Prawdopodobnie jest to czujnik poziomu plynu chlodniczego
Mozna to wymienic samodzielnie bez spuszczania plynu.
Opis po angielsku:
"If the coolant level is fine it could be the sensor in the bottom of the tank. Good news: the replacement sensor is about $20 from the dealer.
Even more good news: you can replace it without draining the system - it screws into a cavity in the bottom of the coolant expansion tank. R&R is about 15 minutes.
Typically, after years of vibration (the sensor isn't in the coolant) the electrical insulation on the switch itself fails."
Przestudiuj schemat ponizej. Sensor oznaczony jest numerem 5.
http://www.realoem.com/bmw/showparts.do?model=BM33&mospid=47709&btnr=17_0140&hg=17&fg=05
Instrukcja do wymiany sensora po angielsku:
"Do it from underneath the car. Pull off the front undercarriage panel. Looking up at the bottom of the expansion tank, the sensor will be white/grey color. Unclip the harness and pull it off the sensor. Then turn the sensor counterclockwise to loosen and remove by pulling it straight out. Some coolant might spill out, don't know because I had already drained the tank before removing it"
Jesli to nie pomoze to prawdopodobnie trzeba wymienic zbiornik oznaczony na schemacie numerem 3.
Cala dyskusje na ten temat znalazlem na
http://forum.e46fanatics.com/showthread.php?t=501630
Pewnie sa tez konkretne poradniki DIY na sieci. Mozesz tez sprawdzic w TIS (poszukaj na torrentach albo emule) ale ja znalazlem tam tylko instrukcje spuszczania i napelniania plynu z ukladu chlodniczego.