Signs Your Alternator May be Going Bad

You rely on your vehicle just about every day. Conscientious car owners know it's important to maintain a vehicle to get the most out of it. If you pay attention, you can spot clues that parts or entire systems are wearing out or failing. One such part is the alternator, a crucial component in the starting and charging system. If you drive a car for long enough, you may notice signs that the car's alternator is reaching the end of its life. Ignoring these factors can lead to you finding yourself stranded or otherwise unable to use your car, so it’s best to be proactive and replace this part. By heeding the signs of a bad alternator, you can save yourself some stress and a lot of hassles.

The Alternator’s Function

The alternator plays a critical role in the way your vehicle runs. The alternator uses the process of induction to transform mechanical energy into electricity. The alternator’s pulley receives rotational energy from the accessory drive belt, and uses magnetism to generate alternating current, which the alternator then changes intro direct current, which the vehicle can use. With this electricity, the car battery stays charged, powering the vehicle and enabling it to start. The interior lights, headlights, taillights and audio functions of the vehicle work properly thanks to the alternator as well. This part plays such an integral role in your vehicle that its success or failure can have far-reaching consequences on other systems in the car.

What are the Symptoms of a Bad Alternator?

1. The Lights Begin To Dim

When you get into your car at night and need to find something in the interior, it’s nice to rely on the lights. However, if the brightness of these lights begins to wane, you could have a problem with the alternator. Because this part is connected to all electrical components in the vehicle, the interior lights may begin to suffer as the alternator starts to have problems. The dimness may vary depending on how close to dying the alternator may be. Slight dimness indicates that issues are starting, so it’s a good time to check out the alternator and consider replacing it. You may even notice dashboard lights and displays start to dim and get lighter. Headlights may also appear dim when driving at night due to a failing alternator

2. Warning Light Comes On

It’s never a good idea to ignore vehicle warning lights, even though some car owners do. Whether it’s a low oil indicator or a service engine soon light, it’s important to address these needs as soon as possible. Many cars will show a light shaped like a battery on the dashboard display or close to the speedometer. While this can sometimes indicate a battery problem, the car’s computer is telling you that the battery is not fully charged, which can also indicate alternator trouble.

Learn more about why the battery light may be on.

With some vehicles, the warning light for the alternator may be an ALT indicator. When the voltage begins to decrease, different accessories will be affected. For example, if you are using your windshield wipers and radio, power from the alternator may not be sufficient to get the headlights on too, as the alternator is already working too hard to power the other systems.

3. Issues with the Belt

If electrical issues aren’t yet a problem, there could still be other methods for how to tell if alternator is bad. One common cause is a bad belt. Open the hood of your vehicle. If the engine belt is not on correctly or is completely missing, there’s a good chance your alternator is not going to do its job. Some belts may still be in the right spot but may be showing signs of excessive wear, looseness, or there may even be cracks. Replace the belt, and you resolve the alternator’s issues.

4. Unexpected Noises

Car owners are used to hearing strange noises from their vehicles. Different sounds can signify a variety of potential problems. It’s no different with the alternator. Shortly before this part fails, it’s common to hear a growling or whining noise. You may not immediately recognize this sound as a clue that the alternator is going haywire, so it’s important to take the vehicle to a mechanic to investigate the source of strange noises, regardless of what the outcome may be.

5. Flickering Lights

Dim lights are usually an obvious clue to people that the alternator is coming to the end of its life. You may not always experience this situation. Instead, the lights may randomly flicker while you’re driving. This is a clue that the following is happening:

  • The electrical system is giving out.
  • The electrical system is trying to maintain the correct brightness.
  • The alternator isn’t producing enough power to keep the lights going at full strength. 

6. The Battery Died

Many people have experienced the frustration of finding that their car battery is dead. This ordeal can leave you stranded on the side of the road or somewhere far from home. The fact is, the battery might not be the culprit. You could have a new battery working well one day but failing the next because of the alternator. When the alternator stops working properly, the battery will try to compensate by supplying as much power as possible. The battery is able to provide enough power to start the vehicle, but it may not have enough power for long-term use. If your battery stops working, be sure to test the battery and the charging system rather than assuming other issues aren’t causing the failure.

7. Sluggishness

When you open or close the windows or sunroof, or when you’re using the vehicle’s DVD player or stereo, you expect things to work quickly. If it takes longer than usual to perform these functions, the alternator could be the culprit. This would especially be the case if accessories get slower when multiple systems are used simultaneously.

Alternator Resources

Before you head out on your next road trip, learn more about the vehicle’s alternator. You may have asked the question, when should you replace your alternator? These guidelines will help you pay more attention and be aware of proper maintenance and repair needs. Once these issues creep up, don’t wait to address them. You can get the parts you need at your local AutoZone Store. If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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