James Robert Liang from Newbury Park, Calif., admitted to circumventing US emissions regulations for almost 10 years on behalf of his company, Volkswagen.
The 63-year-old was sentenced to 40 months in federal prison, with two years of supervised release for his part in the conspiracy -- alongside a fine of $200,000.
Over the course of nearly a decade, the engineer implemented software in thousands of so-called "clean diesel" vehicles sold by the German automaker in the United States which was designed to make the vehicles appear to adhere to the law in testing conditions.
However, these "defeat devices" only made sure pollution levels were acceptable in lab conditions, while reverted back to illegal levels of pollution whilst on the road.
In September last year, Liang admitted his guilt under a plea agreement to one count each of conspiracy to defraud the United States, to commit wire fraud, and to violate the Clean Air Act.
The engineer, employed by Volkswagen from 1983 to May 2008, was part of the team which worked on "EA 189" diesel engines. While developing the new engines, the team realized the designs would not be compatible with the US' new pollution laws, and so designed and implemented defeat devices to cheat environmental testing, all the while informing regulators that the new engines met emissions standards.
Liang and his colleagues falsely told both the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) that the engines met emissions standards, which in turn falsely assured customers that the vehicles they purchased were within legal pollution limits.
Others charged in the case are in Germany.
"As part of the certification process for each new model year, including model years 2009 through 2016, the co-conspirators continued to falsely and fraudulently certify to EPA and CARB that VW diesel vehicles met US emissions standards and complied with the Clean Air Act," US prosecutors said at the time of the plea.
According to prosecutors, US District Judge Sean Cox took into account his cooperation and his assistance in blowing Volkswagen's scandal wide open. While the engineer could have been sentenced to five years behind bars, the sentence was still more than his team requested as part of the plea agreement.
"Volkswagen continues to cooperate with investigations by the Department of Justice into the conduct of individuals. It would not be appropriate to discuss personnel matters."
Another Volkswagen employee is due for sentencing later this year. Oliver Schmidt has also admitted to conspiring to mislead US regulations and violate the Clean Air Act and faces up to seven years in prison. Schmidt once acted as a top emissions compliance executive.