What Are The Symptoms Of A Bad Alternator?

Usually, people would think that there is a problem with their battery if their car if it doesn’t start.  But in reality, your car battery may be fine and you really are looking at a problem with your alternator. 

So what are the symptoms of a bad alternator? The main symptoms of a bad alternator are dim headlights, an alternator warning light,  a dead or weak battery, or odd electrical problems. One or all of these symptoms can indicate that you have a problem with your alternator.

But how do you know for sure that you have a problem with your alternator and not a problem with your car’s battery? And how can you test your alternator to make sure it’s putting out the correct voltage to your battery? Keep reading to find out.

What Is An Alternator? What Does An Alternator Do?

An alternator is an electrical generator that uses mechanical energy to create electrical current to supply power to the electronics of your vehicle.  An alternators job is to produce electricity that can then be fed to your battery and other electrical systems of your vehicle. 

Your vehicle’s alternator is designed to continuously feed electrical energy to your battery and other electrical systems when your car’s engine is running. That is why if your alternator is not running to its full ability why you can start to have trouble with your car starting.

If you are interested in learning more in-depth about how an alternator is able to generate the electricity that is then sent to your car’s battery check out the video below.

Symptoms Of A Bad Alternator

The list below will go into detail about the main symptoms of a bad alternator so that you know what to look out for.

1. Headlights Are Dim Or Flickering

Your alternator is in charge of providing electricity to your headlights so that you can see down the road at night.  One of the symptoms of a bad alternator is dim or flickering headlights.

If your alternator is starting to fail it won’t be able to provide as much power to your headlights which will make them dim or flicker.

2. Alternator Warning Light

Most modern vehicles will have a dashboard warning light indicating that there is something wrong with the electrical system.  This can be a warning light that says ALT or GEN but it may also look like the top of a battery.

If you see this light on your dashboard this is definitely one of the symptoms of a bad alternator and you likely have a problem with your alternator and need to get it checked out.

3. Battery Is Dead Or Weak

If your battery is dead or struggles to start when you go to start up your car this can also one of the symptoms of a bad alternator.  If your alternator is not putting out enough voltage to charge your car battery then eventually the battery charge will become low.

If your battery charge gets low enough then you won’t be able to start up your car the next time you try to start it. If you’ve recently replaced your battery then there is likely a problem with your alternator.

4. Odd Sounds

Another of the symptoms of a bad alternator is odd sounds coming from the hood of your vehicle.  Your alternator has bearings inside of it which can eventually wear out. As your bearings are worn down they can create a whining or grinding sound.  If you can pinpoint a weird noise coming from your alternator then it may need to be replaced.

5. Your Car Stalls or Dies While Driving

If you are driving down the road and your car randomly stalls or dies this can be another symptom of a bad alternator.  Most vehicles today use an ECU which is essentially the brain of the vehicle to tell the engine how to operate under throttle and to keep the engine running.

If your alternator is not able to provide enough power to your battery this can cause issues with your ECU which can cause your car to stall or die when you are driving down the road.

6. Electrical Issues

Like I mentioned earlier the main job of your alternator is to provide electricity to your vehicle to power the various electronics in your vehicle.  These are things like the sound system, door locks, power windows, heated seats, etc.

One of the symptoms of a bad alternator is that parts of your electrical system may start to act up or fail altogether.  If you notice the lights on your dashboard are dim or flickering there may be a problem with your alternator.

How To Diagnose A Bad Alternator

Follow the steps below to determine if you have a bad alternator or to determine if there is something wrong with your battery.

1. Take Your Car To Have The Alternator Tested

If you take your vehicle to your local auto parts store to check your battery they can also check your alternator while you are there to let you know if there is an issue with your car’s battery or alternator. 

They have an alternator tester that they can bring out to hook up to your car to determine if your alternator is bad or if there is potentially something wrong with the battery.

2. Alternator Voltage Test

If you don’t plan on taking your car to the auto parts store you can also check your alternator yourself using a multimeter.

You can use a multimeter to get a reading off of your car battery by hooking up the black end of the multimeter to the ground connection of your battery and then connecting the red end to the positive connection of your battery.

Your car’s battery should be reading at least 12.6 volts when your engine is not running. If your battery levels are lower than 12.6-13 volts when your car is off that is a good sign that your battery is being drained or your alternator is not providing enough charge to the battery when the vehicle is operating.  

You should also get a reading from the battery while the engine is running, this reading will be higher than the reading you would get while the engine is off as your alternator will be sending electricity to the car battery.

Your battery should be reading 13.7 to 14.7 volts when your engine is running. If your battery is reading less than 13.7 volts when your car is on this is a sign of a bad or faulty alternator.

If however you get a reading on your alternator and it says it is putting out 13.7 to 14.7 volts and you have had your battery checked you would want to see what may be potentially be draining your battery.

I’ve included a video from ChrisFix below that explains the process in more detail if you are more of a visual learner.

