Two reasons. <br><br>Possibly the coolant tank is low, the sensor will set the light off when the coolant is low. Not only when it overheats. You have to pull the cover off the engine compartment and check the tank with the sensor and radiator cap on it. (not the one behind the license plate) If the light only flashes when its cold or cool, I would say that the tank is low and needs a top up. <br><br>Now, if you look at the overflow tank behind the license plate and the tank is full, but the main tank is low, chances are the radiator cap is bad. Because if the system is working properly, the overflow tank should be filling and refilling the system when the engine heats up and then cools off . As the engine heats up the coolant expands. When the pressure reaches 15lbs the pressure is relieved and excess coolant is bled off into the overflow tank. As the engine cools, the coolant contracts and created a vacumme and the cap opens the lets coolant back into the system. So if the main tank is low and the overflow is full, then the chances are the cap is not doing its job. <br><br> Another reason could be a bad sensor or bad relay up under the dash that controls the light. But since the light stops flashing, my thought is its simply low coolant.<br><br>PS: Unless you know the radiator cap has been replaced, its probably not a bad idea to replace it anyway.
