How to Tell If Your Alternator Is Bad

The alternator on your vehicle serves a very important purpose. Its job is to recycle the power produced by your car battery as you drive. This will replenish its own power as well as many other electrical components that are being depleted with use. Your battery has a tough job having to put out a lot of energy to supply your vehicle with enough power to get it up and running and keep it that way. Due to the amount of power needed, it would quickly run out of its reserve if the alternator was not there to help replenish it. Many things rely on the alternator to be working at peak performance. When it malfunctions or fails completely, it can possibly cause serious effects that lead to expensive repairs and even the inability to use your vehicle. This article will give you a list of things to watch for so that you will know how to tell if alternator is bad.

Signs of a Bad Alternator

Sign 1: Headlights

One simple sign to watch for that does not necessitate the use of any supplies or special tools, is to look at your headlights. If you notice that they seem quite dim, it could be an indication that your alternator is not providing enough power and could need to be checked out for possible issues. How to test your headlights:

  1. Get into your vehicle.
  2. Start your engine.
  3. Turn on your headlights.
  4. Press the gas pedal. If you see the lights dim as you press the pedal, your alternator is having a hard time keeping up with the demand for power.

Sign 2: Test Using Your Battery

Things You Need

  • Voltmeter
  • Safety Gloves

The Steps

  1. The first step of how to tell if your alternator is bad is to put on a pair of safety gloves. It is important to protect yourself while working with electricity and electrical components.
  2. With your vehicle off, open and secure the hood.
  3. Attach your voltmeter to the battery with the red lead placed onto the positive battery post and the black lead placed onto the ground post of the battery.
  4. Take a reading. It should be at least 12.2 volts. Anything below that and it will not be able to send enough power to the alternator so it can be tested.
  5. Next, start your car and press the gas to 2000 RPMs. This should kick in the alternator and get it working.
  6. Get back to your battery for another reading. The added power should now cause your voltmeter to have a fluctuating readout that sits between 13 and 14.5 volts. This will indicate that your alternator is working correctly and sending enough power to the battery.
  7. Repeat this process after turning on electrical components such as a radio, DVD player, lights, and air conditioner. If the reading remains above 13, then your alternator is able to keep up with the power demand and is working well.

Sign 2: Warning Lights

When your alternator begins to fail, most vehicles will illuminate a warning light on your dashboard. This is an easy indication of how to tell if your alternator is bad. More than likely the light will look like a battery. However, some vehicles have a light specifically for the alternator that looks like “alt” or even “gen.” It may pop on only when the draw is too much for the alternator to handle and shut off once some components have been shut off and reduced power usage. You should not ignore this light even if it only intermittently turns on while you look for ways to tell of how to tell if your alternator is bad.

Sign 3: Battery Check

An alternator can only function as well as your battery. Eventually, your battery will need to be replaced because its life is finite. Thus, it needs to have enough life in it to accept a charge from the alternator. If the battery is weak, the alternator cannot help bring it back to life. To check the battery while you learn how to tell if your alternator is bad, follow these steps.

The Steps

  1. Take your alternator to get an external charge. If you do not have the ability to do this at home, many auto parts stores will charge it for free.
  2. Replace the battery and restart the vehicle. If it will run the vehicle but you notice your lights dim after a short time, you need a new battery. If it fails to, or has a hard time starting the vehicle, a new alternator is needed.

Sign 4: Strange Smells

Alternators help power components that turn belt systems. If the alternator is not working correctly, a belt may be prevented from turning freely. The excess amount of friction will cause the belt to heat up and begin to melt. This will release a burning rubber smell. A burning electrical smell may be caused by the belt on the alternator to slip resulting in poor output. If the smell comes back after tightening your belts, it could indicate a malfunctioning alternator.

Sign 5: Weird Sounds

The alternator has many different parts within it that spin in order to help create the electrical current. Once those pieces have become worn or fail, you may hear a whine or grinding coming from the alternator. Bearings and bushings are usually the first to go and are culprits for making these noises. Unfortunately, if that is the case, you need to replace the entire alternator because it comes as an assembly.


The alternator in a vehicle needs to be in tip-top condition to keep your vehicle functioning. It is responsible for keeping power supplied to the battery so that it can meet the needs of the electrical demands of your vehicle. You might have noticed this if you happened to learn how to jump a car battery without another car. If you are looking for an answer to, how to tell if your alternator is bad, this article outlines some things to look at and look for in order to get you back on the road safely.

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