Q: Does My Car Have a Blown Fuse?

One of the more common electrical problems that both domestic and import vehicles have are issues with the fuses that supply power to individual components. The fuse system is used for circuit protection and prevents a circuit overload of high amperage, which creates heat and damage to the wiring of the system or the component that is operating. When an electrical short occurs or more power is sent through the fuse system than should, the fuse will break, shutting down electrical power to the component until the fuse is replaced and the electrical problem is solved.

Most car, truck, and SUV owners assume that if an electrically powered component does not work, it must be a blown fuse that is causing the problem. In many cases they’d be correct. However, fuses don’t blow or break for no reason. Most of the time, the fuse issue is caused by a disruption of electrical flow within the component that is being powered by the fuse. This can include:

• A frayed or damaged electrical wire that is exposed
• A cross wired electrical signal that is not relaying the electrical signal throughout the circuit
• A relay that is damaged
• An electrical short inside the component

Unless the error is repaired that is causing the fuse to break, this problem will continue and more fuses will break.

How does a fuse work?

There are many fuses and circuits that need to be protected on a vehicle. Each circuit is rated for the amperes that it uses to operate properly and safely. Fuses also have an ampere rating with common ratings of 5, 10, 15, 20, 25, and 30 amps. When this rating is exceeded, the fuse breaks. Fuses can protect multiple circuits and provide a path of electricity to flow through the circuit. If the circuit or component draws more amps than the rating on the fuse, the fuse will open, causing no flow of electricity to that component.

For example, if the radio component draws more amps than the rating of its fuse, the radio would be inoperable because the fuse will open. Any component that uses electricity in the vehicle is protected. Therefore, if your car has a blown fuse, you should have a technician replace the fuse as soon as possible. However, it’s also important for the mechanic to determine why the fuse has broken so that the issue is not repeated. This is typically completed with an electrical system inspection.

During an electrical system inspection, an ASE certified mechanic is trained to locate the component that is powered by the blown fuse and complete a diagnostic inspection of the component using an electrical probe or tester. They will test the connections on the component to ensure the circuit is complete; (meaning it has electrical continuity) and that the component is receiving power from the fuse. If there is a problem with the component that needs to be fixed or replaced, the mechanic will let the customer know before they make the repair.

Fuses are not part of a routine maintenance check because they should last the lifetime of the vehicle, but it is possible that a fuse will blow and require attention to return functionality to electrical car components. If you have any problems with your electrical system, check your fuses to see if they are broken and contact a local ASE certified mechanic to complete an electrical inspection.