On Tuesday, Volkswagen said 11 million of its vehicles worldwide contained the so-called "defeat device," software that allowed the cars to beat the testers. Its revelation was a stunning increase from the 482,000 cars previously identified by the EPA.
Winterkorn said he was "endlessly sorry" and asked in a video message for "your trust on our way forward." However, that did little to douse speculation about his future.
VW has yet to explain who installed the software, under what direction, why and who knew about it. Winterkorn said Tuesday that he didn't have all the answers himself at the time, but also that it would be wrong to cast doubt on the whole workforce "because of the grave mistakes of a few."
The deputy leader of Germany's IG Metall industrial union, Joerg Hofmann, cautioned against premature personnel decisions and said that "all the facts must be on the table first." He told news agency dpa he hopes "that diesel technology as a whole will not be damaged."
On Tuesday, New York Attorney General Eric. T. Schneiderman said he had opened an investigation into the Volkswagen cars and would collaborate with other states to enforce consumer and environmental protections in the case.
Volkswagen has set aside an initial 6.5 billion euros ($7.3 billion) to cover the fallout and "win back the trust" of customers, though it didn't mention possible fines.
Beyond legal issues, the scandal is a huge problem for a brand long identified with trustworthiness and reliability. And there are concerns that could spill over into a wider image problem for goods "made in Germany."
The head of the German exporters' association, Anton Boerner, urged Volkswagen to put the facts on the table quickly. "Whether collateral damage arises for the image of German products also depends on that," he told Germany's Bild daily.
He added, however, that the good image of German goods "is rooted in excellent products from thousands of companies and, thank God, does not depend on a single company. We should keep a sense of proportion here."
However, Carsten Brzeski, chief economist at ING Germany, said the ongoing refugee crisis and now the "Volkswagen shocker" pose new risks to the German economy.
Brzeski conceded that it's "unclear" what the impact of the VW crisis will be, but that there will likely be one given the size of VW. It is, he notes, "one of Germany's most important global champions" and an "important growth driver for the German economy." In the second quarter, German GDP grew by a quarterly rate of 0.4 percent.
"While the German economy defied Greece, the euro crisis and the Chinese slowdown, it could now be facing the biggest downside risk in a long while," Brzeski said.
Another question arising from the scandal is whether Volkswagen was alone in looking to dupe the testers. Worries that other carmakers may have indulged in similar malpractices have hit the share prices of many other auto makers in Europe, though not on the scale of VW.
On Wednesday, other European carmakers saw their share prices fall sharply then recoup some lost ground. In midday trading, BMW's share price was up 0.5 percent, while Daimler's rose 0.8 percent. French carmakers Peugeot Citroen and Renault fared worse though, with both seeing 2.6 percent declines.
"Dealers despise being kept in the dark, and the carmakers as a whole will be a sector to swerve until there is a conclusion to this saga," said David Madden, market analyst at IG.
The problems afflicting German carmakers prompted the country's biggest bank, Deutsche Bank, to revise down its view on the main German stock market.
In a note to clients, the bank lowerd its forecast for the DAX because carmakers account for 25 percent of its total value. It warned of "a potentially more sustained loss in brand value and prolonged recovery period ahead in the U.S."