Nine days remain until the deadline imposed by a judge for Volkswagen and two regulatory agencies to agree on the outline of a plan to modify vehicles affected by the diesel-emission scandal.
That deadline was already postponed once, but whether VW, the EPA, and the powerful California Air Resources Board can come to an agreement on how to update almost 600,000 vehicles remains in doubt.
U.S. District Judge Charles Breyer imposed the original date, March 24, in February, saying, "Six months is enough"—and then postponed it to April 21 at the request of all three parties.
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But EPA administrator Gina McCarthy indicated last week that it remained unclear whether the parties could agree on all necessary points by that time.
She told reporters, according to Reuters, that discussions among the parties were "robust," but that she did not know if the terms of a deal could be reached by the latest deadline.
A full settlement is not required by April 21, but Volkswagen, the EPA, and CARB must all agree to the terms of a plan to update the hundreds of thousands of TDI diesel vehicles.
2012 Volkswagen Passat TDI Six-Month Road Test
Those were marketed by VW, Audi, and Porsche, and subsequently discovered to contain "defeat device" software.
Those vehicles are powered by one of two different 2.0-liter four-cylinder diesel engines or a 3.0-liter V-6 diesel.
About 45 percent of the total are fitted with a Selective Catalytic Reduction (SCR) emission aftertreatment system using urea injection.
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Experts suggest that various software and hardware modifications should be likely to make these cars comply with emission limits under real-world conditions.
The impact on performance and fuel economy remains a key issue, however.
VW's lack of specificity on those effects caused CARB to reject the company's first plan for modifications to the 2.0-liter TDI cars.
Consumer Reports tests 2015 Volkswagen Jetta TDI diesel in 'cheat mode,' October 2015 [video frame]
But 325,000 of the older 2.0-liter cars have no SCR system in place; these are the vehicles with the worst emission excess.
Modifying these vehicles would likely cost several thousand dollars per car—for cars up to seven years old—and perhaps require the cars to be recertified for safety and efficiency, if in fact it is possible at all.
In her meeting with reporters, McCarthy declined to comment on media reports that some of the non-achieving vehicles could be left in operation under a deal in which Volkswagen would agree to other mitigating measures to offset their excess emissions.
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In November, VW offered owners of its 2.0-liter TDI vehicles expanded roadside assistance and a pair of $500 gift cards, one of which could be redeemed only at an authorized Volkswagen dealership.
VW, Porsche, and Audi dealers may not sell any new 2016 diesel models—which were never certified for sale by the EPA—nor Certified Used diesel models from 2009 on.
The company's U.S. sales have fallen in a surging market for new cars, and the value of used TDI vehicles has taken a hit as well.