How to tell if a car fuse is blown?
A blown car fuse usually means the circuit stops working, and you’ll often see a broken filament in a glass fuse or a melted/overly dark metal strip in a blade fuse. You can confirm with a fuse tester or multimeter and replace with the same amperage rating.
This guide walks you through identifying a blown fuse, confirming the diagnosis with measurement tools, and replacing it safely, including what to do if fuses keep blowing and how to distinguish a true fault from a simple replacement task.
Quick visual checks
Before you reach for a tester, it helps to know what you’re looking at. Different fuse types show different signs of failure, and a careful look can speed up the diagnosis.
Glass fuses vs blade fuses: what to look for
Glass fuses and blade fuses reveal damage in distinct ways. Use these cues to guide your inspection.
- Glass fuses: a visibly broken or shattered filament, a darkened or cloudy glass, or a melted end near the metal caps.
- Blade fuses: a visibly broken or melted internal metal strip, scorched plastic around the ends, or a fuse body that looks deformed.
- In some cases, the device or circuit protected by the fuse remains dead even if the fuse looks intact; visual signs are helpful but not definitive.
Visual signs strongly suggest a blown fuse, but they are not a guaranteed diagnosis. A continuity check provides definitive confirmation.
Confirming with a tester
To verify with a tool, use a dedicated fuse tester or a multimeter set to continuity or resistance.
- Power down the vehicle and remove the key. If you’re working near the engine or high-current circuits, consider disconnecting the negative battery terminal for safety.
- Remove the suspect fuse from its slot using a fuse puller or insulated pliers.
- Test for continuity across the fuse’s two ends. A good fuse shows continuity (low resistance or a beep); a blown fuse shows no continuity (infinite resistance).
- If testing in-circuit, remove the fuse from the circuit to avoid reading other components and compare the result to the fuse’s rating.
Performing a meter test helps confirm whether the fuse itself is the problem or if another fault is pulling current through the circuit.
Replacing a blown fuse safely
If the fuse is confirmed blown, replacement is straightforward but must be done with care to avoid damage or fire risk.
- Identify the correct amperage rating and fuse type from the old fuse or the vehicle manual. Use the exact same value and style (blade or glass).
- Insert the replacement fuse firmly so it seats fully in the holder.
- Restore power and test the circuit to confirm operation. If the fuse blows again, the fault lies elsewhere in the wiring or the connected device.
Never replace a blown fuse with a higher-amp fuse to bypass a fault. Elevating the rating can overheat wires and cause a fire.
Dealing with recurring fuse blows
Repeated fuse failures usually point to a short circuit, a device drawing more current than intended, water ingress, or degraded wiring. In such cases, seek a qualified automotive technician to diagnose and repair the underlying issue.
Summary
Diagnosing a blown car fuse combines a quick visual check with a definitive continuity test. Use the correct amperage rating when replacing, and investigate any fuse that repeatedly blows to prevent further damage or safety hazards.
