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this usually occurs when the engine coolant temperature sensor is faulty or disconnected
the ECU will put the fans on all the time as a failsafe condition
so I'd 1st locate the temp sensor on the engine that should be close to the top hose entry point and check over the sensor connection for corroded contacts and damaged wiring
if it looks OK then I'd consider replacing the sensor
it would also be worthwhile checking the condition of the fan relay in the underhood fusebox as it may be stuck on
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