Well my Check Engine light came back on and I went to the Dealer today and it was the DEF sensor again, they told me that the tolerance of the sensor was very narrow and that they had a new firmware for the 328d to hopefully fix the issue once and for all. We will see if the new firmware fixed the problem as we are expected to be at -30 degree Celcius tonight
Hope the light doesn't come back. I will keep everyone posted
Francis