Eather take it to a dealer, princeton, circle, or desemoe which ever is closest. Other then the dealers I dont know of any shops that specificaly deal with BMW or german cars. There are a few but there near Trenton.
But correct me if Im wrong but how does the check engine light come on if the thermo is open. Is there a sensor on the housing or soemthing I really dont know. Other then that how many miles are on your car? beucase it could be the o2 sensor if your car has over 100k on it. My light comes on when Im idling sometimes. And I just crossed over 100k