Cooling Fan Not Working? Common Causes

If an engine stays at a normal temperature while driving but starts to run hot in traffic, the cooling fan system is one of the first areas to investigate. At road speed, air passes naturally through the radiator. At low speed or while stationary, the electric fan has to provide that airflow.

How the cooling fan is controlled

Modern vehicles may use one or more electric fans controlled by the engine ECU, a separate fan module, relays or a variable-speed controller. The ECU decides when to run the fan using coolant temperature, air-conditioning demand and other operating data.

Common fan faults

Possible causes include a failed fan motor, blown fuse, damaged relay, wiring fault, failed control module or poor power and ground supply. Some fans can work during an actuator test but still fail during normal operation if the ECU is receiving incorrect temperature information.

Temperature sensor faults

If a coolant-temperature sensor or radiator-outlet sensor reports an unrealistic value, the control system may not request the fan correctly. Looking at live data and comparing sensor readings as the engine warms up can be more useful than replacing the fan immediately.

Thermostat and coolant circulation

A fan that does not run is not the only reason a vehicle can overheat. A stuck thermostat, weak water pump, trapped air, restricted radiator or low coolant level can create similar symptoms. The complete cooling system should be assessed rather than focusing on one component.

Do not keep testing an overheating engine

Repeatedly allowing the temperature to climb too high can damage the cylinder head, head gasket and other engine components. If the temperature continues rising, switch the engine off and investigate the cause rather than waiting for the fan to eventually start.

Capital Garage provides cooling-system diagnosis and repairs in Ruislip. See our cooling system repair service or book online.