2003 x5 3.0 with this problem.
Crankcase ventilator froze and white smoke is exhaust. In my case it routed back into the cabin ventilation system.
Fried both catalytic converters. Vehicle cabin stank of fumes for weeks.
Quoted $8800 fix.
BMW advised me that I should not drive my vehicle on short trip when temperature is below 0.
I live in Canada.
As you might imagine I was quite taken aback by this response.
I worked my way up through the chain at BMW Canada, was told that the crankcase ventilator was not part of the power train so was not covered.
I was once threatened by BMW Canada that they would now charge me the entire amount if I did not stop my inquires. I even had a BMW representative in Canada tell me "He was BMW and to stop."
I was able to get BMW Canada to assume responsibility of both catalytic converters and reduced fix to $2300 CAN.
I had had vehicle serviced as per manufacturers guidelines.
BMW installed "covers" to protect the crankcase ventilators.
I inquired if there were checked as part of routine maintainance; No.
I inquired if the crankcase ventilators were heated electrically or pneumatically; No.
I rebutted that this is a design flaw for a vehicle built to be driven in Canada where it is below 0'C 1/2 the year.
I pursued this though Transport Canada Passenger Vehicle Division and was advised that this was/is a known problem to BMW, for example, the issued a Tech Safety Bulletin about this particular issue; however, no recall and dealers and BMW is not legally obliged to inform you of this short coming. Apparently simply issuing the TSA covers them.
There is still an ongoing investigation within Transport as the Inspector that contacted me informed me there were major issues in Minnesota, Alberta, Ontario and North Dakota.