Volkswagen’s Dieselgate emissions-cheating scheme

At first glance, Volkswagen's "Clean Diesel" campaign looked like a major step toward making diesel cars cleaner, but the technology behind the vehicles turned out to work very differently under real driving conditions. Investigators found that software had been programmed to recognize when a vehicle was undergoing an official emissions test.

During those tests, the system could activate its full pollution controls, allowing the vehicles to meet regulatory standards. On ordinary roads, however, the vehicles could behave differently, producing far higher emissions than the testing results suggested. The software became known as a "defeat device."

The scale of the fallout was enormous. The scheme triggered regulatory investigations, lawsuits, recalls and major financial consequences, with early estimates putting the potential cost at roughly $18 billion. What makes the case stand out is that the deception wasn't hidden in the physical engine itself, it was built into the software controlling how the vehicles behaved.