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HomeTips & GuidesAutomotive fan Relay Wiring: How to Replace a Cooling fan Relay

Automotive fan Relay Wiring: How to Replace a Cooling fan Relay

About Automotive fan relay wiring, We all know that most car engines are liquid-cooled. They have a circulating coolant, which absorbs and carries away combustion heat from the block and the cylinder head to the radiator, where it is released into the specially designed and positioned fans. That is why a radiator is technically known as a “heat exchanger.”

However, the radiator fan can stop working when the fan relay fails or malfunctions. Learning more about the automobile fan relay wiring will help you fix this issue promptly. Let’s see how!

Table of Contents

How does an automotive fan relay work?

You can think of a relay as an electromagnetic or an electric leveler that uses a fairly small current. 

When electricity flows through a coil of wire, it becomes a temporary magnet, thus switching ON/OFF, another component that uses a much larger electric current.

A cooling fan relay is used on cars with an electrical fan to cool the engine.

An automotive cooling fan relay converts low-voltage signals from a thermostatically controlled sensor or the electronic control module (ECM).

By taking a low voltage signal and internally switching ON the relay, the cooling fan relay allows for the supply of battery voltage to the radiator cooling fan.

When the engine temperature reaches unsafe levels, the car’s temperature switch powers ON the cooling fan relay. The activated cooling fan relay will complete the circuit, allowing electric current to flow to the fans.

Since a lower voltage signal controls the relay, there is less stress on the rest of the charging and wiring system.

Moreover, an automotive fan relay allows for the utilization of a smaller-diameter wiring harness that takes up less space throughout the car.

Automotive fan relay wiring

Automotive fan relay wiring

Fan relay wiring Diagram

Relays are used to perform types of jobs on a car, from engine control components to accessories. A radiator fan is one of the most vital underhood components operated by one relay.

The car air conditioner includes a condenser (heat exchanger often mounted in front of the radiator) that also needs airflow. So,  there will be two fans sometimes.

Those with 2 fans can sometimes have one of the two fans energized depending on the prevailing conditions. Also, they often have a module controlling fan speeds by using two or three relays that work together. As such, both fans will run together in parallel at high speed(both fans receive full system voltage simultaneously) or in series (the voltage is split, and the fans run at low speed).

Automotive relay

Automotive relay

How to know if an automotive cooling fan relay is bad?

If the fan fails to start, there could be an issue with the cooling fan relay. Fortunately, There are multiple ways to tell if a faulty cooling fan relay is the cause.

Swapping relays:

If the cooling fan doesn’t start, swap the relay for a new one to see whether the previous (original) relay was the problem. This method only works if a single relay operates the fan.

It may not function if many fan systems have a module or two or three cooling fan relays working together.

The good news is that most auto relays have a similar design, which allows you to swap your relay with another from a different non-critical system.

However, this can be risky on newer car models. So, avoid swapping relays with varying part numbers, even if the terminals appear similar.

If the fan functions with the swapped relay, you will know your automotive cooling fan relay system is faulty.

Measure the resistance of the relay coil.

You can also measure the resistance of the relay coil. Generally, a relay coil’s resistance should read between 40-80 ohms.

A lower resistance will mean that the relay coil has broken down, while a higher reading will imply that the relay coil has started to fail.

Listen for noises.

Another DIY test entails shaking your cooling fan relay and listening for any noises. A broken or malfunctioned armature will rattle around the relay.

Thump or bump the relay.

Listen to your relay to see if it “clicks” when energized. However, this does not mean the relay is good, as it can “click” and still fail to deliver power to the fan.

How to replace a cooling fan relay on most vehicles:

The cooling fan relay is usually mounted to the electric fan assembly behind the radiator or the underhood fuse and relay center. To replace your automotive cooling fan relay, you can use one of the following methods:

Method 1: Replace the cooling fan relay in the underhood fuse or relay box.

Step 1: Find the underhood fuse or relay box.

Visually locate the underhood fuse or relay box. This box is usually found on the engine compartment’s passenger or driver side near the fender.

Step 2: Remove the fuse or relay box cover.

Remove the relay or fuse cover from the top of the underhoof relay or fuse box. You can accomplish this by releasing or removing any combination of fasteners or retaining slips.

Step 3: Identify the cooling fan relay.

You need to identify which relay is the cooling fan relay. Most manufacturers often print a diagram on one side of the underhood relay or fuse box cover, which maps out the position of each relay and fuse included in the box.

TIP: If there is no diagram, check the manufacturer’s manual for a possible listing of relay and fuse locations.

Step 4: Ensure the power is OFF.

Ensure the ignition key is in the “OFF” position. Pull the key out of the ignition and set it in the center console (if equipped) or on the dash to enhance safety.

Warning: The ignition must be in the OFF position to prevent voltage spikes that can result in fatal damage to your ECM when replacing your automotive cooling fan relay.

Step 5: Replace the cooling fan relay.

Pinch the relay gently using your fingers and twitch back and forth while pulling on your relay. The relay will pull free with minimal effort.

TIP: It is not unusual for the relay to build up debris and dust over time, which become hard to remove. Sometimes, using a pair of pliers or a small screwdriver is essential to coax the relay carefully out of its cradle.

Step 6: Match your replacement relay to the original relay.

Once you remove the cooling fan relay, compare the replacement relay to the original one you removed. Make sure that they are of the same dimension.

You should also flip over the relay and compare the orientation and number of the terminals.

Step 7:Install a new automotive cooling fan relay.

Place the replacement (new) cooling fan relay above the recess where you removed the original relay. Next, press it gently into position.

Step 8: Check if the replacement cooling fan relay is seated properly.

Inspect the base of your replacement cooling fan relay to verify that the relay’s base is seated properly and completely into the socket.

There should be less than a one-millimeter gap between the underhood relay or fuse box and the base of your relay.

Step 9: Check the operation of your replacement automotive cooling fan relay.

Verify the working of the new replacement cooling fan relay by energizing it. You can do this by turning the air conditioning system on or warming the engine to operating temperature.

Automotive cooling fan underhood

Automotive cooling fan underhood

Method 2: Replace a cooling fan relay in the electric cooling fan assembly.

Step 1: Find the automotive cooling fan relay.

Inspect your electric cooling fan assembly visually to locate the cooling fan relay.

TIP: You can use a workshop repair manual to identify the cooling fan relay.

Step 2: Disconnect the electrical connector.

A cooling fan relay features an electrical connector that you should disconnect and switch over to the replacement cooling fan relay. The most popular type of connector is the push-type connector.

Therefore, disconnect your electrical connector and remove your cooling fan relay.

Step 3: Compare or match the replacement cooling fan relay to the original one.

Inspect your new (replacement) cooling fan relay visually and compare it to the original one you removed.

Pay particular attention to the physical dimension of the replacement relay (the orientation and number of pins).

Step 4: Mount the replacement cooling fan relay.

Hook your electrical connector into your fan and mount it back into position.

Step 5: Check the operation of your replacement cooling fan relay.

Verify the functionality of your replacement relay by energizing it. You can do this by switching the air conditioning system ON or warming the engine to operating temperature.

The good news is that most manufacturers design their cooling fan systems with the air conditioners switched ON.

Relay wiring harness wiring 

Relay wiring harness wiring 


Replacing your automotive cooling fan relay is essential to keeping your vehicle running properly.

If you need further assistance with replacing your car’s cooling fan relay wiring harness/socket wiring harness/pigtail wiring harness, Cloom’s certified and experienced technicians come to your business.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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