+1 on the sensor.
The sensor is located in the bottom of the coolant reservoir. I do not believe that the sensor itself is replaceable,but I could be mistaken about this. If the reservoir has signs of rust,or other debris,try flushing it out. I'd also try adding coolant, because a light that is going on and off would indicate the sensor is functioning,and the coolant is low. More so if the light comes on during turns when the coolant would move away from the bottom of the tank.
I've noticed that although the reservoir on these cars appear to have sufficient coolant,the level is actually low. I've added as much as a quart of coolant to a reservoir that at first look seemed to have sufficient coolant in it.