There has been growing scrutiny of diesel vehicles since Volkswagen admitted in 2015 to installing secret software on 580000 US vehicles that allowed them to emit up to 40 times legally allowable emissions while meeting standards when tested by regulators.
Daimler, which faces ongoing investigations by US and German authorities into excess diesel emissions, said investigations could lead to significant penalties and recalls.
Bild am Sonntag newspaper said the documents showed that US investigators had found several software functions that helped Daimler cars pass emissions tests, including one which switched off emissions cleaning after 26km of driving.
Another function under scrutiny allowed the emissions cleaning system to recognise whether the car was being tested based on speed or acceleration patterns.
Bild am Sonntag also cited emails from Daimler engineers questioning whether these software functions were legal.
A Daimler spokesperson declined to comment on the content of the documents, saying the German company was fully co-operating with the US authorities and had agreed upon strict confidentiality with the Department of Justice.
“The authorities know the documents and no complaint has been filed,” the spokesperson said.
“The documents available to Bild have obviously selectively been released in order to harm Daimler and its 290000 employees.”