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My Cooling Fan Won't Stop Running on My Radiator

Updated July 19, 2017

Your cooling fan operates through a series of circuits. The computer turns the cooling fan on and off when it receives a temperature indication from the coolant temperature sensor. When the temperature exceeds a specific value -- usually 102 degrees Celsius -- the computer will turn the fan on. The operating components in the cooling fan circuit include the cooling fan fuse, relay, coolant temperature sensor and the computer. Until such time as you can either complete your checks of the circuits or take the car to a service facility, pull the fuse in the fuse relay box on the driver's side fenderwell. The fan will discharge the battery quickly if left running.

Open the bonnet and locate the fuse relay box on the driver's fenderwell. Remove the lid.

Look on the inside of the lid and for the mapping of the fuses and relays with their location. Pull the cooling fan relay out of the box.

Replace the cooling fan relay with a new one. A stuck closed relay is the only thing that can operate the cooling fan continuously with the key off. The computer looses power with the key off and the same applies to the coolant temperature sensor. The relay, however, has direct power to one side, the same as a light switch. The computer sends power to the relay to activate it and turn the fan on. Once activated, however, if the relay sticks in the closed position then the fan will run until the battery is totally discharged.

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About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).