Germany's transport minister rejected accusations on Wednesday that he had prior knowledge of the emissions control technology used by Volkswagen to rig test results.
"I have made it very clear ... that the allegations of the Greens party are false and inappropriate," Transport Minister Alexander Dobrindt told journalists.
He said experts were now examining how to deal with the millions of cars with such devices.
"Volkswagen has said that this part is not active. The commission will now examine what kind of impact an inactive part can have on the engine. Afterwards, you can decide what will happen with these cars," he said.