You do realize going to the dealer you put your wallet at their mercy?
Why not at the minimum get the info on your basics? Engine temperature for starter.
Expect them to start replacing sensors at $$$ a piece, chasing the problem. In the end - something as simple as thermostat.
Here's a thread about your P205b error
http://www.bimmerfest.com/forums/sho...ighlight=p205b