Prosecutors say that Liang was aware that the German carmaker was using software to cheat on emission tests on almost 600,000 diesel vehicles.
A Volkswagen engineer who had a key role in the company's diesel emissions scandal has been sentenced to more than three years in prison and fined $200,000.
James Robert Liang, 63, knew the German automaker was cheating and worked to cover it up, U.S. District Court Judge Sean Cox said during the sentencing hearing in Detroit.
"There is no legitimate sentencing objective served by exposing Mr. Liang, a 63 year-old man who weighs 120 pounds, to threats to his physical safety, or the extortion demands he may face in a low-security prison", Nixon wrote in a court filing.
"When Liang and his co-conspirators realized that they could not design a diesel engine that would meet the stricter USA emissions standards, they designed and implemented software to recognize whether a vehicle was undergoing standard United States emissions testing on a dynamometer, versus being driven on the road under normal driving conditions", the release stated on Friday.
Mr. Liang, a German national, has agreed to be removed from the US following his prison term, according to prosecutors. The California resident should serve any sentence under house arrest or at a less unsafe jail in the Los Angeles area, defense lawyer Daniel Nixon said. "He was not motivated by greed".
Liang's lawyer had urged the judge to consider a lighter penalty in recognition of his assistance with other cases.
According to court records, from 1983 until May 2008, Liang was an employee of VW, working in its diesel development department in Wolfsburg, Germany. Earlier this month, Oliver Schmidt, 48, a former manager of a VW engineering office in suburban Detroit, pleaded guilty to conspiracy and fraud charges related to the scandal. He is scheduled to be sentenced December 6.
The company also agreed to $1.2 billion deal that covered fixes and buy backs of 78,000 additional 3-liter cars.
The US investigation has led to charges against seven others in the US and sparked probes in other countries.
Mr. Liang "was instrumental in calibrating the vehicles" so they would fully engage pollution controls during laboratory emissions tests and then reduce their effectiveness on the road to allow nitrogen oxide to be released from tailpipes at over 30 times the legal limit, according to prosecutors.