BMW Repair: BMW E46 coolant level sensor, bmw e46, coolant level

Question
2000 e46 323i wagon, 70K miles. Just replaced a ruptured coolant expansion tank, bleed the air out correctly. Eveything is normal, except the coolant level light is ON after one minute engine running. The level sensor/light was working before tank replacement. I even use a rubber band to hold the tank level stick up high for simulation test, but the light is still turn on. How does this non-contact level sensor work? Is there a magnet attached to the level stick? is my new tank's level component bad?

Answer
Sometimes the sensor gets damaged when removeing and re instaling sensor in new expansion tank, inside the tank there is a float that has a magnetic ring, the sensor when installed senses where the magnetic ring is, high or low. check the sensor or check the connection. allso when you bleed the system have the heater on so that the heater core fills up.   hope this helps......Thanks Nathan babbitt  (Babbitt Motor Werks)... And yes i have seen the new tank with a bad float