the urea tanks which are used to reduce emissions according to more advanced Euro standards, rendering them ineffective to control noxious fumes.
Speaking of Dieselgate, some investigators have claimed Daimler installed a software cheat device on its cars, kind of like VW. 'What Audi and Mercedes have announced is just the tip of the iceberg, ' he said.
The E.U. Commission is already examining the case, having confiscated documents from the companies involved and calling first witnesses. Several European cities-including Stuttgart, the home of Porsche-have called for a ban on diesel cars, which accounted for around 47% of cars sold (paywall) in Europe's five biggest markets in the second quarter of this year.