It's imho not so clear cut whether this code is unethical or not. There is a legitimate argument that increasing NOx to reduce CO2 is better in the long term. Remember that the two are inversely related: the hotter and leaner your engine runs, the more NOx you produce, but your fuel efficiency also goes up.
In the long term, making their cars cause accidents that killed many people would reduce the environmental impact of humanity, so would also be arguably ethical by that logic.
