Cutting its deadline extremely close, Volkswagen submitted a proposed fix for 3.0-liter V-6 TDI diesel models with "defeat device" software to U.S. regulators earlier this week.

With progress on addressing the 482,000 cars equipped with 2.0-liter four-cylinder engines still pending, the proposal for the 85,000 VW, Audi, and Porsche V-6 models gives the company a chance finally to start digging itself out of the diesel hole.

But officials of the California Air Resources Board (CARB) and the U.S. Environmental Protection Agency (EPA), must approve the plan before Volkswagen can proceed with a recall.

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VW just barely made a Tuesday deadline set by the California agency for submitting the diesel proposal, according to Reuters.

The plan covers various Audi luxury sedans and SUVs, as well as diesel versions of the Volkswagen Touareg and Porsche Cayenne SUVs, all of which were implicated in the cheating scandal several weeks after the EPA first revealed VW's use of "defeat device" software on its 2.0-liter TDI four-cylinder diesels.

Those 2.0-liter fours used software to ignore emission controls when in real-world use, according to admissions by VW's own engineers, the EPA said in September.

2015 Porsche Cayenne Diesel

2015 Porsche Cayenne Diesel

The situation is slightly different for the V-6 diesels, which proved to have three different Auxiliary Emission Control Device software routines that VW had not disclosed to the EPA as it was required to do before testing.

One of those three routines qualifies as a "defeat device" under somewhat arcane EPA definitions, but it's not clear whether the V-6 engines ignored emission-control routines in real-world use as the fours did.

The company initially denied that the 3.0-liter TDI models had "defeat device" software, but by early November it had issued stop-sale orders for all affected models.

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Both regulatory agencies acknowledged receiving the proposal for modifications last week, with CARB saying it would give the document a "thorough and complete review" to ensure it addresses all of officials' concerns.

The agency said it would decide on whether to approve the plan "in the near future."

As with a previously-rejected plan for the 2.0-liter four-cylinder TDI models, details of this plan were not made public.

2014 Volkswagen Touareg TDI

2014 Volkswagen Touareg TDI

But Audi and Porsche executives have indicated that the 3.0-liter V-6 models can be made to comply with emissions rules via simple software modifications, and possibly the fitting of new catalytic converters.

That would make the process easier than with the four-cylinder models, many of which may not be able to comply without the addition of expensive and complex Selective Catalytic Reduction (SCR) exhaust aftertreatment systems.

SCR systems inject urea fluid to convert the exhaust into less toxic emissions, and are already employed on the majority of diesel vehicles.

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VW's original proposal for modifying these cars was rejected by CARB and the EPA last month. Regulators said it lacked sufficient detail.

Meanwhile, Volkswagen is proceeding with a recall of some diesel models in Europe, where the relevant emissions standards are less strict.


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