At its core, a Cooling System Relay is an electrical switch that enables or disables the operation of cooling system components based on signals from temperature sensors or the engine control module (ECM). In most vehicles, the relay is used to control the electric cooling fan(s) that draw air through the radiator to cool the engine or to engage the coolant pumps that circulate coolant through the engine. The relay serves as a critical link in the temperature regulation chain, ensuring that the engine doesn’t overheat by automatically activating cooling components when necessary.