Volkswagen's U.S. CEO, Michael Horn, spent several hours yesterday testifying in front of a Congressional panel on the company's growing TDI diesel-emission cheating scandal.

From that testimony, we can now break down how many cars and which models were affected, how the company expects to fix them, and when that process may start.

Senators were alternatively shocked, angry, and incredulous that the world's largest carmaker had deliberately installed software that bypassed emission controls when the car detected it was being operated on the open road.

DON'T MISS: VW Diesel Emissions Recall: What You Need To Know In 10 Questions

Horn apparently shared some of those feelings, exhibiting his own anger at his employer and agreeing with questioners that the affair was "very hard to believe."

As laid out in The Detroit News, here are the details of all affected models and how they'll likely be fixed, starting with those that can be addressed most quickly.

2015 Audi A3 TDI, New York City, Nov 2014

2015 Audi A3 TDI, New York City, Nov 2014

2015-2016 Golf TDI, Golf SportWagen TDI

2015-2016 Audi A3 TDI

2015-2016 Jetta TDI, Passat TDI, Beetle TDI

VW has suspended sales of all 2015 and 2016 cars with 2.0-liter TDI four-cylinder engines. But all 2015 and 2016 TDI four-cylinder models have a brand-new EA288 engine and will be the easiest to fix.

ALSO SEE: Why Did Volkswagen Cheat On Diesel Emissions In Its TDI Cars?

That's because they are fitted with a Selective Catalytic Reduction (SCR) exhaust aftertreatment system using urea injection, which will likely need only updated software to come into compliance with emission regulations.

Horn said Volkswagen expects to submit its proposed modifications for these cars to regulators for approval as early as next week.

  • HOW MANY CARS? 67,000
  • WHAT'S THE FIX? Updated software only
  • WHEN WILL IT START? Early in 2016
  • HOW WILL CAR CHANGE? Fuel economy will stay the same; performance may be "slightly affected"

2015 Volkswagen Passat TDI

2015 Volkswagen Passat TDI

2012-2014 Passat TDI

The company's Passat TDI mid-size sedans, built in Tennessee starting with the 2012 model year, were fitted with an older EA189 engine, but their emission-control systems included both a Lean NOx Trap and an SCR urea system.

U.S. CEO Horn said that those cars will need software updates, but may also require some hardware modifications, which he did not specify.

While he expects that owners of those cars could start to bring them in for modifications during the middle of next year, he did not specify a schedule on which VW would submit its proposed fixes for regulatory approval.

  • HOW MANY CARS? 90,000
  • WHAT'S THE FIX? Updated software and possible hardware modifications
  • WHEN WILL IT START? Mid-2016

2014 Volkswagen Beetle TDI

2014 Volkswagen Beetle TDI

2009-2014 Jetta TDI, Jetta SportWagen TDI

2010-2013 Golf TDI

2012-2014 Beetle TDI

2009-2013 Audi A3 TDI

These cars, which make up the bulk of Volkswagen's so-called "clean diesel" vehicles sold during model years 2009 through 2015, use the older EA189 engine but without the SCR urea-injection system.

The main new emission-control system--supposed to keep them compliant with new and more stringent limits on nitrogen oxides (NOx) that came into effect in 2008--was a Lean NOx Trap.

Other manufacturers have said privately they never understood how VW met the regulations with only that system; now we know it didn't.

This long list of vehicles will take the longest time to fix and require the most major hardware modifications. Horn said the company would also consider buying these cars back from their owners.

  • HOW MANY CARS? 325,000
  • WHAT'S THE FIX? Hardware modifications, perhaps including installation of SCR (urea injection) system, updated software; possible cash payments and/or buybacks
  • WHEN WILL IT START? Late in 2016

MORE: 2016 VW Diesel Lineup Withdrawn: Jetta, Passat, Golf, Beetle TDI Models May Be Modified

Many more details will have to emerge before the 482,000 owners of VW diesel cars with the "defeat device" software can know for sure how their cars will be modified and what effect that may have on performance and fuel economy.

We'll update this article as those details become available.

Meanwhile, Volkswagen stresses the cars are safe to drive and owners should continue doing just that.


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