Engineer: We can't make this engine pass NOx tests.
Ah, but that wasn't the situation. The engine could pass fine, which is what was happening when the software detected the test conditions. The problem is when running like that the engine didn't have as much power or fuel economy as when operating in dirty mode. This hack was to make the car more appealing to consumers by (in a virtual sense) selling one car to the public, and having the EPA test a different one. This was pure deceit.