Alternator Is Bad Or Good How To Know

How To Know If Alternator Is Bad

If you’re dealing with alternators, you must learn how to know if alternator is bad. Most vehicles today make use of two different power sources: mechanical and electrical. A vehicle’s engine generates mechanical force through combustion. Meanwhile, other parts of the vehicle (headlights, radio, etc) rely on electrical power provided by the battery. These two systems interact when an alternator is working correctly. Here, I will discuss how to know if the alternator is bad. This article gives you a closer look at the symptoms of a failed alternator. Let’s learn more about how to know if alternator is bad in-depth.

How To Know If Alternator Is Bad?

Over here, I will explain how to know if alternator is bad.

  1. Dead Battery

When an alternator is not functioning properly, the vehicle uses up all the battery leaving it drained. We all know car batteries are not designed for long-term power use. But a bad alternator won’t charge the battery when the engine is running.

  1. Malfunctioning Accessories

Alternators that aren’t supplying enough power to your vehicle’s electronics often result in malfunctioning accessories. For instance, the windows take longer than usual to roll up/down and other instruments stop working normally. This clearly indicates that you may have an alternator problem.

  1. Whining Noises

Cars that make growling or whining noises can indicate a serious mechanical problem. This sound usually occurs when the belt that turns the alternator’s pulley becomes misaligned or rubs against the side of the pulley.

Keep on reading further to learn how to know if alternator is bad.

  1. Fluctuating Interior Lights

An alternator powers your car’s electrical system. One of the most common signs of a failing alternator is an electrical failure! When you notice that the interior lights are dimming or becoming unusually bright, there is an issue with the alternator.

  1. Dim Or Overly Bright Lights

Similarly, you might notice that your car’s headlights run brighter as you accelerate and dim as you stop. This is a sign that your vehicle’s alternator has trouble delivering consistent voltage to your electronic accessories.

You can keep on reading to learn how to know if alternator is bad on diesel.

  1. Trouble Starting The Engine

Are you having trouble starting your engine? This might mean that your alternator is failing to charge the battery. You might hear a clicking sound instead of a normal engine sound when you turn the key in the ignition.

  1. Engine Stop Running Frequently

If your vehicle stops almost immediately after a jump-start, then your vehicle’s alternator is likely the root cause! Frequent engine stalling (stopping) while driving would point to an alternator problem too. The vehicle’s spark plugs aren’t getting enough power from the alternator to keep the engine running.

If you’ve got an old car, keep on reading to learn how to know if alternator is bad to use the vehicle again.

  1. Foul Odour Of Burning Rubber Or Wires

You may get a foul smell of burning rubber or wires when the parts of your alternator are starting to wear out. This is because the alternator’s drive belt is under constant tension and friction. It may wear out over time and emit an unpleasant burning rubber/wire smell.

  1. Battery Warning Alert

Most people mistake the battery warning light pop-up on the dashboard as a battery-related issue. Sometimes, the battery warning light indicates that there can be a problem within the car’s electrical system including the alternator. The battery warning alert will appear if the alternator is failing or exceeding its voltage limit.

You can keep on reading further if you want to learn how to test alternators.

Test Alternator With Multimeter

Have you ever wondered, how to test if alternator is bad with a multimeter? A multimeter is widely used for determining the amount of voltage in an electrical circuit. It also measures a variety of things including current, continuity, and resistance.

You can follow the below steps to learn how to know if alternator is bad with a multimeter.

  1. Take a multimeter and set it to DCV above 15.
  2. Now, check whether your alternator’s positive and negative terminals are clean.
  3. Place the multimeter’s black cable on the negative terminal.
  4. Then, place the multimeter’s red cable on the positive terminal.
  5. Check if the alternator reading on the multimeter is around 12.6.
  6. When the reading is over 14.7, the battery is overcharged.
  7. When the reading is under 14.7, the alternator is undercharging the battery.

You can even turn on the lights, radio, fan, and other electronics to see if the multimeter reading goes below 13. Also, check if the multimeter reading is above 12.6 when you shut off the car.

Now, how to tell if alternator is draining the battery? Simply open the hood and start your car. While the engine is running, remove the negative cable from the battery to check if the vehicle stalls or dies. 

Can You Jumpstart A Car With A Bad Alternator?

Yes, you can definitely jumpstart your car with a bad alternator. Your car will keep running for some time as long as you have a good battery. A car can run on the battery even if the alternator is bad and not producing the required voltage.

