Last November, the EPA announced that nearly 100,000 cars and SUVs fitted with VW Group's 3-liter V-6 diesel engines violated the Clean Air Act.

The agency said at the time that their emissions were up to nine times the legal limit in some circumstances.

While that's better than the figure of "up to 35 times" legal limits for some 2.0-liter 4-cylinder VW diesels, we now know the broad outlines of a buyback-or-fix agreement for those 2-liter cars.

CHECK OUT: VW 2.0-liter diesel agreement: what we know (and don't know) in 5 questions

Owners of the larger diesel vehicles remain in limbo, not knowing what kind of modifications would be required for their vehicles.

They include the TDI versions of the Audi A6, A7, and A8 luxury sedans and Q5 and Q7 crossover SUVs; the Volkswagen Touareg TDI utility vehicle; and the Porsche Cayenne Diesel SUV.

It appears, however, that an agreement between Volkswagen and the EPA may be near, according to a report yesterday by Bloomberg.

2015 Porsche Cayenne Diesel

2015 Porsche Cayenne Diesel

Talks between the two remain in progress and the situation is still "fluid," according to unnamed sources.

VW is now testing proposed updates to the V-6 diesel vehicles to ensure that they comply with emissions regulations under all circumstances.

According to Bloomberg, modifications to the vehicles might include not only software updates but installation of a new catalytic converter.

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All the V-6 diesel vehicles are fitted with a tank for urea solution, or Diesel Emission Fluid, as part of a Selective Catalytic Reduction aftertreatment system that converts nitrogen oxides into nitrogen, water, and carbon dioxide.

In theory, that should make modifications easier than in the bulk of the smaller diesels, which were sold without an SCR system installed.

The software in the V-6 diesels, according to the EPA, timed the EPA's emission test to the second—1,370 seconds—for use of a special "temperature conditioning" mode that helped the cars limit their emissions while being tested.

2014 Volkswagen Touareg TDI Sport with Navigation

2014 Volkswagen Touareg TDI Sport with Navigation

That mode was then switched off for real-world use, illegally increasing nitrogen oxide emissions past the maximum limits.

The costs of the affected vehicles when new ranged from roughly $40,000 to about double that, far higher than the prices of various Volkswagens fitted with the smaller diesels, which started in the low $20,000s.

It remains unclear when the EPA and VW might announce the outlines of an agreement to fix the 85,000 V-6 diesels.

DON'T MISS: How VW's 3-liter V-6 diesel cheat worked

The timing of a fix for the 85,000 V-6 diesel vehicles may depend on final terms being reached to modify or buy back the larger number of 2-liter 4-cylinder vehicles. Those terms are due June 21.

If that's the case, a resolution of the 2-liter TDI issues isn't due to be finalized by a California court until July 24, after public comments have been received on the June 21 plan.

But significantly for owners of the larger Audi, Porsche, and VW diesel vehicles, a buyback may not be included in the settlement for their cars.

Stay tuned for more.


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