3. Battery Test

You would first want to rule out that your battery is not bad before you decide to replace your alternator.  If you have a multimeter on hand you can use the multimeter to get a reading of the voltage that your vehicle’s battery is currently putting out.  

If your battery is fully charged it should be reading anywhere from 12.6 volts to 13 volts. If your battery is reading within that range you would probably want to find a way to jump your vehicle so that you can take it to a local auto parts store to get your battery tested.

They will test your battery at your local auto parts store for free and let you know if it needs to be replaced. If your vehicle’s battery does need replacing they will usually give you the option of replacing your battery on the spot for you for free as long as you pay for the new battery.

If you take your car to your local auto parts store and they say that your battery levels are fine you would want to next take a look at your alternator.

4. Battery Parasitic Drain

If your vehicle allows you to charge electronics inside of it while the vehicle is off you would want to make sure that you don’t leave something plugged in when you go to turn off your vehicle. 

It’s alright to charge your electronics using a vehicle charger while the engine and alternator are running but if you are charging your personal electronic devices while the vehicle is off you will be pulling this electricity directly from the battery and not the alternator.

If you have any sort of aftermarket stereo system or alarm you would also want to check your wiring connections on them to make sure that they are secure and not incorrectly wired.  

If you have faulty wiring in your vehicle this can cause your electronics or lights to drain energy from your battery even when the vehicle is powered off. This can eventually drain your battery to the level that it can no longer start up your car the next time you go to take it for a drive.  

How To Replace An Alternator

Replacing an alternator on your vehicle is not that hard as long as you can get access to it. On some vehicles, the vehicle manufacturer likes to put the alternator in tough to reach spots such as under the engine or between the engine and an axle. 

If you are lucky like me your alternator will be on top of your engine and will be able to be easily accessed.  You will need a special tool to allow you to easily slide off your serpentine belt from the radiator pulley.  You will also need a basic toolset to allow you to remove the bolts attaching the alternator to your car.

If you wanted to purchase a serpentine belt tool online I’ve included a link to the most popular serpentine belt tool on Amazon that is also pictured below.

If you are curious how difficult it is to replace an alternator I’d recommend checking out my other article that explains step by step how to replace an alternator.

You may also be interested in checking out a Youtube video as it can show the process more in-depth than just reading about how to do it.  I’ve included a video from ChrisFix on Youtube that goes through the whole process.

Related Questions

Can a car run with a bad alternator?  A car can run temporarily with a bad alternator but it may cause your car to stall or die randomly.  If you know that your alternator is bad you should get it replaced because it’s likely to leave you stranded somewhere.

Can a bad battery kill an alternator?  Hooking up a bad battery to an alternator will not kill the alternator. However, a bad battery can cause your alternator to work overtime trying to charge your battery which over time can kill the alternator.  If you know that your battery is bad then you should replace it as it is a critical part of the electrical system of your vehicle.

Can you jumpstart a car with a bad alternator?  Yes, you can jumpstart a car with a bad alternator.  Your battery is used to start up your car. Once your car is started then your alternator kicks in to provide power to the battery to keep your car running. 

If your alternator is going bad but you don’t have the funds to replace it you can buy a trickle charger to charge your battery and that will keep you going for a bit longer but ultimately your alternator will need to be replaced.

How do you know if your starter is bad or your alternator?  If you are having problems starting your car then there may be a problem with your starter or car battery.  If your alternator is not putting out 13.7 to 14.7 volts when your car is running then your alternator is likely bad.

How long does it take to replace an alternator?  Replacing an alternator is not that hard of a job as long as you have easy access to it and will typically take about half an hour to an hour with the right tools.  A lot of cars will have the alternator mounted up high in the engine bay for easy access. If your alternator is mounted underneath your car or in a hard to reach place then it can take much longer than an hour to replace an alternator.

How much does it cost to replace an alternator?

If you’d like to learn more about the costs associated with replacing an alternator check out my other article that breaks down how much it typically costs to replace an alternator depending on the type of car that you have.

How do I know if the battery or alternator is bad?  To tell if your battery or alternator is bad you need to hook up a multimeter to the battery terminals of your car when you have your car running.  You should get a voltage reading of 13.7 to 14.7 volts if your alternator is functioning properly.

If your voltage reading is below or above that range then the alternator needs to be replaced.  Your battery should read about 12.6 volts when your car is not running. If your battery is reading below 12.6 volts that is not a clear sign that your battery is bad. 

Your alternator may just not be putting out enough electricity to keep it charged.  The best way to determine if your car battery is bad is to hook it up to a battery tester to determine that your battery is bad.

Symptoms Of A Bad Alternator – In Conclusion

Hopefully, now you know what the symptoms of a bad alternator are and how you can diagnose a bad alternator.  If you find that your alternator is bad replacing your alternator on your vehicle should not be that tough of a job as long as it is easily accessible. 

If your alternator is in a tough spot where you need to remove parts of your suspension to access then you may want to consider taking your vehicle to a mechanic to have them replace your alternator.