Maintenance Tips, Tricks And Hacks For Your Vehicle

10 Symptoms Of A Bad Car Alternator




All of us had problems with the car alternator at least once in our life. An alternator has a lifespan of 5-7 years or 80,000 miles.

I cannot say for sure how long will your alternator lasts because it depends on various elements like, how much you drive your car, the temperature outside, do you have a garage, etc.

I had issues with my alternator and changed it twice, so I can say that I am an expert when it comes to bad alternators. Allow me to get into details and explain the seven symptoms of a bad alternator:

Key Takeaway

  • A car alternator is a device that converts mechanical energy from the engine into electrical energy, which is used to recharge the battery and power the electrical systems in the vehicle while the engine is running.
  • Symptoms of a bad alternator can include dim or overly bright lights, a dead battery, slow or malfunctioning accessories, trouble starting the car, strange noises from the engine, underperforming electrical systems, and warning lights on your dashboard.
  • While a car can technically run with a bad alternator, it is only for a short period of time as the alternator charges the battery when the engine is running; once the battery is depleted due to a faulty alternator, the car will shut down.
  • To diagnose a bad alternator, you can look for symptoms such as dim or flickering lights, battery light on the dashboard, difficulty starting the car, and other electrical issues, but a definitive diagnosis often requires using a multimeter to check the voltage at the battery with the engine running.

What Is a Car Alternator?

A car alternator, a key component of your vehicle’s charging system, is responsible for providing power to the car’s electrical systems and keeping the battery charged. It is essentially an electric generator.

When your vehicle’s engine is running, it turns the alternator, which then converts this mechanical energy into electrical energy. This electricity is used to power systems like the headlights, air conditioning, radio, and other electronic features in the car.

Additionally, the alternator plays a crucial role in recharging the car’s battery. As the battery provides the initial power to start the engine, the alternator ensures the battery stays charged, replenishing any power the battery uses.

10 Symptoms Of A Bad Alternator

Here is a list of the seven most common symptoms of a bad alternator. It is important that you catch these signs at the very beginning to avoid further damage.

Warning light on the dashboard

A warning light on the dashboard, often shaped like a battery, is one of the most common symptoms of a bad alternator. This light is linked to the car’s computer system and is designed to light up when there is an issue with the charging system.

Dim or flickering headlights and tail lights

Dim or flickering headlights or tail lights can indicate a failing alternator. This is because the alternator provides power to these systems, and if it’s not working correctly, the lights may not receive enough power to function properly.

Dead battery even if you just drove your vehicle

If your battery is dead, even though you’ve been driving your vehicle, this could be a symptom of a bad alternator. The alternator is responsible for charging the battery while the engine is running, so if it’s not working correctly, the battery may not charge as it should.

Grinding or whining noises coming from the alternator

Grinding or whining noises coming from the area of the alternator could indicate a problem with the bearings inside the alternator. If these noises are present, it’s best to have the alternator checked out as soon as possible.

A burning rubber smell

A burning rubber smell could be a sign of a bad alternator. This might be due to a belt slipping on the alternator pulley or the alternator overheating, both of which could indicate a problem with the alternator.

Electrical issues such as power seats or windows becoming progressively slower

If electrical components in your car, like power seats or windows, are becoming progressively slower, this could be a symptom of a bad alternator. The alternator supplies power to these systems, and if it’s failing, they may not get the power they need to function correctly.

Difficulty starting the car (starter not engaging)

Difficulty starting the car, or the starter not engaging, could be a sign of a bad alternator. If the alternator isn’t charging the battery properly, there may not be enough power to start the engine.

Frequent jump starts needed

If you find yourself needing to frequently jump-start your car, this could be a symptom of a bad alternator. The alternator should keep the battery charged, and if it’s failing, the battery may frequently run out of charge.

Broken or loose connections around the alternator

Broken or loose connections around the alternator can cause the alternator to work intermittently or not at all. Regularly inspecting and maintaining these connections can help prevent alternator issues.

Vehicle stalling

A vehicle that stalls while running could be experiencing alternator problems. Since the alternator is responsible for providing electrical power to the engine, a malfunctioning alternator could lead to the engine stalling.

Will a Car Run With a Bad Alternator?

Depending on how bad the alternator is, your car may or may not run. If your alternator is only just begun to go bad, you may experience weak headlights, the AC and the radio may not come on, and potentially engine stalling from time to time. However, if your alternator is completely bad, you will not be able to start your vehicle at all.

One of the most important questions to answer before starting a car is how much charge a car battery needs. Generally speaking, your car battery needs at least 12 volts of power to start and remain running. Without the required charge, you may experience a slow or sluggish start-up.

So, if your alternator is able to produce 12 volts of charge to the battery, you will be able to start your vehicle. However, when the car is running, it continues to drain the car battery. This is why it is important that the alternator is constantly charging the battery.