What Can Damage An Alternator?

An alternator can get easily damaged by using the jumper cable wrong, overloading the charging system, and leaking fluid. A tight belt can also damage an alternator.

You can keep on reading to check out how to know if alternator is bad or the battery.

Signs Of Bad Battery

Till now, I hope you’ve understood how to know if alternator is bad. In this section, I will tell you six common symptoms of a dead battery.

  • Dashboard Lights Turn Dim

Usually, the battery gives a charge to the vehicle even when it is turned off. If you notice the dashboard lights are dim, there might be a problem with your battery. 

  • Check For Battery Corrosion

If you are unable to restart your car, then there might be some corrosion on the battery. Sometimes, the alternator does its job of keeping the battery working while the motor is running. The battery won’t retain the charge once the alternator stops.

  • Car Battery Is Old 

Car batteries become less functional as they age. On average, car batteries only last for 3 to 5 years.  After a certain point, the battery can’t hold enough power to start the car. They can’t retain a charge because the metal inside the battery is damaged.

  • Radio Won’t Function Properly 

When you are running the motor, the battery should be able to run electronic components like the radio. If you notice that your radio is not working, there is a possibility your battery isn’t well charged.

  • Car Starts And Dies Immediately

Your car might stop or die immediately when the battery only has voltage to start the car. This is an odd problem that occurs only on certain vehicles.

  • Battery Is Swollen 

You can easily identify a bad battery when it is bloated in the battery’s casing. This problem usually arises when the alternator has overcharged the battery.

You can perform a simple test if you want to know how to know if alternator is bad or battery. If your vehicle jump-starts and keep running, but can’t start again on its own power, a dead battery is the main problem.


How Do You Check If Your Alternator Is Bad?

First, open the hood and start the car. While the engine is running, remove the negative cable from the battery. If the vehicle stalls or dies, the alternator is likely bad.

What Is The Main Symptom Of A Bad Alternator?

Dim Lights. An early warning sign that your alternator is going bad could be dim, flickering lights. This symptom could show up on any or all of your dashboard lights, reading lights, headlights or other lights. The alternator is supposed to provide the electricity for your car’s lights.

How Do You Tell If Its Your Alternator Or Your Battery?

If the engine starts but dies immediately, your alternator probably isn’t keeping your battery charged. If a jump starts and keeps your car running, but the car can’t start again off of its own power, a dead battery is probably your answer.

Can A Car Run With A Bad Alternator?

Can a car run with a bad alternator? Yes. However, a car will only be able to run on a bad alternator for a short period of time. Since the alternator is responsible for charging the battery when the engine is running, once the battery is drained, the vehicle won’t start.

What Destroys A Car Alternator?

There are several issues that can ruin an alternator: Using jumper cables wrong, Overloading the charging system with too many accessories, Leaking fluid, or. A tight belt that can damage bearings.

Will A Car Run With A Bad Alternator?

Can Your Car Run with a Bad Alternator? A car can only run for a very short time with a failed alternator. This is because the alternator charges the battery when the engine is running. Once the battery is depleted, the vehicle will die and fail to restart.

How Do You Know If You Need A New Alternator?

An alternator that is failing doesn’t meet your car’s electrical needs. This could cause your headlights to flicker or go from dim to bright. The alternator is not generating enough power to keep the lights on consistently. It will also affect your dashboard lights, and in some instances, they will even stop working.

Why Do Alternators Fail?

Your car’s alternator may fail for various reasons: Age and use-related wear is often the reason behind a dying alternator. Engine oil or power steering fluid leaking onto the car alternator can lead to its failure. Prolonged idling while using multiple electrical accessories can prematurely wear the alternator.

 Is There A Battery Trick To Test Alternator?

Use a voltmeter to check your alternator; rev your engine to 2000 RPM, keep the engine running, and test the battery with the voltmeter. If your voltage goes from ~12.2 V to ~13-14.5 V, your alternator is doing well. If your V stays the same or decreases, that’s a bad sign.


In the above post, I’ve discussed how to know if alternator is bad or battery. A wide range of problems may arise when an alternator stops working correctly. A failing or bad alternator has trouble charging the battery. Thus, the battery won’t have enough power to start the vehicle. Bad alternators sound like someone is growling or whining! You may get a foul smell of burning rubber or wires when the parts of your alternator are starting to wear out. Several issues can ruin an alternator including leaking fluids. You can now easily identify your car problems by learning how to know if alternator is bad.