What Are The Symptoms Of A Bad Alternator?

All of us had problems with the car alternator at least once in our life. An alternator has a lifespan of 5-7 years or 80,000 miles. I cannot say for sure how long will your alternator lasts because it depends on various elements like, how much you drive your car, the temperature outside, do you have a garage, etc.

Symptoms of a bad alternator are dim or flickering lights, ignited check engine light, ignited battery warning light, odd noises coming from the alternator, electrical issues, engine stalling, and a dead battery. If your alternator is completely broken your car won’t start because the alternator will drain your car battery and therefore you cannot even start your car.

I had issues with my alternator and changed it twice, so I can say that I am an expert when it comes to bad alternators. Allow me to get into details and explain the seven symptoms of a bad alternator:


What Are The Symptoms Of A Bad Alternator?

Here is a list of the seven most common symptoms of a bad alternator. It is important that you catch these signs at the very beginning to avoid further damage.

1. Dim or flickering lights

A bad car alternator is one of the most common causes of dim or flickering headlights. When an alternator isn’t working properly, it is unable to sufficiently charge the battery, resulting in low voltage that makes headlights significantly dimmer than normal.

Apart from dim or flickering headlights, a bad alternator also causes the backlights to appear weaker than they should. A bad alternator can be a major problem with any vehicle, especially when the lights begin to dim. Nothing is more concerning than hitting the brakes and being met with a faint orange light instead of original brilliance!

Driving with dim headlights is one thing, but driving with dim backlights is another story. Both of these pose a safety concern. The culprit behind the dim and flickering lights is a bad alternator that isn’t capable of charging the battery.

2. Ignited check engine light

If your car doesn’t have a separate warning light for the alternator, it is going to throw the check engine light to alert you of a possible malfunctioning part. When the vehicle’s computer gets information that the alternator isn’t charging properly, it will ignite the check engine light on your dashboard.

On older vehicles, the check engine light is triggered for many reasons. It can be quite hard to determine which caused the check engine light to come on without scanning the vehicle for error codes.

To scan your vehicle for error codes, you will need to hook up an OBD2 scanner to the vehicle’s computer port. Then, you need to start the obd2 scanner and press run. The most common trouble code associated with a bad alternator is P0562 – Charging system voltage low. When the alternator is bad, the power from the battery will be drained excessively, and in return, it won’t get recharged by the alternator. This will most definitely trigger an error code.

3. Ignited battery warning light

When your vehicle’s battery light illuminates, it is very possible that the alternator in your vehicle is having a problem. The alternator is responsible for recharging the battery so if it fails to do its job, then the battery will not have enough juice to power the car’s electrical system and thus the warning light will come on.

An alternator is an essential part of a car’s electrical system. It works by converting mechanical energy into electrical energy and storing it in the car battery. The alternator takes its power from the engine, powering all systems that require electricity such as headlights, radio, GPS, and interior lights. As the speed increases, the alternator is capable of producing more power for other systems such as ACs and winches.

As each system uses some of this stored electrical energy, the battery receives a continual recharge from the alternator to ensure a constant supply of power throughout. Without an alternator working properly, your car will soon be immobilized when the battery runs low on charge, causing the battery warning light to become ignited.

4. Odd noises coming from the alternator

If you hear a grinding noise coming from the alternator, it is an indicator that the bearings are going bad. However, if you hear a squealing noise coming from the alternator, you should check the serpentine belt. A bad serpentine belt has a weak grip and doesn’t rotate the bearings on the alternator. This will give out the same output as a bad alternator.

Bearings are an essential part of any alternator, allowing it to rotate smoothly and efficiently. Alternator bearings provide support for the rotating external components in the alternator, minimizing wear and friction between them. Without these bearings, the entire alternator assembly would be unable to turn efficiently, reducing the overall output of electricity. When the bearings go bad, the alternator will produce grinding noise.

The second noise, the squealing noise comes from a bad serpentine belt. The serpentine belt plays a vital role in the charging system of your car. It’s a major component of the alternator, which is responsible for producing electricity to power all electronic parts of the vehicle.

The belt is made up of Kevlar-reinforced rubber and spins around multiple pulleys connected to components like the alternator, water pump, power steering pump, and air conditioning compressor. As it rotates around these parts, it helps transfer energy generated from the crankshaft to each one, in turn, enabling them to move and produce power accordingly. When the serpentine belt goes bad, you will hear a squealing noise coming from the alternator.

5. Electrical issues

What Are The Symptoms Of A Bad Alternator 2

The alternator is a vital part of modern cars’ electrical systems, as it ensures that the battery and other electrical components are charged while the car is running. It works by converting mechanical energy from the engine into electrical energy to charge the battery. An internal voltage regulator then adjusts this energy output and sends the right amount of electricity to the battery, keeping it within its optimal charging range.

