* The engine is overheating. This is the most common reason for the engine fan to come on. The engine fan helps to cool the engine by drawing air through the radiator and over the engine block. If the engine is overheating, the fan will run at a higher speed to try to cool it down.
* The coolant level is low. If the coolant level is low, the engine will not be able to cool down properly, and the fan will come on to try to compensate. Check the coolant level and add more coolant if necessary.
* The thermostat is stuck closed. The thermostat controls the flow of coolant through the engine. If the thermostat is stuck closed, the coolant will not be able to circulate properly, and the engine will overheat. This will cause the fan to come on. Replace the thermostat if it is stuck closed.
* The fan switch is faulty. The fan switch is a temperature sensor that turns on the fan when the engine reaches a certain temperature. If the fan switch is faulty, it may turn on the fan even when the engine is not overheating. Replace the fan switch if it is faulty.
If you are not sure why your E55 AMG engine fan is on all the time, it is best to have it inspected by a qualified mechanic.
