DETROIT — A Volkswagen engineer has pleaded guilty to one count of conspiracy in the company’s emissions cheating scandal, advancing a criminal investigation by agreeing to testify against others.

James Robert Liang, 62, of Newberry Park, Calif., entered the plea Friday in U.S. District Court in Detroit to one count of conspiracy to defraud the government through wire fraud.

Liang is the first person to enter a plea in the case, and his cooperation is a major breakthrough in the Justice Department’s probe into the scandal. Government documents say others were involved and point to multiple e-mails in German that likely came from VW employees in Wolfsburg, Germany.

Volkswagen has admitted to installing software on about 500,000 2-liter diesel engines in VW and Audi models in the U.S. that turned pollution controls on during government tests and turned them off while on the road.

The Environmental Protection Agency found that the cars emitted up to 40 times the legal limit for nitrogen oxide, which can cause human respiratory problems.

Liang, who began work for VW in 1983 in Germany, and also worked in the U.S., was indicted in June on one count of conspiracy to commit wire fraud and another count of violating the Clean Air Act. According to a plea agreement unsealed Friday, Liang admitted that he and others planned software known as a defeat device, that could cheat emissions tests after recognizing a diesel engine they were designing could not meet customer expectations and stricter emissions standards. Using the defeat device enabled VW to obtain a certificate from the Environmental Protection Agency needed to sell the cars in the U.S.

Liang will be sentenced on Jan. 11. The judge said that guidelines call for Liang to serve five years in prison. He also could be fined up to $250,000.