How to Tell if a Car Fuse is Blown?

In electronics, fuses serve as safety mechanisms to prevent the overflow of current which can damage an electrical circuit. A fuse is typically a metal wire strip that melts or burns when too strong a current passes through it, thus interrupting the flow of electricity and breaking the circuit to a given device. A car has many such fuses to protect its various electrical components from high voltage occurrences. These fuses are generally rated at 32 volts and are in one of two fuse boxes for most vehicles.

How to tell if a car fuse is blown

When a component in a vehicle stops working, the reason is most often a blown fuse due to an overabundance of electrical current. This could apply to everyday driver-interfaced devices like a car stereo or interior lighting but can also include more sophisticated systems powered by electricity: powertrain electronics, chassis electronics, safety features, driver assistance technologies, and passenger comfort amenities. When a failure occurs, the bad fuse needs to be located and replaced. Replacement fuses can be found online and at virtually any store with an automotive department.

Why Fuses Blow

A blown fuse signals a short circuit. This occurs when an electrical component draws a stronger current than it is designed to handle due to the device malfunctioning. Defective switches and faulty wiring are common causes for fuses blowing, but any kind of mechanical issue with a motor or an electrically motivated moving part can be a culprit. For instance, a windshield wiper stuck under ice can force the motor to short out. In this case, the blown fuse prevents the motor from overworking and burning itself out, which would be a much more costly replacement than the fuse.

In normal failures, such as with lights, power seats, or air-conditioning, checking the fuse is the logical first step to resolving a problem. But for a vehicle’s more complex engineering systems, the recommendation is for the car owner to investigate the reason for the blown fuse as it might be indicative of a larger issue that could continue to grow worse, even after the fuse has been replaced. Consulting with a certified mechanic or dealer service department is advised.

Locating a Blown Fuse

Once you suspect a blown fuse, turn off the vehicle and locate the main fuse box. In most cases it is in the driver’s side footwell underneath the dashboard. There may also be a second fuse box under the hood. Consult your owner’s manual for the exact location of each. 

In most cases, a diagram that shows you the position and the name of each fuse can be found inside the fuse box. This will help you locate the fuse that is related to the vehicle component that has failed. But pay close attention to the diagram, as a typical vehicle may have over 30 fuses, and higher-end cars with more electronics may have two to three times that many.

Once you identify the right fuse, pull it out (ideally with fuse pullers/pliers) and visually inspect it. The blown fuse will be apparent because the wire element within will have melted or burned from the higher electrical current. You can also use a test light or a multimeter to identify the dead fuse without having to pull it out. Both tools are affordable and easy to use.

Replacing the Fuse

After verifying the blown fuse, obtain a new fuse that is identical to the one you’re replacing. There are three primary types of vehicle fuses: squarish plastic fuses with twin prongs, cylindrical glass fuses, and cylindrical plastic fuses. All of them use burnable or breakable filaments. It is important that the new fuse is the same type and voltage because replacing a fuse with a different voltage can cause damage to the component the fuse is supposed to be protecting.

Simply insert the new fuse in place of the old one and make sure it is all the way in. A quick comparison to the fuse next to it will let you know if it is properly set. Then return the fuse box panel to its normal state and turn the vehicle on. Next, test the component to see if it works with the new fuse in place. If it does, the replacement was a success. If it does not, contact an automotive professional to further diagnose the issue.