VW brand boss Herbert Diess again apologized for the diesel scandal on Tuesday in Las Vegas.

Increasingly desperate to find an acceptable fix for the diesel emissions scandal impacting about 500,000 vehicles sold in the United States, Volkswagen may be forced to buy back more than 100,000 of those cars, according to a news report from Germany.

Many of the others might face extensive mechanical updates that would be complex, costly and slow to complete, according to a report in the Sueddeustsche Zeitung. But Herbert Diess, the CEO of the Volkswagen brand told TheDetroitBureau.com this week that some of the most recent models might require only a “fix with the software.”

One way or the other, “Our most important task in 2016 is to solve the diesel issue in the U.S.,” said the executive, following a keynote presentation at the Consumer Electronics Show in Las Vegas.

In September, the U.S. Environmental Protection Agency announced it had discovered VW was using a so-called “defeat device” capable of determining when a vehicle equipped with the maker’s 2.0-liter turbodiesel was undergoing emissions tests. In such a case, it was capable of meeting strict U.S. standards for the production of oxides of nitrogen, or NOx, otherwise it would far exceed the mandate.

The maker quickly confirmed the discovery, and then acknowledged a subsequent EPA charge it had cheated on tests involving its 3.0-liter diesel, as well.

(VW’s Diess says he’s focused on fixing diesel problem, not the costs of doing so. For more, Click Here.)

VW is launching repairs in other markets, including Germany, this month for nearly 11 million of its vehicles also equipped with the rogue software. But because the U.S. – as well as California, with its own emissions rules – are significantly tougher on NOx, the company’s engineers have yet to find an acceptable solution here. That prompted the U.S. Justice Department to file a civil lawsuit this week against the German maker.

The loss of diesel models, like the Golf TDI, had a particularly harsh impact on VW sales in the U.S.

“Car manufacturers that fail to properly certify their cars and that defeat emission control systems breach the public trust, endanger public health and disadvantage competitors,” said Assistant Attorney General John C. Cruden for the Justice Department’s Environment and Natural Resources Division.

(For more on the Justice Dept. lawsuit, Click Here.)

A part of the problem appears to be the fact that VW actually produced three different versions of the 2.0-liter diesel engine during the seven years leading up to last year’s revelation. While the newest version very well may be fixable simply by revising the code controlling the engine, older models aren’t so easy to bring into compliance.

The Sueddeustsche Zeitung citing unnamed sources, indicates those other vehicle could require major hardware retrofits. Not only would that be expensive, but it could require owners to leave their vehicles at Volkswagen service departments for an extensive period.

Complicating matters, even though VW might think it can fix things with the hardware updates, it has to prove to federal regulators, as well as those from the California Air Resources Board, that any revisions will be able to maintain legal emissions levels for an extensive period, as required by law,

In some cases, it appears, VW may opt to simply get older models – involving about 115,000 vehicles – off the road entirely. That, the German paper indicated – could mean buying them back or offering owners a favorable deal on a trade-in.

VW is under increasing pressure to find an acceptable solution. The federal lawsuit could subject it to an estimated $18 billion in fines for the 2.0-liter diesel subterfuge alone under the Clean Air Act. The maker would likely be able to negotiate that down substantially if it is seen to be cooperating with the government, however, and a Goldman Sachs report estimates the final figure will be closer to $500 million.

That doesn’t include the cost of the fix itself, nor the likely cost of settling the more than 450 lawsuits that have so far been filed against the company. Most of those will now be consolidated and heard in federal court in San Francisco.

Separately, the Sueddeustsche Zeitung reported that about 50 employees, including some senior managers, have acknowledged their role in the diesel cheating as part of a VW amnesty program. That appears to torpedo the maker’s earlier claims that only a small handful of engineers were responsible for the cheating.

The U.S. Justice Dept., as well as prosecutors in Germany, could yet bring separate criminal charges against some of those employees.

(VW unveils electric BUDD-e microbus concept. Click Here to check it out.)

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