How To Diagnose A Bad Alternator?

Diagnosing a bad alternator will require basic tools like a multimeter. You do not have to be an expert to diagnose a bad alternator. Just follow this guide and do not skip a step.

1. Test the battery terminals with the vehicle turned off

In order to test the alternator, you will need a multimeter (alternator testing tool). So, you want to set your multimeter to DC v, which is DC volts, and you want to set it above 15 or 20. You want to make sure your positive and negative battery terminals are clean so that you’ll get a reading when you do this test. Put the black plug on your negative and red on your positive terminal.

You should get a reading of around 12,6. It could be a little bit lower, or a little bit higher. That’s not a big deal, but 12.6 is the magic number to shoot.

2. Test the battery terminals with the vehicle running

Next, start the car, and ideally what should happen is the reading should go between 14.2 and 14.7 volts. That means your alternator is running correctly and charging the battery up correctly. If you’re getting over 14.7 volts, that means that your alternator is overcharging the battery and that could cause damage to the battery, so you don’t want that.

If it’s under 14.2, depending on how much under, let’s just say 13.2, that means your alternator isn’t strongly charging the battery. It’ll still charge it because it’s still above the 12.6 volts, but it’s not going to be enough to charge it when you run accessories such as your headlights or radio.

3. Put on a load to the battery and alternator

Next, while your car is running put on a load to the battery and alternator. Turn on your headlights, radio, and off-road lights (if you have one). The readings shouldn’t drop too much. We want to make sure the voltage doesn’t go below 13 volts. If it doesn’t go below 13 volts, your alternator is in great condition.

4. Things to check on before moving to the next step

First off you want to check out the connections on the terminals. If there is dirt on your terminals, sand them and get a really good connection. Sometimes the connection isn’t good, and that’ll cause the alternator to have a hard time charging the battery.

Another spot to look at is the back of the alternator. Make sure all the wires are plugged in and secured.

Check for any corrosion or damage to the wires, any frayed wires, or any kinked wires. All that stuff could cause a problem.

Also, your alternator might have an external voltage regulator. Check the wires to the external voltage regulator. Make sure that it’s going there. Make sure it’s clipped in and make sure the external voltage regulator is working.

And finally, as the car is running, make sure that the alternator is spinning. Make sure that the belt is tight. You want to make sure your belt is tight on the alternator because that’s how you get your power says Car Direct.

5. Perform a voltage drop test on the negative battery terminal

This test is for the negative and positive sides of the battery. First, test the voltage drop on the negative side of the battery. Here is how to perform a voltage drop test:

  1. Start the car and turn on a bunch of accessories. You want your headlights on, you want your blower fan on, and your radio on.
  2. Then connect the black lead to the negative side of the battery.
  3. Then touch the red lead to the alternator case. Make sure you have a good connection.
  4. Raise your RPMs to about 1500.

You should see a reading of around 0.5 volts. You don’t want to see a reading that is 1.0 or 2.0 because then you have a problem. If you are getting a 1.0 to 2.0 reading, what you want to do next is take the red lead and touch it to the bracket, and if you see a substantial voltage drop that means the connection between the alternator and alternator bracket needs to be clean because the ground isn’t good.

Now if you don’t find your problem between the connection of the alternator and the alternator bracket, then you should try the engine block. You want to be careful because the fan is running. If you see a substantial decrease in voltage from your alternator case to this then that would be where your problem is. At that point, I would clean the connection between the mounting bracket and the engine block. You can also check your chassis ground.

Remember to bring the RPMs up to about 1500 when you do all these tests. The idea is that keep testing the ground connections until you can find where the connection is bad. Once you find the bad connection sand it and get it clean so that the connection is good and then hopefully that will fix your problem.

6. Perform a voltage drop test on the positive battery terminal

Now we’re gonna test the voltage drop across the alternator and the positive side of the battery. To do this:

  1. Turn on the accessories on the car.
  2. Bring it up to 1500 RPMs.
  3. Connect the red lead to the positive battery terminal and the black lead to the B+ post on the alternator. The B+ post has a nut and a post, so make a connection. Here you should get a reading below 3.0.
  4. The next place you’re gonna want to check is the lead that’s coming from the alternator into the wire. There’s a metal piece between the nut and the red there on the alternator. So just touch it in there and then see the readings.

How Much Does It Cost To Replace An Alternator?

Does The Car Alternator Always Charge The Battery

The cost of replacing an alternator depends on several factors, including the make and model of the car it is being installed into and the availability of parts in a particular area. A remanufactured alternator for a domestic car costs about $300-$500. Parts and labor are included. A new alternator is almost double the price $500-$1000.

