Blown car battery fuse causes, symptoms and fixes

Car main battery fuse is a relatively high amp fuse that protects overall battery circuit. When it gets blown, it causes no crank or accessories not working.
Last modified
11 Feb, 2024

As little or as cheap as a battery fuse is, it is a vital component of a car because without it, the car will be rendered useless.

Generally, fuses are used to protect electrical circuits. They get blown instead of what they are protecting to get damaged.

Fuses are of different types and sizes, depending on the application.

Blown battery fuse causes, symptoms and fixes

Fuses are important electrical safety components used to protect loads against high current and for short circuit protection.

They are thin strips of electrical conductors that heat up and melt when a current that is above the current designed for it to withstand passes through it, thereby protection the load that it is connected to. Fuses are relatively cheap components making replacement easy to do and making having several spares easy.


How many terminals does a fuse have?

A fuse has two terminals. It is not a component that has polarity but rather a conductor that easily melts/breaks when high current passes through it.


What is a car battery fuse? 

A fuse that is connected to the battery protects the main supply circuit to loads. Aside the battery fuse, there are other smaller rated fuses that are directly protecting individual loads. The battery fuse is the first line of defense to the electronics in the vehicle.


Symptoms of a bad battery fuse

Below are the symptoms of a bad battery fuse:

1. No crank.

2. No lights in the dash.

3. Accessories like central lock, power windows and so on not working.


Where is battery fuse located?

Depending on vehicle design, battery fuses can be located in the following areas:

1. At the battery terminal connector.

2. At power fusebox in the boot area.

3. At the main fuse box in the engine bay.


How many battery fuses are present in a car?

Some cars have a single battery fuse while others have more than one to protect different groups of electrical loads.


Causes of blown battery fuse

1. Battery terminal reversal: This happens when the positive and negative terminals of battery are interchanged.

2. High current: A high current that passes through the fuse will break it.

3. Short circuit: A short circuit allows passage of maximum amount of current in the circuit. This melts and breaks the fuse.

4. Faulty wiring.


How to identify/test a blown fuse

There are three ways to identify a blown fuse as follows:

1. Physical inspection: This involves looking at the thin conductor of the fuse for breakage. Many fuses have transparent cover that makes it possible to see the conductor of the fuse.

2. Continuity test: This is carried out using a multimeter in the continuity range or an ohm meter in the lowest ohmic range. A good fuse should have zero ohms resistance, in other words, it should not be resistive. A broken fuse will show OL (open loop) or infinite ohms value. It is possible for it to show very high resistance value if it is still connected in the circuit even when it is broken.

3. Voltage test: This is carried out using a volt meter or a multimeter in voltage range. A broken fuse won't allow current to pass. This will create a potential difference across the terminals of the fuse. At one terminal, battery voltage is present and at the other terminal, no voltage is read.

How to fix a blown fuse

A blown fuse requires replacement with a new one of same amperage rating. For instance, an 80 Amps fuse should be replaced with same rated fuse. Putting a fuse with higher rating puts the load at risk as it will not have the appropriate over current protection for the intended load anymore. Putting a lower rated fuse can cause the fuse to be getting blown often as the load draws current that is above that which the fuse can withstand.


Can ordinary conductor/wire be used in place of a fuse?

A wire should not be used as replacement for a fuse as this will not protect the load and is a potential fire hazard since the wire can heat up yet refuse to break on time or refuse to break at all.


Battery fuses protects electronic components and not the battery

There is a common misconception that the battery fuse protects the battery. This is actually not true. It is the first line of defense to protect control units, wiring and other electronic components in the car.


Since fuses are cheap and not scarce, it it good to have extra fuses of different amperages in case of an emergency to quickly fix faults due to a blown fuse.