Daimler has hired auditing firm Deloitte Touche Tohmatsu to help with an internal investigation into its diesel-engine emissions technology requested by the U.S. Department of Justice, the automaker said.

Daimler is working with the DOJ and U.S. Environmental Protection Agency to avert a crisis spurred by the EPA’s investigation into Volkswagen’s “defeat device” software that began last fall. Daimler has been conducting an internal investigation of its certification process for diesel exhaust emissions from Mercedes diesel cars sold in the U.S. at the request of the DOJ.

Deloitte staff in Germany have been searching through documents and emails from staff at Daimler’s engine development site in Sindelfingen and its corporate headquarters in Stuttgart, German weekly Der Spiegel previously reported.

SEE ALSO: Daimler Facing its Own Diesel Car Class-Action Lawsuit

In early April, owners of Mercedes-Benz diesel cars filed a class-action lawsuit in a New Jersey federal district court. The suit claimed that the Mercedes BlueTEC is not performing well in real world tests. New tests have shown that diesel cars with the BlueTEC system produced nitrogen oxide emissions in virtually all road tests that were far higher than in controlled lab tests.

The EPA said at the time of the lawsuit filing that it had requested information from Daimler, but it had not opened an official investigation. Daimler is working with the DOJ and EPA to address concerns, and to avoid a recall for fix-it replacements or buybacks of the recalled cars.