German car maker Daimler says it is voluntarily recalling three million diesel cars in Europe to improve their emissions performance.
The Stuttgart-based company, which makes Mercedes-Benz luxury cars, says it is taking the step to reassure drivers and strengthen confidence in diesel technology.
Diesels have been under a cloud since Daimler's competitor Volkswagen admitted equipping vehicles with illegal software that meant they passed emissions tests, but then exceeded limits in everyday driving.
Daimler chief executive Dieter Zetsche said: "The public debate about diesel engines is creating uncertainty - especially for our customers."
The recall will cover nearly all vehicles made under the EU5 and EU6 emissions standards and will start in the next few weeks.
The company said it will cost €220m, but customers will not pay anything.
There has been a push for diesel bans in some German cities because of concerns about levels of nitrogen oxide emitted by the engines.
The Daimler announcement came hours after the regional government in the company's home region of Baden-Wuerttemburg agreed to abandon proposals to restrict diesels if older engines could be mechanically fixed to pollute less, the dpa news agency reported.
Daimler said in May that German investigators had searched its offices in connection with investigations of Daimler employees because of suspicion of fraud and criminal advertising relating to the possible manipulation of exhaust controls in cars with diesel engines. The company has said it is co-operating with the investigation.