coolant only lasts a few years before it needs changing because the freezing point of the liquid will be higher with time meaning its more likely to freeze during the winter causing ur engine block...
Need more info. Year, engine size and what it is in so I can answer your question correctly. You will have to ask your question again with this information and your problem. Failed oil cooler,...
the sensor could be dirty. clean off the accumulated crud with a toothbrush and if the low coolant light still remains on then the sensor will need to be replaced.