Mercedes-Benz S550 Radiator Fan Isn't Working

Diagnosing the Causes of a Non-Functional Radiator Fan in Your Mercedes-Benz S550 and How to Fix It

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Reviewed by
Bo Fader
Written by RepairPal Car Genius
Updated January 14, 2025
0%
34% chance it's the
Fan Motor or Clutch
0%
28% chance it's the
Fan Relay or Fuse
0%
23% chance it's the
Temp Sensor or Fan Control Module
0%
15% chance it's
Something else
The most common reasons a Mercedes-Benz S550 radiator fan isn't working are the fan assembly, the fan clutch, or the coolant temperature sensor.
  • Fan Motor or Clutch: A faulty fan motor or a malfunctioning fan clutch can result in inadequate cooling, causing the engine to overheat.
  • Fan Relay or Fuse: A faulty fan relay or blown fuse can prevent the cooling fan from operating, leading to engine overheating.
  • Temp Sensor or Fan Control Module: A faulty temperature sensor or fan control module can result in incorrect readings, causing the engine to overheat or the cooling fan to operate improperly.
Proper diagnosis will determine the exact cause of your symptom, saving you money on unnecessary repairs. The diagnostic experts at RepairPal Certified shops have the right tools and experience to solve any symptom.

How much does it cost to fix a Mercedes-Benz S550 radiator fan isn't working?

Common Repairs

The total repair cost will vary based on the condition of your vehicle and the number of repairs needed to fix your symptom. Proper diagnosis will save you money by finding the exact repairs needed to fix your car right the first time.

Over time serpentine belts stretch, crack, and the ribs that ride on the accessory pulleys being to wear smooth. A squealing noise that increases with engine speed or as engine driven accessories are turned on may be noted. The noise is caused by the belt slipping on the pulleys, insufficiently driving them. Ineffective air conditioning, a battery warning light, or intermittent power steering assist can result from this.

»MORE: Symptoms of a bad serpentine belt

The bad thermostat can cause two different sets of problems, depending on whether it's stuck open or stuck closed.

A thermostat that is stuck open can cause the engine to run colder than normal and turn on the check engine light. It may also cause poor fuel mileage and the heater to blow cool air.

A thermostat that is stuck closed will cause the vehicle to overheat. If a new thermostat doesn't resolve engine temperature problems, the cooling system needs to be checked for other issues.

» LEARN MORE: Signs of a bad thermostat, and how to fix it

When the engine coolant temperature sensor fails, it will send inaccurate information to the vehicle’s computer, causing the computer to react to false operating conditions. This will cause the engine to consume more fuel than normal, depleting fuel mileage, and causing black, sooty smoke from the engine under moderate to heavy acceleration. The check engine light will illuminate, and on-board diagnostic trouble codes may be stored for exhaust and emission system failure, fuel delivery system failure, and engine cooling system failure. Overheating may also occur, as the coolant sensor may be leaking fluid out of the engine, creating a an air pocket in the system.

When the radiator fans stop functioning properly, the engine temperature will rise. The spike in temperature will be highest when the vehicle is idling at a stop, but should subside once the vehicle begins moving again.

Additionally, the air conditioner typically won't blow as cold. This is because the air from the radiator fans also blows across the air conditioning condenser, so when the fans fail, both systems suffer.

You'll also usually see the check engine light and notice a drop in fuel economy. It's possible the fan will start making noise if it's failing, as well.

Troubleshooting Radiator Fan Issues in a Mercedes-Benz S550

When addressing radiator fan issues in your Mercedes-Benz S550, start with the simplest checks before moving on to more complex diagnostics. Begin by inspecting the fan relay and fuse, as these components are often the culprits behind fan malfunctions. If these are functioning correctly, proceed to examine the radiator fan motor or clutch for any signs of failure. It's also crucial to check the temperature sensor and fan control module, as these can impact the fan's operation. If your vehicle is overheating, ensure that the fan is engaging when the engine reaches higher temperatures. In cases where the heater fan is unresponsive, it may indicate a problem with the fan assembly or its controller. If you find that the fan assembly needs replacement, be prepared for a cost of around $250, excluding labor. By following this methodical approach, you can effectively diagnose and resolve radiator fan issues, ensuring your S550 runs smoothly.

What Are the Common Causes of a Non-Working Radiator Fan in a Mercedes-Benz S550?

When dealing with a non-working radiator fan in a Mercedes-Benz S550, it's essential to understand the common problems that could be at play. A faulty fan assembly is often the primary culprit, as wear and tear can lead to electrical failures or mechanical breakdowns. Additionally, the fan clutch, which regulates the fan's operation based on engine temperature, may also malfunction, preventing the fan from engaging when needed. Another critical component to consider is the coolant temperature sensor; if this sensor is defective, it may not signal the fan to turn on, resulting in inadequate cooling and potential engine overheating. By systematically checking these components, DIYers can effectively troubleshoot the issue and restore proper function to the radiator fan, ensuring the vehicle remains cool and operates efficiently.

Why is the Radiator Fan Not Working in a Mercedes-Benz S550?

When the radiator fan in your Mercedes-Benz S550 is not functioning, it is crucial to address the problem without delay. Ignoring this issue can lead to overheating, which may cause severe engine damage and costly repairs. The potential causes of a malfunctioning radiator fan, such as water ingress, damaged wiring, or blown fuses, highlight the need for immediate attention. If the fan is seized due to corrosion or if there are electrical faults, the engine may not cool properly, increasing the risk of overheating. Additionally, if the fan runs continuously or not at all, it could indicate a communication issue with the gearbox ECU, which requires professional diagnosis. By taking the time to investigate and resolve these issues, you can prevent further complications and ensure the longevity of your vehicle. Remember, timely intervention is key to maintaining your car's performance and safety.

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