US investigators are looking into whether Mercedes parent company Daimler used illegal software to cheat emissions tests on diesel vehicles in the US, according to German newspaper Bild am Sonntag, whose report was picked up by Reuters. Though the investigation itself is not new—it was reported as early as April 2016 that the Department of Justice was looking into Daimler's actions around emissions testing its diesel vehicles—the new reports of emissions-cheating software draw parallels to Volkswagen's notorious emissions scandal.

The German paper allegedly saw documents indicating that one software function on Daimler diesel vehicles turned off the car's emissions control system after driving just 26 km (16 miles). Another program apparently "allowed the emissions cleaning system to recognize whether the car was being tested based on speed or acceleration patterns," according to Reuters.

Software that turns an emissions control system on and off depending on whether the car is being tested in a lab or not is called a "defeat device," and unless the automaker gets explicit permission to have one, a defeat device's inclusion in an auto system is illegal in the US. In 2015, Volkswagen Group was discovered to have hidden defeat device software on its VW, Audi, and Porsche diesels. The automaker has since spent billions of dollars in buying back vehicles that were emitting up to 40 times the allowable amount of nitrogen oxide (NO x ).

Ars asked Daimler for comment, and we'll update this article if we receive a response. To Reuters, the company declined to comment beyond stating that it was cooperating with US authorities. "The authorities know the documents and no complaint has been filed,” a spokesman told Reuters. “The documents available to Bild have obviously selectively been released in order to harm Daimler and its 290,000 employees.”

Among the documents, Bild am Sonntag reported, were emails from Daimler engineers "questioning whether these software functions were legal."

If Daimler were to be found guilty of installing defeat devices on its vehicles, financial repercussions for the company would likely be smaller than what VW Group experienced, as Daimler has sold fewer diesel vehicles in the US than VW Group.