Why Does the Car Fan Keep Running? Thermistor Switch Failure and How to Check It

Does your radiator fan keep running even after you turn off the ignition? Or do you often hear the fan kicking in too frequently while driving? These symptoms may point to a faulty thermistor switch . In this post, we'll explore the reasons why the fan keeps spinning, the role of the thermistor switch, common failure signs, and how to troubleshoot the issue yourself.     1. What is a Thermistor Switch? A thermistor switch is a temperature-sensitive ON/OFF switch that activates the radiator fan when coolant temperature exceeds a certain level. In most vehicles, it’s mounted on the radiator, thermostat housing, or engine cylinder head. 2. Common Reasons the Fan Keeps Running Thermistor switch failure (stuck ON): Internal contacts stay closed, causing the fan to run even when not needed. Wiring short or relay malfunction: A stuck relay or shorted wire can also cause the fan to stay on continuously. ECU control error: In some models, the ECU co...