A cooling system for a secondary battery, the secondary battery being installed on an electric vehicle for driving the electric vehicle, the cooling system comprising: a cooling fan configured to send cooling air to the secondary battery, the cooling fan being configured to be driven based on a command value, the command value being a parameter that determines a rotational speed of the cooling fan; and a temperature sensor configured to detect a temperature of the secondary battery; the cooling system being characterized by further comprising: a controller configured to drive the cooling fan at a fixed command value for a predetermined period, when the temperature of the secondary battery becomes equal to or higher than a first predetermined temperature after the electric vehicle is started, the controller being configured to detect a presence or absence of an abnormality in the cooling fan based on an actual rotational speed of the cooling fan during the predetermined period, and the controller being configured to inhibit driving of the cooling fan at the fixed command value when the temperature of the secondary battery is equal to or higher than a second predetermined temperature that is higher than the first predetermined temperature, wherein, when a highest temperature of the secondary battery is higher than a predetermined value over a plurality of trips of the vehicle, the controller is configured to set the second predetermined temperature to a lower value as compared with a case where the highest temperature of the secondary battery is lower than or equal to the predetermined value over the plurality of trips of the vehicle. a cooling fan configured to send cooling air to the secondary battery, the cooling fan being configured to be driven based on a command value, the command value being a parameter that determines a rotational speed of the cooling fan; and a temperature sensor configured to detect a temperature of the secondary battery; the cooling system being characterized by further comprising: a controller configured to drive the cooling fan at a fixed command value for a predetermined period, when the temperature of the secondary battery becomes equal to or higher than a first predetermined temperature after the electric vehicle is started, the controller being configured to detect a presence or absence of an abnormality in the cooling fan based on an actual rotational speed of the cooling fan during the predetermined period, and the controller being configured to inhibit driving of the cooling fan at the fixed command value when the temperature of the secondary battery is equal to or higher than a second predetermined temperature that is higher than the first predetermined temperature, wherein, when a highest temperature of the secondary battery is higher than a predetermined value over a plurality of trips of the vehicle, the controller is configured to set the second predetermined temperature to a lower value as compared with a case where the highest temperature of the secondary battery is lower than or equal to the predetermined value over the plurality of trips of the vehicle. a controller configured to drive the cooling fan at a fixed command value for a predetermined period, when the temperature of the secondary battery becomes equal to or higher than a first predetermined temperature after the electric vehicle is started, the controller being configured to detect a presence or absence of an abnormality in the cooling fan based on an actual rotational speed of the cooling fan during the predetermined period, and the controller being configured to inhibit driving of the cooling fan at the fixed command value when the temperature of the secondary battery is equal to or higher than a second predetermined temperature that is higher than the first predetermined temperature, wherein, when a highest temperature of the secondary battery is higher than a predetermined value over a plurality of trips of the vehicle, the controller is configured to set the second predetermined temperature to a lower value as compared with a case where the highest temperature of the secondary battery is lower than or equal to the predetermined value over the plurality of trips of the vehicle.