Theoretically possible perhaps, but what incentive would "lone wolf" coders have for making the mechanical engineers look good? Even if the mechanical engineers who designed the engine and pollution control systems didn't know about the code changes, they should have had a good idea of what the approximate test results should have been, and if they were way better than expected it should have raised major red flags. Same goes for QA. Even if the change wasn't caught in a code review, the too-good-to-be-true results alone should have raised questions. I bet lots of people knew about this and either didn't want to risk their jobs by asking about it or were told "don't worry about it, it's a decision made above your pay grade". Unfortunately, we live in a world that demonizes whistle-blowers.