Germany's motor vehicle authority is investigating Daimler on suspicions that 60-thousand Mercedes-Benz cars used software that tricked emissions tests.
A spokesman for Daimler said the automaker was reviewing the facts and fully cooperating with the agency.
Daimler previously recalled three million vehicles to fix excess emissions coming from their diesel engines.
It said the company had complied with the German Transport Ministry's regulations when updating software for the recalled vehicles.