What Are the Symptoms of a Bad Alternator?


If your car has been running rough lately or doesn’t want to start up in the morning, you might be looking at a defective alternator. But until you take your car to the shop for a checkup, it’s hard to know for sure.

The symptoms of a bad alternator may include dim headlights, trouble starting your engine, and malfunctioning accessories. That’s because the alternator is responsible for powering your car’s electrical system. So if it fails, you may begin to notice several electrical problems.

If you suspect your vehicle has an alternator problem, this article can help you rule in or rule out a faulty alternator. I discuss common signs of a bad alternator and other possible issues with similar symptoms. Keep reading to check if any apply to your car.

Symptoms of a Failing Alternator

A car whose alternator isn’t functioning normally will display telltale signs. Identifying them early on can save you time, money, and frustration. Here are common potential problems caused by a failing alternator:

Your Lights Are Flickering and Dimming

The battery supplies power to the car’s electrical components and gets recharged by the alternator. So if the alternator is bad or failing, it might not be able to provide enough power to top up the batter. Consequently, you may notice flickering or dimming lights, from the headlights to the interior lights.

One way to tell if your alternator is healthy is to test its voltage output using a multimeter while the car is running. If it’s lower than 12 volts, you might need a new one. Alternatively, you can check the voltage gauge for voltage fluctuations and output readings that are lower than unusual.

Read: Can You Jumpstart a Car With a Bad Alternator?

Other Causes for Dim Lights

Just because your car is exhibiting this symptom doesn’t mean it has an alternator problem. The battery could be the battery in that it’s not providing enough power to keep things running as they should.

For this reason, you might also want to test the battery voltage when the car isn’t running. If it registers less than 12 volts, there might be a short. It could also mean your car battery won’t hold a charge, which calls for you to replace it.

To know for sure whether it’s an alternator or battery problem causing light dimming in your car, take it to your mechanic for an inspection. After thorough diagnostic testing, they will pinpoint the exact issue with your vehicle’s electrical system.

Read: Car Diagnosis Cost

Your Car Accessories Are Malfunctioning

A bad alternator can make your car accessories act up. If the battery is functioning as expected, but the alternator isn’t providing enough power, you might start experiencing problems with various car accessories.

For example, power windows may take longer than usual to roll up or down. The power sunroof might refuse to close. Your car’s AC could stop cooling properly. Or you may notice your car stereo suddenly cut off and come back on a short while later.

When the alternator fails, it falls on the battery to meet all your car’s electrical needs, including powering the electrical accessories. However, the battery can only do so for a limited time. So if you’re driving and suspect the alternator is failing, turn off all the electrical accessories to ensure the battery power lasts enough to get to a safe place.

Other Causes for Malfunctioning of Car Accessories

Electrical car accessories can still develop faults on their own even if you do everything by the book. It’s a normal part of owning a car.

If a particular feature starts to show signs of an electrical car issue, get your mechanic to check it out. If multiple electrical accessories are malfunctioning simultaneously, it’s probably an alternator-related issue, in which case, you should also have a professional look at the car.

Read: Why Car Won’t Lock or Unlock

Your Engine Is Misfiring

A bad alternator can cause your engine to misfire. And this, in turn, causes your car to start rough idling and affects your fuel economy.

Increased fuel consumption might be one of the first symptoms you notice indicative of potential alternator failure. It’s a consequence of the alternator not supplying power to parts like the fuel injector and ignition coil.

Misfires also cause engine hesitation, where an interruption of continuous power causes acceleration hesitation when you step on the throttle. If your car is experiencing these and other symptoms of engine misfiring, there’s a good chance it’s suffering from alternator failure.

Read: Car Full Service Cost // Whats included?

You Are Having a Hard Time Starting Your Car

If your vehicle has trouble starting, you may have an alternator problem on your hands. It could also be a dying or dead battery causing the issue.

If the reason for your car’s hard start condition is the alternator, it means it’s not adequately recharging the battery. So when you turn the key in the ignition, there’s not enough juice stored in the battery to start the car.

In such a case, use those jumper cables you likely already have in the trunk to jump-start your car. However, if the alternator, and not the battery, is failing, the vehicle will die again shortly after jump-starting it. So you may end up having to call a tow truck to transport it to an auto shop.

If you don’t always carry jumper cables in your vehicles, you should start, especially if you suspect your alternator is going bad. I recommend the Energizer Jumper Cables from Amazon. 

These 6-gauge jumper cables are ideal for basic vehicle types, including sedans, SUVs, and trucks. They’re 16ft (4.88m) long hence easy to reach from one car battery to another. And they come with a carrying bag.

There Are Growling or Whining Noises From Under the Hood

When an alternator is about to give out, you may hear growling or whining noises coming from under the hood. A crankshaft pulley in conjunction with a serpentine belt drives the alternator. If they are not correctly aligned, you’ll hear strange noises, indicating there’s a problem.

Bearings, which support the shaft the alternator pulley spins on, may also be the noise source. When they become too worn out, they start creating grinding noises. In which case, there’s a need for replacement.

It might also be that the alternator components are in good condition, but there’s a loose alternator bolt. Consequently, the alternator moves around as the engine runs, producing noises. An alternator that’s not firmly mounted is not a minor issue as it can lead to failure.

Whatever the reason behind strange alternator sounds, don’t ignore them. Instead, visit the mechanic as soon as possible.

Read: Why Car Won’t Accelerate

There Is a Burning Rubber Smell

The smell of burning rubber could indicate potential alternator trouble. Pulley misalignment or a defective tensioner can cause the alternator’s drive belt (serpentine belt) to slip off the tracks. Consequently, this generates friction between the belt and the accessory drive pulleys, causing the belt to overheat.

The serpentine belt is made of reinforced rubber. So if it overheats, you can smell burning rubber. Normal wear and tear due to constant tension and friction can also cause the belt to produce a burning rubber smell.

Signs of serpentine belt slipping include black marks on the pulleys or smoke rising from the hood. An overworked alternator can also result in a smell like that of an electrical fire, owing to frayed wires.

Odors can signify that your alternator is on its way out. But they’re not always present when an alternator is failing.

In Summary

Total alternator failure isn’t sudden. Signs of potential trouble are usually present beforehand.

If you have multiple issues with your vehicle’s electrical system, for instance, you may have a bad alternator. These include dimming lights, malfunctioning accessories, engine misfiring, and trouble starting the car.

Accompanying these issues may be strange noises and smells that indicate problems with different components of the alternator. If you notice any of these symptoms, get your alternator checked out before you’re stuck on the driveway, or worse, side of the road.

Leave a Comment