5 Symptoms of a Bad Alternator (and Replacement Cost)

(Updated on December 29, 2022)

The alternator is an important component of a modern automobile. There are so many electrical systems and components in new vehicles which need to be powered. The alternator is the component which charges these electrical features with power. If it wasn’t for the alternator, there wouldn’t be enough power available to charge these electrical components.

A lot of people forget this important fact and just assume the battery charges everything. The truth is that a car battery only provides the electric current needed for the starter motor to start the engine. Once that happens, the alternator takes over and supplies power to all the electrical systems. It powers things like the headlights, air conditioner, power windows, radio, and so on.

More importantly, the alternator powers the engine and engine control unit as well. Remember, modern vehicles have electrical components in just about every area of the car. All the sensors and computers which exist in a vehicle run on electricity. This is power in which the alternator provides them.

How an Alternator Works

A car alternator works by using mechanical energy to generate electrical energy. It does this by utilizing a belt-driven pulley to turn a rotor inside a stationary set of coils.

As the rotor turns, it generates an alternating current (AC) in the coils. This AC current is then converted to direct current (DC) using a rectifier and is used to charge the car’s battery and power the car’s electrical components.

The alternator powers most of a car’s electronic components while the engine is running, including the headlights, dashboard instruments, power windows, power steering, windshield wipers, heated seats, climate control, and stereo.

It supplies all of these systems with DC power. In addition, the alternator is responsible for charging the car’s battery while driving.

Common Bad Alternator Symptoms

Like a battery, the alternator slowly wears out over time. The more you use your vehicle, the more worn out the alternator becomes. The lifespan of an alternator in newer vehicles is typically anywhere from 6 to 8 years for most people.

You never know when your alternator is going to go bad, but there are warning signs that you can look out for. It is easy to confuse these warning signs with the signs of low battery power. That is why we’re going to outline the specific symptoms of a bad alternator.

1) Dimming Headlights

If you’re driving at nighttime with your headlights on and you notice the headlights starting to dim, then it means your alternator is going bad. The alternator is the main power source of the headlights, so do not think it is your battery that is going bad.

You should immediately stop driving until it is daytime again just to be safe. Then take your vehicle to an auto repair shop and have them replace the alternator.

2) Car Won’t Start

When the alternator goes bad, all the electrical components of the vehicle will draw power from the car battery. Even if your car battery is new, your vehicle won’t make it around the block if the battery is the only thing powering its electrical components.

All the power gets drained out of the battery when there is a bad alternator. As a result, the battery won’t be able to provide an electric current to the starter motor when you try to start your engine. That means your car won’t start.

3) Warning Light

A warning light will illuminate on your dashboard. You should see the letters “ALT” light up to indicate that the alternator is the problem. Although, some vehicles have the letters “GEN” instead.

You’ll most definitely see the battery warning light come on because of the alternator’s effect on it.

4) Electrical Components Stop Working

Since the alternator provides power to the electrical components of the vehicle, you may notice these components are not working so well. For instance, if the air conditioning is failing to blow out air or the radio doesn’t turn on, these would be indicators of a bad alternator.

5) Weird Noises

The alternator has a lot of spinning components inside of it. These components produce the necessary electric current to power all the other electrical components of the vehicle.

As the alternator goes bad, some of its own spinning parts may get damaged or worn. This will cause them to make weird grinding noises. They may also be whining noises too.

Alternator Replacement Cost

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The best option you can do with a bad alternator is to replace it with a new or used one. A new alternator will cost between $400 and $1000. If you purchase a refurbished or re-manufactured alternator, it will cost between $200 and $500.

Whether you go new or refurbished, plan on an additional $100 to $250 in labor to replace the alternator.

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