Bosch declined to comment on the lawsuits or provide details about the way the engine software works, citing investigations by the authorities.

The Bosch software, also used by other carmakers, can be customized for different vehicles and motors. One question for the courts will be whether Bosch shares any blame because of the relative ease with which the software could be used as a “defeat device” to evade emissions tests.

Another question is why Volkswagen’s top managers never asked themselves why their engineers succeeded where others had failed in producing relatively inexpensive diesel cars that met American standards on nitrogen oxides, which are stricter than those in Europe.

“I was beating up on ’em pretty hard,” Mr. Lutz said. “They’re doing it and we can’t? Nobody could figure out how they were complying and their engine technology is very similar to everybody else’s.”

If Volkswagen is not able to fix the cars, there might be no alternative but to buy them back, a solution mentioned by the judge on Thursday. To get owners to surrender the cars, Volkswagen would probably have to pay more than the market value, adding to the already enormous financial burden from the scandal.

Mr. German, the owner of the 2010 Audi, who recently moved to Ithaca from Austin, Tex., said by phone that he would gladly accept the car at its prescandal book value, with perhaps a little extra to cover “the hassle factor.” According to Kelley Blue Book, an Audi A3 like Mr. German’s was worth about $16,300 before the emissions cheating became known and about $14,370 now.

“I don’t want my car anymore,” he said.