Three million Mercedes-Benz owners in Europe will be offered a software fix for their diesel cars.
Daimler, which owns the luxury car maker, has been under intense pressure from police and prosecutors.
Authorities are investigating the possible manipulation of diesel exhaust emissions in passenger cars.
A Daimler spokesman said the software fix, which will cost about 220m euros (£195m), was not linked to the police investigation.
He said the “voluntary service measure” was to cut nitrogen oxide pollution.
“The service actions involve no costs for the customers. The implementation of the measures will be starting in the next weeks,” Daimler said.
The measures come after German MPs last week questioned Mercedes-Benz executives about emissions.
At the time the carmaker agreed with the transport ministry to undergo another round of emissions tests.
In May German police searched 11 offices of the carmaker as part of an investigation into possible fraudulent emissions data by employees.
A total of 23 prosecutors and 230 police officers took part in the search in the states of Baden-Wuerttemberg, Berlin, Lower Saxony and Saxony.