The criminal case against Volkswagen, and the potential for a guilty plea, have set it apart from other recent auto industry investigations. In settlements with General Motors and Toyota over their handling of safety defects, for example, the companies agreed to pay large fines, but did not plead guilty.
Prosecutors are also mulling criminal charges against Takata, the Japanese manufacturer under criminal investigation for its defective airbags.
It is unclear whether prosecutors would also charge Volkswagen employees, but high-ranking Justice Department officials have forecast the possibility.
“We will follow the facts wherever they go, and we will determine whether to bring criminal charges against any companies or individual wrongdoers,” Sally Q. Yates, the United States deputy attorney general, said last year at a news conference.
American prosecutors have also traveled to Germany in recent months to interview Volkswagen executives, according to German prosecutors. In addition, the Justice Department has assured witnesses that they will not be arrested if they travel to the United States for questioning, according to a defense lawyer involved in the case as well as one witness, who spoke only on the condition of anonymity. German suspects cannot be arrested by the United States in their home country, which normally does not extradite its own citizens.
It is not clear if any of the suspects, who include former Volkswagen managers and engineers involved in diesel engine development, have accepted the offer. The offers typically allow witnesses to travel to the United States and back without fear of arrest, but do not include a guarantee they will not be charged in the future.
Volkswagen acknowledged in 2015 that it had fitted 11 million diesel cars worldwide with illegal software that made the vehicles capable of defeating pollution tests. The software enabled the cars to detect when they were being tested for emissions, and turn on pollution-control systems to curb emissions at the cost of engine performance. But those emissions controls were not fully deployed on the road, where cars spewed nitrogen oxide at up to 40 times the levels allowed under the Clean Air Act.
Volkswagen has already agreed to pay up to nearly $16 billion to resolve civil claims in what has become one of the United States’ largest consumer class-action settlements ever, involving half a million cars.
Under the settlement, most car owners have the option of either selling their vehicles back to Volkswagen, or getting them fixed, granted the automaker could propose a fix that satisfied regulators.
The Environmental Protection Agency and California Air Resources Board on Friday approved the first of those fixes, covering about 58,000 newer cars.
The scandal has affected a range of Volkswagen and Audi models, including the Audi A3, Volkswagen Beetle, Golf, Jetta and Passat diesel cars. It was brought to light in September 2015, when the Environmental Protection Agency accused Volkswagen of using software to detect when the cars were undergoing testing.
Along with the American and German investigators and prosecutors, the inquiry into the cheating has involved the law firm Jones Day, which was hired by Volkswagen to conduct an internal investigation.
The expected settlement was reported earlier by The Wall Street Journal.
Progress toward a resolution of the case has been frustrated by differences in German and American law and customs.
German prosecutors do not work out plea deals with suspects as routinely as prosecutors in the United States do. Punishments in the United States also tend to be harsher, and are seen as unacceptable by the German suspects.
One person has been convicted in the United States: James Liang, a former Volkswagen engineer who worked for the company in California.
Mr. Liang pleaded guilty in August to charges that included conspiracy to defraud the federal government and violating the Clean Air Act. He is expected to receive a reduced sentence in return for cooperating with investigators.