A control method for a cooling system is provided. The method includes determining whether the output signals of a first coolant temperature sensor and a second coolant temperature sensor satisfy a predetermined coolant overheating condition. A coolant control valve unit is operated to move the cam to a maximum position when the predetermined coolant overheating condition is satisfied. Additionally, a control temperature is determined according to an output signal of the first coolant temperature sensor and the second coolant temperature sensor and an operation of the injector is limited according to the determined control temperature.