Alternators typically last around 50,000-60,000 miles. So, if you had your car for many years, it is most likely that you will have to change your alternator at some point. So, when the time comes, you want to be informed about the prices of the replacement.

Factors such as labor costs, quality of the replacement part, and any taxes or fees that may apply will all have to be factored into the overall price before repair work begins. It’s important to know how much it costs to replace an alternator ahead of time so you can plan accordingly and ensure that you don’t overspend.

Can You Drive A Car With A Bad Alternator?

This is a great question. It depends on how bad your alternator is. It is certain that you cannot drive very long with a bad alternator. Once you start your car, you can drive your normal distance. The problem occurs when you turn off your car.

Let’s say you stopped to refill your gas tank. If your alternator is bad, you won’t be able to start your car. The reason is that a bad alternator is not recharging your battery while driving, meaning that you will drain your battery while driving and when you stop your battery won’t have enough energy to start the car.

It is not recommended to drive a car with a bad alternator as it can have serious and dangerous repercussions. The alternator is an integral part of the car’s electrical system since it creates electricity necessary for operating various components, including the engine.

Driving with a faulty alternator will cause the vehicle battery to drain quickly, leading to temporary power loss and possibly stalling the engine. Additionally, it could lead to a total failure of all electrical systems in the car.

Why Is My Alternator Not Charging?

There are 5 reasons why your alternator isn’t charging your battery:

  1. Computer error: Most of us drive cars made in the last 20 years. Our cars have a central computer system. This system manages the alternator. All it takes is a small computer error and you will end up with a malfunctioning alternator.
  2. Broken belt: The belt produces the mechanical power that the alternator converts to electrical energy. This belt can easily break or get damaged.
  3. Blown fuse: Some cars have alternators with fuses. These fuses can break from power surges or old age. Check your owner’s manual to see if you have an alternator with a blown fuse.
  4. Wiring issues: There are many wiring components in the alternator. One disconnected wire can cause no power to the vehicle.
  5. Bad alternator: All products have a lifespan. An alternator has a 2-5 year lifespan depending on how much you drive your car.


Q: What are the symptoms of a bad alternator?

A: The symptoms of a bad alternator can include dim or flickering lights, a dead battery, starting problems, a battery warning light on the dashboard, and strange sounds coming from the engine.

Q: How do I know if my alternator is failing?

A: If you notice any of the symptoms mentioned earlier, such as dim or flickering lights, a dead battery, or starting problems, it could indicate that your alternator is failing.

Q: What should I do if I suspect a problem with my alternator?

A: If you suspect a problem with your alternator, it is recommended to have it checked by a professional mechanic or auto parts store. They can perform a diagnostic test to determine if your alternator is the culprit.

Q: Can a bad alternator cause my car to stop working?

A: Yes, if your alternator is not functioning properly and is not providing enough power to your car’s electrical system, it can cause your car to stop working.

Q: What causes an alternator to go bad?

A: There are several potential causes for a bad alternator, including a faulty voltage regulator, worn-out bearings, a failing alternator pulley, or simply old age.

Q: How can I recharge my battery if my alternator is not working?

A: If your alternator is not working and your battery is dead, you can try jump-starting your car using jumper cables connected to another vehicle. However, it is important to have your alternator repaired or replaced as soon as possible.

Q: Can bad alternator damage other car components?

A: Yes, a bad alternator can potentially damage other car components, such as the battery, the serpentine belt, or even the car’s electronics.

Q: Can I drive my car with a bad alternator?

A: It is not recommended to drive your car with a bad alternator for an extended period of time. Eventually, the battery will lose its charge and the car will stop running.

Q: How long does it take to replace an alternator?

A: The time it takes to replace an alternator can vary depending on the make and model of your car. It can range from a couple of hours to a full day.

How can I avoid problems with my battery or alternator in the first place?

Preventing issues with your car’s battery or alternator involves consistent maintenance and judicious use of the vehicle’s electrical systems.

This includes regular inspections, keeping the battery clean, limiting short rides, managing electrical load, timely battery replacement, shutting down the vehicle properly, and regular servicing to identify potential issues early.

Following these steps can lengthen the lifespan of your battery and alternator, reducing potential problems and enhancing your vehicle’s reliability.

In Conclusion

In conclusion, a car’s alternator is a crucial component that ensures all electrical systems function optimally.

Recognizing the signs of a faulty alternator can save you from unexpected breakdowns and costly repairs.

These symptoms can range from dashboard warning lights, dim or flickering lights, and unusual noises, to stalling or difficulty starting your vehicle.

Regular maintenance and timely intervention upon noticing these signs can keep your alternator, and by extension, your car, running smoothly.



Vide Polowenski, Senior Mechanic

The information in this article is current and up-to-date in accordance with the latest mechanic SOPs.

Please take the time to leave a comment if this article has helped you in any way, you need additional help, or you have a suggestion.

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