A veteran Volkswagen engineer pleaded guilty today to helping the company cheat on federal air-pollution tests as a result of a Justice Department investigation. James Liang appeared in U.S. District Court in Detroit this morning pledged to cooperate with prosecutors in hopes of seeking a lighter sentence. He faces up to 5 years in prison and fines of $250,000 or more. Volkswagen reached a civil settlement earlier this summer with regulators and the State of California that requires the automaker to pay $16.5 billion to owners.