German car maker Audi is to fit up to 850,000 diesel cars with new software to improve their emissions performance.
Audi, a unit of Volkswagen, said it "aims to maintain the future viability of diesel engines" and believes the voluntary retrofitting programme "will counteract possible bans on vehicles with diesel engines".
The free programme, which will apply to Europe and other markets outside the US and Canada, applies to cars with six-cylinder and eight-cylinder diesel engines.
On Tuesday, Daimler said it will voluntarily recall 3 million Mercedes-Benz cars with diesel engines in Europe to improve their emissions performance.
Diesels have been under a cloud since Volkswagen admitted equipping vehicles with emissions-cheating software.