Senior US District Judge Charles Breyer said he wanted to know the timing of the fix and any planned payments to vehicle owners by a court hearing set for today.
That is when a deal is expected to be announced between Volkswagen, the US government and private lawyers for the automaker to buy back some of the vehicles and spend just over USD 1 billion to compensate owners, a person briefed on the matter said.
Those plans, and the cost of the fixes, apparently are still under negotiation.
Compensation for car owners was among the details Breyer was seeking, but the judge was more focused on ending the ongoing pollution by getting the vehicles to comply with clean air laws.
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He said last month that issue at the very least "must be resolved" and threatened a trial this summer if Volkswagen didn't meet his deadline. It was unclear whether the deal would satisfy Breyer.
With USD 1 billion to spend, it works out to about USD 1,700 per car. But some owners of newer models who get just a software fix may receive little. About 325,000 owners of older cars that require more extensive repairs likely will get more, because the repairs could affect mileage and performance.
Shares in Volkswagen were up 5.6 per cent in early trading in Europe on news of a deal with the government.
Volkswagen told its shareholders last year it had set aside USD 7.3 billion to help defray the potential costs of a recall or regulatory penalties. Most outside observers have said that figure is likely far too low. The company faces as much as USD 20 billion in fines for Clean Air Act violations alone, before paying to fix the cars or compensate their owners.