Initial optimism for the new WA 189 engine steadily diminished - at least internally. Early on, the company hoped to get as much as 60 miles per gallon, then 50 or more. By the time the diesels were ready for market in 2008, that figure had dropped to around 42, depending upon the model.
The problem was that the catalytic system meant to scrub smog-causing nitrogen oxides wasn't working as well as projected. An alternate approach, which would have injected a derivative of urea into the exhaust-cleaning process, was deemed too costly and only adopted across the board for the 2015 model-year.
The experts say that the "defeat device" apparently was introduced about this time to help address the performance issues.
Among the fixes VW engineers are likely to try would be to rewrite the basic engine software. But the experts warn that this approach could result in a loss of performance and reduced fuel economy.
An alternative might require the installation of new pollution control hardware, as well. That would be costly - and it's not even sure that approach would be practical or possible.
Some observers believe that Volkswagen might have to compensate owners for reduced performance and mileage, perhaps even offer a buyback program, as Fiat Chrysler recently announced in connection with defective Ram pickups.
VW insists it will do whatever it takes, the maker's new website declaring, "We are committed to making this right and preventing it from ever happening again. We will bring these TDI vehicles into compliance with the federal and state emissions regulations."
This spare-no-expense approach is one that turnaround strategists say is absolutely critical if the German maker is to ever rebuild its reputation.
VW should know.
Thirty years ago, it challenged consumers who were complaining about alleged safety problems with the Audi brand's big 5000 model. Ultimately, a federal investigation showed the carmaker was correct, but its seemingly arrogant approach so frustrated consumers that they didn't return to the brand. As a result, Audi almost abandoned the U.S. market.