Well it is quite easy actually. Your biggest customer request a bunch of features, some for test purposes. You find something fishy, you ask your boss and he te

Well it is quite easy actually. Your biggest customer request a bunch of features, some for test purposes. You find something fishy, you ask your boss and he tells you orally to just do it because this customer is the most important, or he takes the matter seriously and gives the feature directly to your colleague in India who doesn't raise an eyebrow. The SW is done and millions of vehicles have the feature. Don't count on other engineer to spot the cheat because everyone has a specific area of expertise, and the software is closely related to the engine hardware. It is very difficult to understand the purpose of each piece of code. Remember that at that time, noone was ever tried for cheating the exhaust norms and the compliance team only cared about financial fraud.