The software update will not initially be available in the United States. Jörg Howe, a Daimler spokesman, said the company was in talks with the United States Department of Justice, the Environmental Protection Agency, and the California Air Resources Board. The agencies have been investigating Daimler emissions. The company is also the subject of a criminal investigation in Germany, although no suspects have been identified.
A software update, which Daimler said would take about an hour, will cause the emissions controls to operate under a broader set of conditions. Previously, the pollution equipment was programmed to operate at maximum effectiveness only under a narrow range of temperatures. That range will be expanded.
The software update is part of an effort to combat a widening inquiry and a public backlash over allegations that it evaded rules controlling vehicle pollutants. The move, which Daimler declined to call a recall, is being made as the company faces investigations over the diesel deception accusations.
Daimler has been under increasing pressure in Germany since media reports last week suggesting the scale of the emissions problem was greater than previously known. While the company denies doing anything illegal, last week its managers were summoned to Berlin for talks with officials about emissions.
Chancellor Angela Merkel of Germany is under pressure amid criticism that her government has long coddled carmakers and ignored signs that nearly all diesel vehicles in Europe emit more harmful nitrogen oxides in normal use than regulations allow.
“To effectively improve the emissions of additional model series, Daimler has now decided to extend the service action to include over three million Mercedes-Benz vehicles,” the company said in statement. It said the measures would be rolled out in the coming weeks and would cost about 220 million euros, or $252 million.