And then the onbord computer screen says servis engen soon emishion related fault. It also shoots out white smoke from the exost not constantly but when aselarating
Bad advice to take your car to an auto parts store with the expectation they will hook it up to their analyzer to diagnose your car's problem. They will NOT be able to give you an accurate reading because BMWs require highly specialized equipment for this. Your best bet is to take it into the service dept at a BMW dealership or to an independent BMW repair shop that has made the considerable investment in this type of equipment.
Many problems can cause the check engine light to come on. The white smoke from the exhaust may be due to a problem with the engine management system, or coolant leaking into the cylinders (the last problem would be very expensive to fix). It may or may not be related to the check engine light. Try going to an auto parts store which, for free, may hook your car up to an analyzer that can display the diagnostic codes. That would tell you why the light is coming on. Note: the comment in another answer to this question stating that only a mechanic with special equipment can detect engine faults on a BMW is wrong. Any scanner can read and display basic OBD II codes. A local Autozone did that for my 2004 745li for free, and stores of that kind can often find why the check engine light is on by doing so. BMW dealers and indie shops have equipment that reads the proprietary codes, but the expense of doing that may be unnecessary.
