If you’re unable to successfully start your car as each start attempt blows the starter motor fuse then read on.
This post outlines why your starter motor fuse keeps blowing and what you can do to fix the underlying cause so that you can get the car engine starting consistently again.
What Causes a Car Starter Fuse to Blow?
The car starter fuse may blow if:
1. Short in the starter motor wiring
If the car starter motor fuse keeps blowing when you turn the ignition key to the ACC, START, or ON positions it’s because there’s a direct short to ground that’s made when the key is turned and the resulting current flow exceeds and blows the car starter motor fuse.
2. There is a short in the solenoid relay coil that’s causing the fuse to blow. The coil should measure a resistance reading of several ohms and not a direct short (zero ohms).
If it’s a direct short then there’s a problem and you should replace the solenoid relay. Check if this clears the problem.
3. Faulty starter. It is also possible that the starter has an internal short and needs to be replaced. Arrange to have the starter removed and tested.
Replace the starter with another of the same rating and check if this solves the problem.
Locating the cause – what to do
What you need
- A wiring diagram
- A current tester preferably of the clamp that allows you to measure DC current flow by applying the clamp meter around a wire
- A 50 watt DC bulb to simulate the fuse blow
1. Use a DC bulb to simulate the starter motor fuse blow
To avoid burning out several 40-60 amp fuses as you troubleshoot the fault, connect a 50-watt DC bulb to the starter fuse location.
This way, the light coming simulates a fuse blow and saves you the cost of blowing several starter motor fuses as you locate and test the underlying fault.
2. Use a schematic to locate the short
Use a schematic or wiring diagram to follow the wires protected by the car starter fuse. Look out for:
- burnt-out wire sections,
- bare wires that may be touching each other, and
- chaffed wires that may be rubbing against brackets and shorting.
Inspect the wires connected to the ignition switch and protected by the starter motor fuse including the circuits they may be fed off it (follow the schematic) checking for any short.
After you locate and fix a damaged section, test again by turning on the ignition switch, and checking if the test light comes on.
Once you’ve identified and fixed the shorting wire, you can then replace the test bulb with the 40 amp or 60 amp automotive fuse as recommended by the car manufacturer.
Why Your Car Starter Fuse Keeps Blowing
Simply replacing the starter motor fuse without identifying and fixing all the shorts in the wiring will cause each fuse replacement to blow.
There could be one or more shorting wires or even an intermittent short that happens when an ignition switch wire connects with a grounded bracket for example.
Perhaps it is a case of wires chaffing again and in addition to replacing the damaged wires, they need to be mounted or applying a new sheath.
Follow the steps outlined to locate and fix the underlying short circuit.
The car starter fuse will keep blowing if the short to the ground persists.
Take you time and make sure you carefully look along the length of the connecting wires for chaff marks or burns marks.
Signs of a Blown Car Starter Fuse
With the starter motor fuse blown, the car will not be able to start. The car engine will not crank (and the starter motor will not rotate too).
Note that this is not a conclusive test as you can have the same signs with a weak or damaged car battery, and loose or damaged battery wire connections too.
How to Tell that The Fuse Has Blown
Visually inspect the car starter motor fuse or test the fuse for continuity using a digital multimeter to confirm if it is blown or not.
To confirm that the car starter fuse has blown, locate the car starter fuse in the fuse box. Remove it and inspect the fuse wire inside the glass fuse body. If the fuse is blown, the fuse wire inside will be broken.
You can also use a digital multimeter set to read continuity and place one probe on one metal leg of the fuse wire and the second probe on the second metal leg of the fuse.
The meter will show an open circuit condition or there’ll be no continuous tone from the meter if the fuse is blown.
You may also be interested in this post: Car starter motor works intermittently – is it possible and what to do
What the Fuse Looks like
The car starter motor fuse is usually an automotive-style 40-amp or 60-amp fuse. It is usually located in the fuse box under the hood next to the battery. Refer to the fuse layout diagram under the fuse box cover to confirm the fuse location.
Why a starter motor fuse
The car starter motor fuse protects the starter motor wiring from burning out from excessive current draw in case of a fault in the wiring or the starter motor itself.
Without the fuse, there’ll be extensive damage to the wiring and possibly a fire should the be a short.
Replace the starter motor fuse with one that’s recommended by the car manufacturer.
If the car starter motor fuse keeps blowing then there’s a short to ground in the connected wires. This may be caused by exposed wires touching each other or connecting to a grounded metal bracket.
Always replace the blown fuse with another with the rating (amps) recommended by the manufacturer.