When the alternator goes bad, all the electrically powered components of the vehicle will start to fail. This includes the AC, radio, interior lights, dashboard lights, and other components like charging ports. If your radio starts to turn on and off, make sure to check the alternator first.

6. Engine stalling

What Are The Symptoms Of A Bad Alternator 2

The alternator powers more important components than the AC or the radio. In order for combustion to occur, the engine requires air, fuel, and a spark. Since the fuel supply and the spark plugs are electrically operated, if there is not enough power in the battery, the engine will stall due to a lack of fuel and spark.

When you start the vehicle, the computer draws power from the battery. It might sound simple, but it is not. Combustion is a complex process. In order for the combustion cycle to occur, there should be a recalculated amount of air and fuel. This air and fuel mixture is then ignited by a spark plug. However, none of this can happen without electrical power.

7. Dead battery

What Are The Symptoms Of A Bad Alternator 2

The alternator in a car is essential to its overall operation, as it helps to keep the battery adequately charged. If the alternator isn’t functioning correctly, then the battery will begin to gradually deplete itself of charge and become “dead”.

This can have serious implications for your car’s performance, as you won’t be able to start the engine or power any of its electrical components. There can be many potential causes for a bad alternator – from an absence of lubrication between parts causing them to seize and eventually burn out, to faulty wiring or broken components.

It is important that you get such faults checked out quickly by a qualified auto repair service before it has a chance to wreak even worse havoc on your car.

Will a Car Run With a Bad Alternator?

Depending on how bad the alternator is, your car may or may not run. If your alternator is only just begun to go bad, you may experience weak headlights, the AC and the radio may not come on, and potentially engine stalling from time to time. However, if your alternator is completely bad, you will not be able to start your vehicle at all.

One of the most important questions to answer before starting a car is how much charge a car battery needs. Generally speaking, your car battery needs at least 12 volts of power to start and remain running. Without the required charge, you may experience a slow or sluggish start-up.

So, if your alternator is able to produce 12 volts of charge to the battery, you will be able to start your vehicle. However, when the car is running, it continues to drain the car battery. This is why it is important that the alternator is constantly charging the battery.

How To Diagnose A Bad Alternator?

Diagnosing a bad alternator will require basic tools like a multimeter. You do not have to be an expert to diagnose a bad alternator. Just follow this guide and do not skip a step.

1. Test the battery terminals with the vehicle turned off

In order to test the alternator, you will need a multimeter (alternator testing tool). So, you want to set your multimeter to DC v, which is DC volts, and you want to set it above 15 or 20. You want to make sure your positive and negative battery terminals are clean so that you’ll get a reading when you do this test. Put the black plug on your negative and red on your positive terminal.

You should get a reading of around 12,6. It could be a little bit lower, or a little bit higher. That’s not a big deal, but 12.6 is the magic number to shoot.

2. Test the battery terminals with the vehicle running

Next, start the car, and ideally what should happen is the reading should go between 14.2 and 14.7 volts. That means your alternator is running correctly and charging the battery up correctly. If you’re getting over 14.7 volts, that means that your alternator is overcharging the battery and that could cause damage to the battery, so you don’t want that.

If it’s under 14.2, depending on how much under, let’s just say 13.2, that means your alternator isn’t strongly charging the battery. It’ll still charge it because it’s still above the 12.6 volts, but it’s not going to be enough to charge it when you run accessories such as your headlights or radio.

3. Put on a load to the battery and alternator

Next, while your car is running put on a load to the battery and alternator. Turn on your headlights, radio, and off-road lights (if you have). The readings shouldn’t drop too much. We want to make sure the voltage doesn’t go below 13 volts. If it doesn’t go below 13 volts, your alternator is in great condition.

4. Things to check on before moving to next step

First off you want to check out the connections on the terminals. If there is dirt on your terminals, sand them and get a really good connection. Sometimes the connection isn’t good, and that’ll causes the alternator to have a hard time charging the battery.

Another spot to look at is the back of the alternator. Make sure all the wires are plugged in and secured.

Check for any corrosion or damage to the wires, any frayed wires, or any kinked wires. All that stuff could cause a problem.

Also, your alternator might have an external voltage regulator. Check the wires to the external voltage regulator. Make sure that it’s going there. Make sure it’s clipped in and make sure the external voltage regulator is working.

And finally, as the car is running, make sure that the alternator is spinning. Make sure that the belt is tight. You want to make sure your belt is tight on the alternator because that’s how you get your power.

