Volvo Repair: Cooling Fluid Indicator Light, volvo dealer, level sensor

Question
I have Volvo 1999 C70 HT. The dashboard cooling fluid indicator light is ON although the fluid level in the tank is just above the maximum.
I travelled more than 3k in city and highway.
I don't have any problems with engine overheating, yet for the last 2 months the light is steadily ON.
By visually, some dried coolant can be seen on outside of the tank but no other visual indications of leakage around the tank and hoses to radiator.
What might this indicate?
Thank you.

Answer
you have bad level sensor in coolant reservoir they go bad  if you from chicago i can install if for you for free  and if not than you have to go volvo dealer part is around $70 labor around $70 total $150 plus tax by volvo delaer to fix that problem  but you need to fix it if you have problem you cant tell if you low on coolant and you will damage the engine when you overheat  it .good luck