A German court ruled on Wednesday that software updates meant to fix the "dieselgate" emissions cheating in certain Volkswagen models were themselves illegal, dealing another blow to the auto giant.
The ruling marks a victory for German environmental group DUH which had brought the case against the KBA federal transport authority.
The Schleswig-Holstein administrative court agreed with the DUH that the KBA regulator should not have approved the software fixes in 62 diesel models with EA-189 engines across VW's own brand and its Seat and Audi subsidiaries.
The KBA must now take "appropriate measures" to remedy the situation, a court spokeswoman told AFP.
Volkswagen said it would appeal the ruling together with the KBA, adding that there was no risk of vehicles being ordered off the roads, "nor are hardware retrofits necessary".
Volkswagen was plunged into crisis in 2015 following revelations it had installed illegal "defeat devices" in millions of diesel vehicles to make them seem less polluting in the lab than they were on the road.
The software fixes the group has offered since then have themselves come under growing scrutiny, including the so-called thermal window programme that reduces or even deactivates emissions filtering in very cold temperatures.
The European Court of Justice has already found that in many cases the "thermal window" software also constituted a defeat device.
Volkswagen however argues that the "thermal window" serves to protect the car engine from damage at extreme temperatures.
The DUH non-governmental group hailed the latest verdict as a win "for clean air in Germany".
It called for "millions of diesel cars from Volkswagen, Seat and Audi" to be "decommissioned or fitted with a new emissions control system at the manufacturer's expense".
The DUH won a similar case at the same court in Schleswig-Holstein last year, which VW and the KBA are also appealing.
The DUH has launched proceedings against other carmakers as well including Mercedes-Benz, BMW and Fiat, also accusing them of violating emission regulations.
Agence France-Presse