Say the detection for the emissions testing is something like a flag in the software that says the car is on a dyno, or some other factors that the ECU has legitimate reasons to keep track of.<p>In that case, the defeat system is just a quick if else predicated on those state variables and swapping between a set of engine parameters that is emissions test safe and another set that provides better performance.<p>I don&#x27;t mean to insist that this must be the case, I&#x27;m just trying to illustrate that the cheat could happen at a level where much of the complexity has already been abstracted away.