What term describes the software used by Volkswagen to cheat emissions tests?

The software Volkswagen used to cheat emissions tests was called a defeat device. In the 2015 emissions scandal, the term referred to engine-management software designed to recognize when a vehicle was undergoing laboratory testing.

During an official test, affected diesel engines activated emissions controls strongly enough to meet regulatory limits. In normal road driving, the software reduced or altered that behavior, allowing the cars to deliver better performance and fuel economy while emitting far more nitrogen oxides than permitted. Investigators found emissions as much as 40 times the applicable limit in some real-world conditions.

The scandal involved Volkswagen Group’s turbocharged direct-injection diesel engines, especially the EA 189 family. The company said about 11 million vehicles worldwide were affected, including roughly 500,000 in the United States. The U.S. Environmental Protection Agency issued its notice of violation on September 18, 2015.

“Clean diesel” was Volkswagen’s marketing language, not the name of the cheating software. “Cheat chip” and “emission killer” are informal distractors, whereas “defeat device” is the established regulatory and legal term.