Fuses in cars and other electrical appliances play an essential role. They prevent high currents from damaging key circuits in a car. A fuse is a protective device with two terminals and a thin wire or metal strip running across the terminals.
It’s okay for a car fuse to blow at one point. Unfortunately, it is common in cars and electrical appliances in our homes.
You may have probably had a blown fuse if you’re a car owner. Fuses come in different amperages. The higher the amperage, the higher the electric flow it transmits to the key circuit.
Knowing how a blown fuse looks is a good step toward fixing it. Therefore, if you suspect you have a blown 40 amp fuse, you may ask, what does a blown 40 amp fuse look like?
In this article, the Rx Mechanic team will discuss what happens when they blow off, how to test 40 amp blown fuses and replacement procedures. Let’s start with the use of a 40 amp fuse.
What Is The 40 Amp Fuse Used For In Car?
The 40 amp fuse is used in vehicles to protect components from overcurrent and short-circuiting that require 40 amps to operate. This includes the ABS system, ignition, ECU, window regulator mechanisms, and AC fans.
When some of the components draw a stronger current than it is designed to handle, the 40 amp fuse gets blown in order to stop the current from traveling to the main component and burning it.
Basically, the larger the amperage, the more important and expensive the component is. So, instead of expensive components getting burned by drawing higher currents each time they malfunction, vehicle manufacturers came up with a $2 40 amp fuse that will get blown instead of the main component.
Today’s vehicles can contain up to 100 ECUs, maybe more. Each of the electronic control units has been designed for a specific job including ABS, power steering control, the way to power windows, seat heaters, and AC.
There isn’t room in the fuse box for each ECU, so many of them are protected by the same 40 amp fuse.
So, when some of these ECUs malfunction, they tend to draw more current from the battery than they are designed to withstand.
When this happens, the current travels from the car battery, into the 40 amp fuse. The 40 amp fuse detects that the current is too strong and instantly gets blown.
This action stops the high current from reaching the next stop which is the main component. By doing so, the 40 amp fuse protects the main components from getting burnt.
How Do You Test A 40 Amp Fuse?
There are three means of testing if a fuse is blown. These methods are easy to understand and quite effective.
They are visual inspection, using a test light, and using a multimeter. Using a multimeter is more popular amongst DIY car owners and service technicians. But first, let’s see how to tell if a fuse is blown without a multimeter.
Visual Inspection
Whenever I have blown a fuse in my car, I’ll first do a visual inspection of the fuses. However, visual inspection is mostly for blade-style fuses like 5 amp, 10 amp, 15 amp, and 20 amp. It may be tricky to track a blown cartridge-style fuse by visual inspection.
In any case, 30 amp and 40 amp fuses have blade style and cartridge style fuses. First, inspect the wire that runs across the two fuse terminals and see if it is discontinued.
If you have a cartridge-style fuse, remove the plastic cover on top to have a clear view of the metal strip across the fuse probes. If the wire is broken, the fuse is bad and needs replacement.
Using Test Light
Test lights serve several purposes. First, it is a common tool that every automotive technician should have. To test a 40 amp fuse first, connect the wiring harness to your negative battery terminal.
Then, touch the metal pin on the positive battery terminal. If the bulb in the test light illuminates, it shows a proper connection.
Next, locate the 40 amp fuse and touch the test light metal pin on the fuse terminals. Both terminals should light up. If only one illuminate or none of them light up, you have a blown fuse that needs replacement.
Using Multimeter
Testing a blown 40 amp fuse with a multimeter is straightforward. To check a blown fuse with a multimeter, Locate and pull out the fuse.
After that, set your multimeter to ohm settings. Connect the multimeter probes properly. Then, touch the two probes and note the reading.
Touch the probes on each fuse terminal. You should have the same or similar results. If you have a different reading or no reading, the 40 amp fuse is bad.
What Does a Blown 40 Amp Fuse Look Like?
A blown 40 amp fuse is characterized by a broken or disconnected metal alloy strip or thin wire inside the fuse, often with signs of burning or discoloration.
When a 40 amp fuse gets blown, the metal alloy strip or thin wire inside will look like it is broken. The 40 amp fuse has copper contacts on both sides and a metal alloy strip or thin wire running from one copper contact to the other.
When the 40 amp fuse gets blown from a high current, the fuse wire in the middle of the cartridge melts and prevents further electricity flow.
A 40 amp fuse is designed to withstand 40 amps of electricity. If for some reason a higher current is being drawn from the main component, the 40 amp fuse will get blown and prevent the main component from being damaged.
A properly working 40 amp fuse has a metal alloy strip that acts like a bridge between two copper contacts.
When current comes from the car battery, it enters one copper contact and then flows through the metal alloy strip, into the other copper contact, and to the main component.
However, when a higher-than-normal current is being drawn from the car battery, the high current will enter one copper contact, but the metal alloy strip will melt.
No current will flow into the other copper contact and into the main component. By doing this, the 40 amp fuse prevents further damage to the main component says Piston Heads.
Symptoms of a Blown 40 Amp Fuse
- Loss of Power: The electrical component or system protected by the fuse will stop working.
- Warning Lights: In some vehicles, a warning light on the dashboard may illuminate.
- Frequent Fuse Failure: If the same fuse keeps blowing repeatedly, it’s likely there is an underlying issue.
- Smoke or Burn Smell: In severe cases, a blown fuse may produce a faint smell of burning or smoke.
- Visual Signs: Upon inspection, the fuse may show signs of damage, such as a broken wire or discoloration.
