Why would the service engine soon light go on three separate times in new car?

What is your question?

I have a new 135i purchased in Germany and U.S. specs. I have taken it three times to the German BMW dealer and they keep replacing "sensors." They continuously make excuses that "the air quality must be bad" or other similar excuses -- What would be the reason -- there are only 2000 miles on my car and the first light came on at 300 miles....I'm fed up -- I don't have time to waste taking my car to the shop every time the light goes on