Auxiliary Fan Control Unit Buyer's Guide
- Control modules are computers that operate a variety of components and systems from the powertrain to the suspension system and climate control.
- Many electric cooling fan circuits include a temperature sensor, a relay, a control unit/module, and a fan motor.
- The auxiliary fan control unit is a control module that controls the speed and operation of an auxiliary fan.
- The fan’s control unit may use the input from different sensors (engine coolant temperature sensor, ambient air temperature sensor, vehicle speed sensors, etc.) to determine when the auxiliary fan needs to be turned on. When extra cooling power is needed, the auxiliary fan control unit turns the auxiliary fan on to cool the engine.
- In vehicles with variable fan speeds, the PCM or the auxiliary fan control unit generates a signal for the fan motor which causes the fan to run faster or slower.
- Auxiliary fan control unit failure is a relatively uncommon cause of auxiliary fan malfunction. In fact, the most common problem with the auxiliary fan is a faulty fan relay.
- If you suspect that there is a problem with your auxiliary fan control unit, you should conduct a thorough diagnosis. Make sure to rule out the most likely causes for the issue first before testing the least likely ones.
- The price of aftermarket auxiliary fan control unit replacements range from $23 to $413.
An engine’s cooling system’s efficiency is determined by the effectivity of its design and its individual components. The engine’s heat output, the vehicle’s radiator size, and the type of fans to be used are all factored in during the designing process. The engine cooling system is important because it maintains the engine’s operating temperature and prevents the engine from overheating.
Many modern engines are equipped with electric cooling fans. For some engines, the stock electric cooling fan is enough to regulate its temperature. However, some engines may require additional cooling power in the form of an auxiliary fan.
The vehicle’s powertrain control module (PCM) typically controls the auxiliary fan’s operation. However, a dedicated fan control unit/module is used in some cases. What is this part and when should you check if you need a replacement? This guide will answer these questions and more.
What is an Auxiliary Fan Control Unit?
Modern vehicles are more advanced and computerized than older vehicles in that they rely on a network of sensors, control modules, and other components to maximize their efficiency and automate most of their operations. Control modules are computers that operate a variety of components and systems from the powertrain to the suspension system and climate control. For example, the PCM is a major control module that controls engine functions and sometimes even the transmission.
The auxiliary fan control unit is a control module that controls the speed and operation of an auxiliary fan.
What is an Auxiliary Fan?
An auxiliary cooling fan is a supplemental electric fan that’s installed to provide additional engine cooling ability on top of what the belt-driven fan provides. If the primary fan falters, the auxiliary fan can pick up the slack.
This fan is typically installed in vehicles that tow heavy loads or drive under conditions that strain the engine, such as driving uphill. Auxiliary fans also keep the engine cool when the vehicle is stuck in traffic or when it travels at low speeds.
An auxiliary fan is often placed in front of the radiator. However, the configuration of components under the hood varies, depending on the vehicle manufacturer. That’s why the location of the auxiliary fan isn’t absolute.
How does the Auxiliary Fan Control Unit work?
Many electric cooling fan circuits include a temperature sensor, a relay, a control unit/module, and a fan motor. The PCM or the fan’s control unit may use the input from different sensors (engine coolant temperature sensor, ambient air temperature sensor, vehicle speed sensors, etc.) to determine when the auxiliary fan needs to be turned on. When extra cooling power is needed, the auxiliary fan control unit turns the auxiliary fan on to cool the engine.
Extra cooling power isn’t needed when the engine is first started. That’s why in many cases, the fan isn’t switched on until the engine reaches its operating temperature. Once the engine reaches that temperature, the auxiliary fan may cycle on and off and run at idle or low speed to maintain the engine’s normal operating temperature.
Auxiliary fans, in some vehicles, can change speed so it can adjust its cooling effect as needed. In fact, some fans have low, medium, and high-speed settings, while others have additional speeds. In vehicles with variable fan speeds, the PCM or the auxiliary fan control unit generates a signal for the fan motor which causes the fan to run faster or slower.
To save energy, electric cooling fans are turned off whenever the vehicle reaches or exceeds a certain speed (35 mph or 55 kph, in some cases). At this point, the vehicle’s speed alone is able to cool the radiator down. However, if the fan’s control circuit detects that the engine temperature is still too high, it will turn on the auxiliary fan to cool the engine and to avoid engine damage.
