March 18, 2021

What Are the Signs of a Bad Alternator?

The alternator plays a major role in your car's electrical system. It helps recharge the battery when the car is in use, and it provides power to the car's features and accessories. If it goes bad, your car won't get the power it needs to function properly.

What Does an Alternator Do in a Car Engine?

An alternator charges the battery when the vehicle is running. It also sends power to the car's electrical system. When the car is driving or idling, the alternator directs power to components such as the headlights, power mirrors, electric steering, power windows, windshield wipers, heated seats, car stereo, and dashboard instruments.

How Long Does an Alternator Last?

An alternator can last up to seven years and 100,000 miles or more. However, it's difficult to make an exact prediction since certain factors can shorten an alternator's life. The alternator provides power for features such as heated seats, the car stereo, and the onboard navigation system, as well as the vehicle's power windows and mirrors. If your car has lots of these types of features and you frequently use them, it could shorten the life of the alternator.

What Are the Signs of a Bad Alternator?

An alternator works with the car's battery to power the vehicle. Since they work in similar roles, the signs of a failing alternator are similar to those shown by a failing battery. If your headlights are dimmer than usual and your accessories are slow or malfunctioning, you could have an alternator problem. If you have a dead battery, it could also indicate that you have a faulty alternator.

Signs of a Bad Battery

Here are some signs of a weak battery:

  • Dim or flickering headlights: Your car's headlights rely on the battery for power. If they flicker, or they're not as bright as they usually are, it could indicate a weak battery
  • Engine slow to crank: If your engine takes longer to crank than it usually does, it could indicate a battery problem.
  • Backfiring: A battery that's near the end of its life can let off sparks. These sparks can cause fuel to accumulate in the cylinders. As this fuel builds up, it can ignite suddenly and with great force, causing your car to backfire.
  • Illuminated "Check Engine" light: If your car's "Check Engine" light comes on, it could indicate a weak battery.
  • Engine doesn't turn over: Does the ignition simply click when you try to start the car, without the engine turning over? This may indicate a battery problem.
  • General electrical issues: Features such as the stereo, power windows, and windshield wipers rely on the battery for power. If some or all these features aren't working as they should, a dying battery could be to blame.

What Does a Bad Alternator Sound Like?

The alternator has a lot of moving parts, and if it's not working properly, those parts may emit strange sounds. If there's a grinding sound under the hood, this could indicate a faulty alternator. This grinding sound is caused by worn-out bearings. If your car makes an odd whining sound, this could also indicate an alternator issue. 

How To Check For a Bad Battery or Alternator

One way to check your alternator involves your car's headlights. You'll need the help of a second person. Start the car and turn on the headlights. Then put the vehicle in "Park." Have the second person observe the car's headlights from outside the vehicle while you depress the throttle. If the car's headlights flicker, dim or brighten when the throttle is pressed, you may be dealing with a faulty alternator.

To check the battery, you can perform what's known as a load test. Again, you'll need the assistance of a second person. Turn on the headlights without starting the engine. Leave the lights on for 15 minutes with the engine off. Then start the car. Have the second person observe the headlights from outside as you start the engine. If the headlights dim as the engine turns over, it could indicate a battery problem.

How To Check the Alternator With a Multimeter

To test an alternator with a multimeter, start by making sure the battery is fully charged. Connect the multimeter's negative lead to the battery's negative post. Then connect the meter's positive lead to the battery's positive post. Adjust the meter to reflect DC voltage using the 20-volt scale, and note the voltage reading. Next, start the car and look at the meter's display. After the car has been on for a couple moments, the display should read at least one volt over the reading you saw with the engine off. If the reading remains the same whether the engine is off or on, it indicates that the alternator isn't generating any electricity.

How Much Is an Alternator Belt?

When the part alone is considered, an alternator belt costs anywhere from $25 to $80. You'll also need to consider labor costs, and these can run anywhere from $75 to $120. The total cost with labor and parts can run from $100 to $200.

If you suspect that you have a faulty battery or alternator, the simplest solution is to take the vehicle to an auto repair shop so it can be inspected by a mechanic.

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