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10 Signs Of A Bad Alternator – How do I know if I have a bad alternator? 

How To Tell If Your Car Has a Bad Alternator

Although your vehicle's alternator is a small component, it has a very critical role in most gasoline-powered vehicles. Like other mechanical components, the alternator can go bad due to wear and tear over time of usage.

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In this article, we will highlight the top ten signs of a bad alternator along with answering the most frequent questions associated with alternator issues.

What does the alternator do?


Many people believe that the car's battery is responsible for producing the electricity needed to run the vehicle. However, the battery is only used to provide the electricity needed to start the motor.

On the other hand, the alternator, or what is known as the generator, produces the energy needed to keep the car moving and feed the electrical system, including the battery. 

The alternator works exactly like the hydroelectric power generated in the waterfalls. When the engine spins, the crank wheel of the alternator converts the mechanical energy into electrical energy that is used to feed the vehicle and keep the battery fully charged.

That being said, electric vehicles do not have an alternator since they are running by a combination of an electric motor and a battery that produces the energy needed during normal operations. On the other hand, hybrid vehicles do you have alternators, but these alternators do not play the same role as in the gasoline-powered engines. This is because hybrid vehicles use regenerated breaking to provide additional electricity to the battery. 

How do you tell if it's your alternator or your battery? 


Since the battery and the alternator work closely with each other, and if one of them goes bad, the whole electrical system will not function. The question then, when the electrical system goes bad, is it the alternator or the battery?

Luckily, this question can be easily answered by doing a quick jump start. When you do that jump, start to the dead vehicle; if the car started running, then the problem is with the battery, and it must be replaced. On the other hand, if the car did not start after performing a jump start, then its the alternator, and it must be replaced. 

Ten Signs of a bad alternator 


In this section, we will cover the ten top signs of a bad alternator.


  • The car is warning dash light will illuminate 



Your vehicle's internal computer uses warning lights to indicate internal issues with your car. One of the new warning lights that were added within the last decade is a battery-like warning light. While some people may think this warning light indicates issues with the vehicle battery, this is not the case.

The battery-like warning light indicates issues with the vehicles alternator. This warning light will illuminate when the outage voltage of the alternator is below or above a certain preset limit. Once the voltage output is back with the required range, this warning light will turn off.

The alternator's voltage output difference between vehicles and the best place to get information about the expected voltage output for a certain alternator is the vehicle's owner manual. In older vehicles, you might not find the word “alternator” in the vehicle's owner's manual since it was called a “generator.” So, in your vehicle's owner's manual, look for the preset limit of the generator or the alternator to confirm the expected voltage outputs.

In general, most vehicle alternators are expected to generate between 13 to 14.5 volts. These alternators try to maintain a constant voltage output within the specified range. Now, try to start the headlights, use the windshield wipers, turn on your heated seats, and use the rear window defroster at the same time. The alternator might not be able to provide the demand needed to operate all of these accessories at the same time. That's when the alternator warning lights might come on, and this makes a lot of sense as the alternator's output is continuously used by these accessories, which could put the generator's output below the preset limit.  


  • Frequent dimming or extreme brightness in the headlights  



As we mentioned earlier, the alternator produces the energy needed to maintain all electrical accessories functioning. When the alternator goes bad, you will start noticing the effects on these electrical features, including the heated seats, the radio, headlights, etc. Depending on the alternator's problem severity, the range of problems could start from slight flickering in the headlights to extreme headlights brightness or dimming.

In newer vehicles, the vehicles are programs in a way that accounts for situations where the alternator goes bad. These newer vehicles might be programmed in a way that creates a priority list of where the energy should go to and where it should not when there is no sufficient voltage coming out of the alternator. For example, when the alternator goes bad, you will start seeing the symptoms on secondary features like the heated seats or the radial but not the headlights. This is because the pre-programmed vehicles prioritize the headlights to provide you the time necessary to pull over, stop your vehicle, and check the alternator's problem. In other words, electrical supply prioritization comes from safety considerations. 


  • Frequent dimming or extreme brightness in the headlights  



As we mentioned earlier, the alternator could cause problems to your vehicle's headlights, but other parts of your electrical system can also cause headlights problems. To pinpoint the actual problem causing your headlights trouble, you need to notice the headlights pattern. If your headlights are dimming, then brightening than dimming back, this indicates an issue with your electrical system that could be your alternator or not. However, if you're headlights are dimming in response to electricity demand withdrawal, then it's your alternate. 

For example, if you noticed that your headlights are dimming when you try to turn on your radio or use your heating seats, this indicates that there is some electricity withdrawal by other electrical components, and that is a direct sign of the alternator not providing the required voltage.

Thus, always keep an eye on the headlights pattern to narrow down the causes for your issues. 


  • A dead battery 



A dead battery is not always related to the alternator; however, a bad alternator could result in killing your battery to grab your attention. 

