Volkswagen engineers have told investigators that certain petrol engines in VW, Audi and Porsche vehicles can be used to manipulate emissions tests, Sunday paper Bild am Sonntag said.
A spokesman for Volkswagen - the parent company of Audi and Porsche - said VW would not comment on an ongoing investigation, adding that the company in recent months had held intensive talks with the Federal Motor Transport Authority.
"There are no new circumstances here," he said.
Gearboxes and software could be manipulated so that vehicles show lower levels of carbon dioxide (CO2) emissions and fuel consumption, Bild said, citing internal documents and witnesses statements.
The news, if confirmed, could add a new dimension to VW's emissions scandal, which has cost the carmaker 27 billion euros ($31.3 billion) in penalties and fines for systematic manipulation of diesel-powered cars to mask excessive pollution levels.
In Europe, vehicles are taxed according to their levels of polluting CO2 emissions.