2013 Polo Vivo 1.6 overheating warning light

Hi all I’m hoping someone can help me with my car that keeps giving me the engine overheating warning light. The car was in a minor accident from behind and ever since then the warning light comes on if I go downhill. If I turn the engine on and off again it goes away till I go down a hill again. Car has it’s yearly services and radiator and all coolant devices has been checked. It does not happen any other time other than down steep hills. The temperature gauge remains constant and never over half way. Hopefull for some advice thanx in advanced.