Germany's legal system has acted where the politicians couldn't or wouldn't - it ruled on Tuesday that local authorities can ban diesel cars from their roads if pollution levels break the legal limits.
The government opposes the ban but like other EU states, is under pressure from Brussels to get their pollution emissions down to legal levels.
Environment Minister Barbara Hendricks wants to avoid driving bans - instead she's pushing for a "blue sticker" system for clean cars.
"This does not mean that driving bans will come into force overnight. My goal is and remains that driving bans should never have to come into force, because we can manage to keep the air clean in other ways," she told a news conference.
Diesel cars will now have to be modified to make them cleaner - but that's expensive.
Germany's giant car industry has been badly shaken after Volkswagen was caught rigging their diesel emission tests.
And now pressure groups are saying the car manufacturers must foot at least some of the bill.
"A retrofit would start at somewhere around 1500 euros. But here I think it is the moral duty of the car manufacturers, even if just to save their reputation, to contribute to covering the costs wherever possible," said Markus Schape, a lawyer for the German Auto Safety Group.
But it's unclear how it will work in practice - on Wednesday a transport ministry spokesman admitted that the high costs of retrofits meant that the value of the vehicle would have to be taken into acount.