What Causes a Blown 40 Amp Fuse
- Overcurrent: If the current flowing through the fuse exceeds its rated capacity (40 Amps in this case), it can cause the fuse to blow.
- Short Circuit: A direct connection between the positive and negative terminals, bypassing the normal load, can cause a sudden surge of electricity, leading to a blown fuse.
- Aged or Worn Out Fuse: Over time, fuses can deteriorate and become more susceptible to blowing, even under normal electrical conditions.
- Faulty Electrical Components: If an electrical device or component connected to the circuit is faulty, it can draw excessive current and blow the fuse.
- Incorrect Fuse Rating: If a fuse with an incorrect rating has been used, it may not be able to handle the load and could blow.
What Happens When A 40 Amp Fuse Blows?
Now that we’ve seen several ways to test a blown a fuse and what it looks like, what happens when a 40 amp fuse blows?
Both blade style and cartridge style 40 amp fuse has a transparent view through which you can see the metal ribbon across the copper terminals. If the fuse blows, the metal ribbon will melt or cut and stop the electric flow from traveling to the other end.
They’re taking shots for the corresponding circuit or component by discontinuing the electric flow. Therefore, these components will not work until you replace the blown fuse.
However, I’ll not recommend you bypass a blown fuse for any reason. If you bypass any fuse, you’re sending direct current to the main current and exposing it to overcurrent.
How To Change Blown 40 Amp Fuse?
Knowing how to change a blown 40 amp fuse will save you from unnecessary grammar in a mechanic garage from a service technician who may want to rip you off.
This means it’ll save you from unnecessary expenses. A 40 amp fuse should cost $1.5 to $2, but an auto technician will charge you $100. Here’s how you can replace a blown 40 amps fuse at home.
Step 1: Buy a new 40 amp fuse.
Fuses are one of the cheapest automotive parts. They cost between $1 to $2. So, instead of buying a single 40 amp fuse, you can buy it in packs.
However, I recommend getting one from your local auto shop because shipping fees from an online store will be more costly than the part itself.
Step 2: Find the fuse box.
Vehicles have different designs. Therefore, auto manufacturers have different locations for the fuse box.
However, most vehicles have fuse boxes underneath the steering wheel, behind the driver’s door, and in the engine bay. You’ll likely see the 40 amp fuses in the engine bay.
So, open the hood and locate the fuse box. It is a black plastic box next to the battery with ‘Fuses and Relay’ written on top.
Step 3: Locate and pull out the burnt 40 amp fuse.
Open the fuse box by depressing the clips on the cover. You’ll see mounting bolts on some vehicles.
Loosen the bolts to access the fuses inside. Next, locate the blown fuse and pull it off. You can either remove it by hand or use a pair of pliers. Whichever works best for you. Once the fuse is out, proceed to the next step.
Step 4: Test the fuse.
Test the fuse and confirm you’re replacing the blown one. You can test it by visual inspection, using a test light, or using a multimeter. Check the testing guides above and follow the instructions in checking the blown fuse.
Step 5: Snap in the new 40 amp fuse.
Ensure there is no dirt or debris on the port. You removed the blown fuse. After that, gently snap in the new 40 amp fuse. Finally, close the fuse box using the reverse process.
FAQs.
Q: How can I identify if a 40 amp fuse is blown?
To identify if a 40 amp fuse is blown, you can visually inspect the fuse element inside the fuse housing. If the element appears broken or burnt out, then the fuse is most likely blown.
Q: Can a blown 40 amp fuse cause a complete power failure?
Yes, a blown 40 amp fuse can cause a complete power failure in the circuit it protects. When a fuse blows, it opens the circuit and stops the flow of electricity.
Q: How can I replace a blown 40 amp fuse?
To replace a blown 40 amp fuse, you need to first identify the location of the fuse in your electrical system. Once located, you can carefully pull out the blown fuse and replace it with a new one that has the same ampere rating.
Q: Are there any safety precautions I should take when dealing with blown fuses?
Yes, it is important to take safety precautions when dealing with blown fuses. Always disconnect the power source before replacing a fuse, and use insulated tools to avoid electrical shock.
Q: Can a blown 40 amp fuse be caused by an electrical overload?
Yes, an electrical overload can cause a blown 40-amp fuse. When the current flowing through a circuit exceeds the fuse’s rating, the fuse will blow to protect the circuit from damage.
Q: Are there any specific tools required to replace a blown 40 amp fuse?
Generally, no specific tools are required to replace a blown 40 amp fuse. However, it is recommended to have a fuse puller or a pair of needle nose pliers to safely remove the fuse.
Q: Can I use a higher ampere-rated fuse to replace a blown 40 amp fuse?
No, it is not recommended to use a higher ampere-rated fuse to replace a blown 40 amp fuse. Fuses are designed to protect the electrical circuit and using a higher rated fuse can potentially cause damage or overheating.
Q: Should I consult a professional if I am unsure about replacing a blown 40 amp fuse?
If you are unsure about replacing a blown 40 amp fuse, it is recommended to consult a professional electrician. They have the knowledge and expertise to safely handle electrical systems and can ensure proper fuse replacement.
Final Words
It is okay for fuses to blow. In fact, it’s a normal occurrence with vehicles. However, a blown 40 amp fuse may prevent your heater seats, AC system, ignition system, or ABS from functioning.
You may replace this component without knowing you have a blown 40 amp fuse. However, knowing what a blown 40 amp fuse looks like will help you avoid making this costly mistake.
We don’t want you to make such a mistake entailing your wallet. That’s why we answered the mind-boggling question, ”What does a blown 40 amp fuse look like?” and guiding you on how to test and replace it.