It was only three weeks ago that Volkswagen headquarters in Germany came out swinging against the U.S. Environmental Protection Agency.

The EPA had issued a complaint in which it accused VW of incorporating emission-cheating software into its 3.0-liter V-6 TDI diesels, used by Audi and Porsche as well.

But it appears the company's tone has changed since then.

ALSO SEE: VW In Germany Denies EPA V-6 Diesel Charges, Porsche Pulls Cars Off Sale

Last Friday, the company met with regulators from the EPA and the California Air Resources Board, and told them that the emissions problems with its 3.0-liter V-6 diesel engines extended to 75,000 more vehicles than it had first acknowledged, according to Reuters.

That means that every single Audi, Porsche, or Volkswagen sold in the U.S. with that engine since 2009 has the problematic software, boosting the total from 10,000 to 85,000 vehicles.

2014 Volkswagen Touareg TDI

2014 Volkswagen Touareg TDI

Then, yesterday, Audi's German headquarters issued a statement saying that it will "revise, document in detail, and resubmit for U.S. approval" parts of the software that controls the operation of the engine and its emission-control system.

The issues center around what are defined in agency rules as Auxiliary Emission-Control Devices (or AECDs) that temporarily allow the engine to exceed emission limits solely when required to protect the emission system from damage under specific operating conditions.

DON'T MISS: VW Diesel Software Cheats On European Emission Limits Too, BBC Test Shows

For instance, starting a cold TDI engine and then immediately flooring the accelerator for 60 or 90 seconds--before catalytic converters in the emission aftertreatment system have fully warmed up--might require bypassing those systems for a short period of time.

The EPA allows these software routines, but they must be fully disclosed--and their operating parameters specified--during the car's initial emission certification.

Note that AECDs, which are legal if disclosed, differ from the "defeat device" software in VW's 2.0-liter TDI four-cylinder diesels, which kept emissions within legal limits only when it detected that the cars were undergoing emission testing.

2015 Porsche Cayenne Diesel

2015 Porsche Cayenne Diesel

VW has said that "defeat" software is included in roughly 11 million vehicles fitted with the diesel fours since 2009, and sold worldwide.

Volkswagen and Audi cars fitted with those engines violate U.S. emission limits in real-world use--and yesterday, a BBC investigation showed that the software similarly let them violate European standards as well.

Audi said in its statement on the larger V-6 diesels that three separate AECD software routines had not been properly disclosed to the EPA.

MORE: VW To Recall 8.5 Million TDI Diesel Vehicles Across Europe; Fixes Not Yet Revealed

It will update its V-6 TDI software, it said, and resubmit the cars for certification. If approved, all existing V-6 TDI cars will likely be recalled to have their software updated.

Two of the AECDs prevent deposits on the metering valve for urea liquid, and prevent poisoning the catalyst in the Selective Catalytic Reduction system with hydrocarbons from unburnt fuel.

The third AECD "relates to the temperature conditioning of the exhaust‑gas cleaning system," Audi said. But U.S. regulations define that function as an illegal "defeat device," which is a more dire problem than undisclosed AECDs.

Audi Q7 e-Tron 3.0 TDI Quattro (European model), Madrid, Nov 2015

Audi Q7 e-Tron 3.0 TDI Quattro (European model), Madrid, Nov 2015

Audi is "committed to continue cooperating transparently and fully," the statement said, with a goal of "finding quick, uncomplicated and customer-friendly solutions" to make the cars legal again. 

The company underscored that all its diesel vehicles remain "safe and roadworthy."

However, the stop-sale order on all VW Group vehicles in the U.S. that have been fitted with that engine will continue until further notice, it said. They are the following models:

  • Audi A6 TDI: 2014-2016
  • Audi A7 TDI: 2014-2016
  • Audi A8 TDI: 2014-2016
  • Audi Q5 TDI: 2014-2016
  • Audi Q7 TDI: 2009-2016
  • Porsche Cayenne Diesel: 2014-2016
  • Volkswagen Touareg TDI: 2009-2016


Follow GreenCarReports on Facebook and Twitter.