A federal judge overseeing hundreds of class-action lawsuits against Volkswagen says he wants a firm answer within a month about how the German automaker plans to bring nearly 600,000 diesel cars into compliance with clean air laws, according to AP. U.S. District Court Judge Charles R. Breyer told Volkswagen's lawyers at a hearing in California on Thursday that he expects them to report back by March 24. The judge said that by then, he wants to know from the company about the available technical solutions to fix the cars and the status of negotiations on a potential settlement with affected owners. Volkswagen admitted to U.S. regulators in September it had used illegal software installed in its so-called "Clean Diesel" engines. The cheating allowed cars to pass laboratory emissions tests while spewing levels of harmful nitrogen oxide at up to 40 times the level allowed when operating on real roads. Breyer said six months is long enough for VW to find a fix. The judge also stressed that every day the vehicles remain on the road, excess pollution is going into the atmosphere and Volkswagen owners are stuck with cars they can't sell.