When to Replace Your Auxiliary Fan Control Unit
Auxiliary fan control unit failure is a relatively uncommon cause of auxiliary fan malfunction. In fact, the most common problem with the auxiliary fan is a faulty fan relay. When the fan relay malfunctions, the auxiliary fan may not be able to cool the engine enough to prevent overheating. You may encounter other problems with your auxiliary fan or the rest of your auxiliary fan assembly. Listed below are the most common causes of auxiliary engine cooling fan failure:
- Faulty temperature sensor/switch
- Faulty engine thermostat
- Fan relay issues
- Wiring problems
- Faulty fan motor
Auxiliary Fan Control Units and Diagnostic Trouble Codes
As mentioned above, modern vehicles are equipped with sensors and computers that monitor a vehicle’s performance. When a sensor’s input does not match the expected values, the vehicle’s computer stores the error as a diagnostic trouble code. The engine’s computer may also send a signal to light up the appropriate indicator light to warn the vehicle’s user of a potential problem.
Diagnostic trouble codes (DTCs) are a combination of letters and numbers that indicate the nature and source of problems within a vehicle. While they don’t point to a specific cause, they can give clues as to how the issues can be addressed.
There are certain DTCs that warn the vehicle’s user about potential issues with a vehicle’s primary and auxiliary cooling fans. These DTCs include:
- P0480 Code: Cooling Fan Relay 1 Control Circuit
- P0481 Code: Cooling Fan Relay 2 Control Circuit
- P0482 Code: Cooling Fan Relay 2 Control Circuit
- P0493 Code: Fan Overspeed
- P0495 Code: Fan Speed High
If you suspect that there is a problem with your auxiliary fan control unit, you should conduct a thorough diagnosis. Make sure to rule out the most likely causes for the issue first before testing the least likely ones.
You can get reliable troubleshooting information with repair manuals and databases. These sources include diagrams and illustrations to make concepts easier to understand. However, if you’re not confident in your own repair skills, you can always have a professional do the job.
How Much Is a Replacement Auxiliary Fan Control Unit?
The price of aftermarket auxiliary fan control unit replacements range from $23 to $413. The cost depends primarily on the part’s compatibility with your vehicle’s year, make, and model. However, brand, series, and quantity may also affect the price. Auxiliary fan control unit replacements are sold individually or as part of a kit that typically includes installation hardware.
How to Replace Your Auxiliary Fan Control Unit
Imagine what a hassle it would be if you're driving while your ride brings out too much heat. Who would enjoy a trip like that? Hence, your auxiliary fan control unit is there to the rescue. It helps maintain the engine's temperature while working in tandem with the air conditioning unit. However, your auxiliary fan control unit can deteriorate over time. Once this happens, you must replace it immediately. Listed here are the steps that can show you how to do the task:
Difficulty level: Moderate
What you'll need:
- floor jacks and jack stands
- new auxiliary fan control unit
Step 1: The first thing to do is to disconnect the negative ground cable from your vehicle's battery terminal, so you can avoid any electrical accidents in the process.
Step 2: With the help of the appropriate screwdriver and a wrench, loosen up and remove the screws that hold certain components before gaining access to your old auxiliary fan control unit. For some vehicles, the piece that must be removed is the black plastic cover that is found above the radiator. But for some cars, the bumper on the front area may be required for removal.
Step 3: After removing the necessary components in order to have access to the old auxiliary fan control unit, you must use floor jacks, which should be supported by jack stands, in order to lift up the front area of your vehicle.
Step 4: For some models of vehicles, it may also be required to remove the covers of the fog lights. This can allow access the wiring of your old auxiliary fan control unit. However, that is not the case for other vehicles. Hence, you must refer to your ride's service manual ahead of time.
Step 5: Because your vehicle is already supported with stands, you must work on the underside to remove the cover of the bottom part of your radiator. Loosen the radiator's screws for this matter.
Step 6: You can now have full access to your old auxiliary fan control unit. Disengage the power connector that is connected to the fan with extra caution.
Step 7: Once the power connector is removed, loosen up and gently remove the bolts that fasten your old auxiliary fan control unit in place. Take off the unit afterwards.
Step 8: You may now install your new auxiliary fan control unit. Attach the bolts that you have removed earlier, and make sure that they are tightened securely.
Step 9: Reinstall the other components that you have taken off in reverse order. Start with the power connector.
Step 10: Before reattaching the other covers, it is time to test the performance of your new auxiliary fan control unit. Link the ground cable again to the car's battery terminal for this matter.
Step 11: After ensuring that your new auxiliary fan control unit is working well, you must turn off the engine once again, and start reinstalling the other covers that were removed.
Step 12: Remove the floor jacks and jack stands, and lower your vehicle on the ground carefully.