5. Perform a voltage drop test on the negative battery terminal

This test is for the negative and positive sides of the battery. First, test the voltage drop on the negative side of the battery. Here is how to perform a voltage drop test:

  1. Start the car and turn on a bunch of accessories. You want your headlights on, you want your blower fan on, and your radio on.
  2. Then connect the black lead to the negative side of the battery.
  3. Then touch the red lead to the alternator case. Make sure you have a good connection.
  4. Raise your RPMs to about 1500.

You should see a reading of around 0.5 volts. You don’t want to see a reading that is 1.0 or 2.0 because then you have a problem. If you are getting a 1.0 to 2.0 reading, what you want to do next is take the red lead and touch it to the bracket, and if you see a substantial voltage drop that means the connection between the alternator and alternator bracket needs to be clean because the ground isn’t good.

Now if you don’t find your problem between the connection of the alternator and the alternator bracket, then you should try the engine block. You want to be careful because the fan is running. If you see a substantial decrease in voltage from your alternator case to this then that would be where your problem is. At that point, I would clean the connection between the mounting bracket and the engine block. You can also check your chassis ground.

Remember to bring the RPMs up to about 1500 when you do all these tests. The idea is that keep testing the ground connections until you can find where the connection is bad. Once you find the bad connection sand it and get it clean so that the connection is good and then hopefully that will fix your problem.

6. Perform a voltage drop test on the positive battery terminal

Now we’re gonna test the voltage drop across the alternator and the positive side of the battery. To do this:

  1. Turn on the accessories on the car.
  2. Bring it up to 1500 RPMs.
  3. Connect the red lead to the positive battery terminal and the black lead to the B+ post on the alternator. The B+ post has a nut and a post, so make a connection. Here you should get a reading below 3.0.
  4. The next place you’re gonna want to check is the lead that’s coming from the alternator into the wire. There’s a metal piece between the nut and the red there on the alternator. So just touch it in there and then see the readings.

How Much Does It Cost To Replace An Alternator?

Alternators typically last around 50,000-60,000 miles. So, if you had your car for many years, it is most likely that you will have to change your alternator at some point. So, when the time comes, you want to be informed about the prices of the replacement.

The cost of replacing an alternator depends on several factors, including the make and model of the car it is being installed into and the availability of parts in a particular area.A remanufactured alternator for a domestic car costs about $300-$500. Parts and labor are included. A new alternator is almost double the price $500-$1000.

Factors such as labor costs, quality of the replacement part and any taxes or fees that may apply will all have to be factored into the overall price before repair work begins. It’s important to know how much it costs to replace an alternator ahead of time so you can plan accordingly and ensure that you don’t overspend.

Can You Drive A Car With A Bad Alternator?

This is a great question. It depends on how bad your alternator is. It is certain that you cannot drive very long with a bad alternator. Once you start your car, you can drive your normal distance. The problem occurs when you turn off your car.

Let’s say you stopped to refill your gas tank. If your alternator is bad, you won’t be able to start your car. The reason is that a bad alternator is not recharging your battery while driving, meaning that you will drain your battery while driving and when you stop your battery won’t have enough energy to start the car.

It is not recommended to drive a car with a bad alternator as it can have serious and dangerous repercussions. The alternator is an integral part of the car’s electrical system since it creates electricity necessary for operating various components, including the engine.

Driving with a faulty alternator will cause the vehicle battery to drain quickly, leading to temporary power loss and possibly stalling the engine. Additionally, it could lead to a total failure of all electrical systems in the car.

Why Is My Alternator Not Charging?

There are 5 reasons why your alternator isn’t charging your battery:

  1. Computer error: Most of us drive cars made in the last 20 years. Our cars have a central computer system. This system manages the alternator. All it takes is a small computer error and you will end up with a malfunctioning alternator.
  2. Broken belt: The belt produces the mechanical power that the alternator converts to electrical energy. This belt can easily break or get damaged.
  3. Blown fuse: Some cars have alternators with fuses. These fuses can break from power surges or old age. Check your owner’s manual to see if you have an alternator with a blown fuse.
  4. Wiring issues: There are many wiring components in the alternator. One disconnected wire can cause no power to the vehicle.
  5. Bad alternator: All products have a lifespan. An alternator has a 2-5 year lifespan depending on how much you drive your car.

I hope this article will help you to test your alternator and see if it needs replacement or just some good cleaning.

Is your engine oil due for a change? Visit our Car Fluid Guide Website to learn the importance of changing your oil on time, which type of engine oil is best for your vehicle, and much more.

Bob Semana

Hi there, I am a Mechanical Engineer that specializes in AC, Alternators, Batteries, Cooling systems, and Drive Train issues.

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