The coolant temperature warning light is part of the engine cooling system. It illuminates red and indicates that the engine coolant is too hot, or that the coolant is low. If you see this light illuminate, stop driving as soon as possible and let the engine cool. Check the coolant level according to the recommended maintenance intervals in the owner's manual. If the level is OK, it may be necessary to replace the coolant in order to prevent further damage.
It may also be necessary to replace the thermostat, water temperature sensor, or coolant temp switch. If you are uncomfortable with this maintenance, consult a professional.
