I know it's rude to answer a question with a question but I'm a rude person.
Are you actually loosing coolant or is the light just staying on ??
If the coolant level stays normal but the light is on the float in the overflow tank might be stuck.
Open the cap (when the engine is cold) and move that little sucker up and down a few times and see what happens.
If you are indeed loosing coolant but cant see a leak that check your oil ASAP !
If it happened recently it might be because the temp drop and running your heater. The coolant starts flowing through the heater core and causes the level in the tank to drop. Same thing happened to me. Just add more coolant and keep an eye on it.
The heater valve is a big culprit for coolant leaks.
I have replaced two in 250K miles.
The dealer replaced the first one.
The second time I developed leaks I had the dealer look at it. They put a reserve tank on (sensor bad) and two radiator hoses and said it was fixed.
The next day the coolant light was on. I added coolant and let it run in driveway until it warmed. The heater valve leaked and it also showed a pin hole leak in the side tank of the radiator. I replaced the valve myself and put a epoxy patch on tank so I could find a radiator shop.
The Radiator shop tested with a pressure tester and the exopy patch leaked like a sieve! They put a OEM radiator in it $320 plus $80 labor.
First. Turn key to "on" so all the warning lights on the dash light.Check the "Coolant" light comes on and goes off with the rest of them. Wait a couple of minutes. Does "coolant" light come back on even though the engine isn't running? Yes? I expect you've already topped up the reservoir. there indeed is a float directly below the filler cap opening. Stick your finger in there and move the float collar down and up several times. Wait a couple of minutes. Does the light on the dash go out. No? Most likely the reed switch in the pillar of the level switch is fubared. Remove the retaining clip from the coolant reservoir next to the fender. Push the tank towards the motor untill it clears the retaining clips. Look under the tank. disconnect the wiring connector. Short out the two pins of the connector with fine wire, staple or what ever fits the pin holes. IF warning light goes out after a couple of minutes, the level switch is defective. Probably need to order a new tank or get a 'recycled' one. Good luck. Bye the way, my coolant light is on too. :bigroll: