BMW M4 Radiator Fan Relay Replacement Cost

The radiator fan relay is an electromagnetic device that switches the fan on and off when it receives a signal from a computer module in the vehicle.

Like many of the electrical components on a vehicle, the radiator fan (or cooling fan) requires 12 volts of power to operate. Since the fan is commanded by a small computer called the Engine Control Module (or the Powertrain Control Module) that emits a signal at a much lower voltage, a relay is tasked with actually switching the fan on and off. When the relay receives the command (by way of an electrical impulse in the control circuit) from the Engine Control Module, an electromagnetic field is created to move a switch inside the relay. That switch closes or connects the circuit for the radiator fan and turns it on. On older vehicles, the radiator fan relay is triggered by a thermostatically controlled sensor rather than by a computer.

The primary symptom of a bad radiator fan relay is an inoperative fan. But since most drivers are not paying attention to if and when the radiator fan is running, the symptom more likely to be noticed is an engine that is running hotter than normal or is overheating. A temperature gauge on the dashboard may read high or a warning lamp may come on. Engine coolant could be seen dripping underneath the vehicle or in the engine compartment, and steam could come from underneath the hood. A slight clicking sound coming from under the hood is not unusual when the relay kicks in normally, but if the sound is louder than normal, the relay might be failing.

A vehicle should not be driven if the engine cooling system is not in proper working order. An engine that overheats can become severely damaged if driven for very long. If the radiator fan relay is bad, the fan will not be able to assist in lowering the temperature of the engine coolant in the radiator and the engine will overheat, especially if the vehicle is left at idle. Have the vehicle inspected and repaired as soon as possible.