In vehicles, batteries are not designed to supply electrical power for a long time. Your vehicle's battery produces the required electricity needed to start the motor.

Part of the alternator's job is to keep your battery fully charged. That's why, when your alternator goes bad, your battery will run out of electricity eventually.

Therefore, if your battery goes dead, you need to ask yourself the question of why is it dead in the first place? Is it a problem with the alternator or with the battery itself? 


  • The alternator's electricity is not going anywhere 



The alternator sends the electricity to the different electrical components through wires or cables. If there are problems with the wires or these cables, even if the alternator doesn't have any problem, the electrical system will not function.

The best way to diagnose wires' issues is by monitoring the headlights pattern. If you see the headlights are brightening extremely, this indicates that the alternator is trying to produce more energy to overcome the resistance in the broken wires, and so this gets reflected on the power of the headlight. 


  • Loose alternator's belt  



Another reason for a bad alternator is it broken or loose alternator belt. Even if you are not an experienced or skilled mechanic, you can still open the hood and look for hanging, broken, or missing alternator belt.

It is recommended that you perform a regular check for your alternator belt. Make sure that your vehicle cools down before you perform any checks. Open the hood and look for age signs on your alternator's belt. For example, if you see that your alternator belt is cracked or have extensive wear, this is an indication of near future alternator's problem. Keep in mind that you are alternators belts have to be at the proper tension, and a lot of tension is not a good thing as well.  


  • Weird sounds coming from your alternator 



If you were not able to visually detect the alternator's problem, weird noises could be your second clue. In general, a rule of thumb, if you hear any strange noises in your vehicle, is an indication of an internal problem. This problem could be as simple as an easy fix or as severe as complete engine failure.

Therefore, it is recommended that every time you hear weird noises in your vehicle to take it immediately to the repair shop to avoid higher repair costs.

A lot of people who had issues with their alternator complained hearing growling or whining noise due to issues with the pulley not being aligned with the alternator's belt. Therefore, if you heard such noises, and this noise is associated with additional issues with the electrical system, it could be your alternator. 

The best way to confirm is to take your vehicle to the mechanic and report the type of noises you heard so he can best help you.


  • Weird sounds coming from your alternator 



The third way to check for alternator's problems is by checking for weird smells. In the automobile world, any weird smell can indicate internal issues with your vehicle; these smells do not have to be bad all the time.

If you smell burning rubber, this indicates that your rubber belt of the alternator is overheating and having some problem that could lead to near-future alternator failure. 

If you also smelled some electrical fire, this indicates wires overheating as your alternator tries to push more power to overcome the wires' friction. 


  • The vehicle takes time to accelerate 



Slow acceleration can be an indication of multiple or different problems in your vehicle. If you notice that your vehicle is not accelerating properly along with other electrical issues, this is an indication of issues with your vehicle's excellent alternator.

Therefore, several electrical problems at the same time is not a coincidence. You need to take your vehicle to the mechanic and try to limit your electrical voltage usage as much as you can until you get to the repair shop to check what's going on with your alternator.


  • Stalling issues and difficulty starting  



The last sign of bad also nature we would like to highlight here has to deal with vehicles stalling and not starting properly. If you were not able to start your vehicle, this indicates that your battery is dead or could be your alternator is not functioning. 

As we mentioned before, you can perform a quick jump start to your vehicle and confirm that it's your alternator or not your battery. 

FAQ about signs of a bad alternator 



  • Can you drive a car with a bad alternator? 



Since the alternator is responsible for providing the required energy needed for all electrical components to function, you can run your vehicle with a bad alternator for a very short period but, don't be surprised to have your vehicles shut down suddenly. 

Therefore, if your alternator is not functioning properly, never try to run your vehicle; instead, try to minimize the voltage usage as much as you can. 


  • Will AutoZone change the alternator? 



AutoZone doesn't perform alternator replacement. On the other hand, if you can take out your alternator for them to test it, they can do that for you. 

In general, changing the alternator should be an easy fix for many people to do it their selves even if they don't have an advanced mechanical skill set. 


  • How long can a car run without an alternator? 



Once the alternator is not functioning, your vehicle will rely primarily on the battery for electricity. Therefore, your vehicle will keep running until your battery is dead, which ranges between 5 to 30 minutes, depending on your battery's capability. 


  • What causes an alternator to fail? 



One of the common causes of alternator failure is a leaking diode. Diodes are a vehicle component that converts the AC output of the alternator into DC.


  • Will the alternator kill a new battery? 



The short answer is, ‎” Yes.” A bad alternator will result in killing your new battery; simply because the vehicle will not have the electrical power necessary to function the electrical components. 

Therefore, the vehicle will start consuming your new battery's energy. If this happens continuously, it is not surprising that you wake up in the morning and find you a new battery dead. 

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