VW Group of North America now owns hundreds of thousands of Volkswagen and Audi TDI diesel vehicles it has bought back from owners under the terms of various diesel emission scandal settlements.

Yesterday, it got some very good news: the EPA has approved a modification that will it allow it to resell the oldest and dirtiest of those vehicles.

Known as "Generation One" diesels, they use the old EA189 2.0-liter turbodiesel engine but were not built with the modern urea-injection emission treatment system.

DON'T MISS: EU investigating diesel collusion among Audi, BMW, Mercedes, Porsche, VW: report

Analysts had largely expected this group of cars to be unfixable, due to the lack of a urea tank and other elements of the selective catalytic reduction system used on modern diesel vehicles to reduce emissions of nitrogen oxides.

But the fix will allow the few owners who choose to keep their vehicles to have them modified, and VW to sell the rest legally as used cars.

The 326,000 Generation One cars represent the largest group among roughly 450,000 2.0-liter 4-cylinder diesel VWs and Audis, sold from 2009 through 2016, that were still on the road at the time the settlement was announced.

2010 Volkswagen Golf TDI

2010 Volkswagen Golf TDI

The approved modification applies to the follow vehicles, whether fitted with automatic transmissions or manual gearboxes:

  • 2009-2014 Volkswagen Jetta TDI
  • 2009-2014 Volkswagen Jetta SportWagen TDI
  • 2010-2014 Volkswagen Golf TDI
  • 2012-2014 Volkswagen Beetle TDI and Beetle Convertible TDI
  • 2010-2013 Audi A3 TDI

The EPA approval letter, also signed by the powerful California Air Resources Board, describes the intent of the modification as "to reduce the NOx pollution from these vehicles."

Thus far, it remains unclear whether the modifications will actually bring the vehicles into compliance with the Tier 2 Bin 5 emission limits under which they were certified.

Those limits, which came into effect as of January 1, 2008, were then among the world's most stringent. The European Union only put roughly similar limits into effect on January 1, 2017.

2009 Volkswagen Jetta TDI

2009 Volkswagen Jetta TDI

The modification that has been approved will affect both hardware and software in the Generation One TDI vehicles.

Volkswagen will replace the "defeat device" software that had limited emissions only during emission testing, replacing it with updated software that keeps the emission-control system active in all "typical" vehicle operations.

The company will also replace the NOx catalyst and, in 2009 models only, additional hardware in the emission-control system.

Test data and technical information submitted by VW, along with tests by the EPA and CARB, according to the statement, have demonstrated that the modifications reduce NOx emissions without affecting the vehicles' durability or reliability.

VW must "thoroughly identify" any differences in vehicle performance, including fuel economy and acceleration, to let the few remaining owners decide whether the modified vehicles still fit their needs.

2013 Audi A3 TDI (European spec)

2013 Audi A3 TDI (European spec)

Buyers who purchase the modified used TDI vehicles from Volkswagen, at least in North America, will receive similar disclosures.

Media reports yesterday suggested that fuel economy ratings could fall by 2 miles per gallon on the modified cars.

Plans for any resale of modified vehicles by VW must be separately approved.

CHECK OUT: 2012-2014 VW Passat TDI diesels approved for modification by EPA

Volkswagen, for its part, issued the following statement.

Volkswagen is pleased that it has received regulatory approval to offer affected customers in the United States an approved emissions modification (AEM) for approximately 326,000 Generation One 2.0L TDI vehicles with automatic and manual transmissions. This important milestone means that an approved emissions modification is now available for more than 98 percent of eligible 2.0L TDI vehicles in the United States.

Eligible customers will be notified that they can receive a modification free of charge at their preferred dealership if they want to keep their vehicles.

For all our stories on the lengthy and still-unfolding events around VW's diesel emission cheating globally, see our Volkswagen diesel scandal page.


Follow GreenCarReports on Facebook and Twitter.