GMC Sierra 3500 Radiator Fan Isn't Working

Diagnosing the Causes of a Non-Functional Radiator Fan in Your GMC Sierra 3500 and How to Fix It

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Reviewed by
Andrew Hajjar
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 GMC Sierra 3500 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 GMC Sierra 3500 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 first indication of a defective fan clutch is a healthy cooling system that runs below or above the normal temperature range. This is due to the fan running too fast or too slow. Also, a seized cooling fan will cause a loud roaring fan noise from under the hood every time the accelerator is pressed, and the engine will feel as if it lacks power. In this situation it would be very difficult to turn the engine cooling fan by hand, of course when the vehicle is off. Finally, if the clutch fails the fan will either turn very slowly, and not respond well to engine speed.

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.

Troubleshooting Radiator Fan Issues in a GMC Sierra 3500

When troubleshooting radiator fan issues in your GMC Sierra 3500, start by inspecting the simplest components first. Begin with the fuse and wiring associated with the radiator fan; a blown fuse or damaged wiring can often be the root cause of the problem. If these elements are intact, move on to the fan assembly and fan clutch, as these parts can wear out or fail over time. Next, check the coolant temperature sensor, which plays a crucial role in signaling the fan to operate. If the fan still does not engage, delve into the electrical system, examining the fan relays and ensuring they are functioning correctly. The engine cooling fan system is controlled by the powertrain control module (PCM), so if all else fails, consider testing the relays and adding ground to the high and low-speed wires at the engine control module (ECM). By following this structured diagnostic approach, you can effectively identify and resolve radiator fan issues, ensuring your GMC Sierra 3500 runs smoothly.

What to Check When the Radiator Fan Isn't Working in a GMC Sierra 3500?

When troubleshooting a non-functioning radiator fan in a GMC Sierra 3500, it's essential to consider several common problems that could be at play. Start by examining the fan assembly itself, as physical damage or wear can prevent it from operating effectively. Next, inspect the fan clutch, which is crucial for engaging the fan when needed; a malfunction here can lead to inadequate cooling. The coolant temperature sensor is another vital component; if it fails, it may not signal the fan to turn on, resulting in overheating. Additionally, check the serpentine belts for signs of wear, as a compromised belt can hinder the fan's operation. The thermostat also plays a significant role in regulating engine temperature, and a faulty thermostat can disrupt the fan's functionality. Don't forget to inspect the cooling fan fuse for any damage, as a blown fuse can cut power to the fan. The cooling fan relay should also be tested, as a defective relay can prevent the fan from receiving the necessary electrical signal. Lastly, consider the blower motor, as issues here can also affect fan performance. By methodically checking these components, you can effectively diagnose and resolve the radiator fan issue in your GMC Sierra 3500, ensuring optimal engine cooling and performance.

Why is the Radiator Fan Not Working in a GMC Sierra 3500?

When the radiator fan in your GMC Sierra 3500 is not functioning, it is crucial to address the problem promptly to avoid serious consequences. A malfunctioning cooling fan can lead to engine overheating, which may cause extensive damage to engine components and result in costly repairs. Additionally, if the temperature gauge is not operating correctly due to fan issues, you may be unaware of rising temperatures until it’s too late. Other components, such as the water pump, thermostat, or temperature sensor, may also be implicated, and their failure can exacerbate the situation. Furthermore, if you notice a lack of airflow from the vents when using the heater or air conditioning, this could indicate a faulty blower motor, which can further complicate the cooling system's performance. Therefore, it is essential to troubleshoot these potential issues as soon as possible to ensure your vehicle operates safely and efficiently.

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GMC Sierra 3500 Radiator Fan Not Working: Causes & Solutions