Last Updated: 26.11.2021

It all starts with minor issues that are easy to ignore—a dimmed headlight, maybe a dash light that comes on for a short while before disappearing, and flickering gauges. Think back for a moment and ask yourself: have you noticed an odd smell, dimming lamps, or heard a growling sound from the hood? 

When these signs appear, you might wonder what exactly is happening to your car. Well, these are possible signs of a bad alternator, and if not addressed immediately, it could escalate to bigger problems, from a slow start to a dead engine. That’s certainly something you don’t want to happen. 

Keep reading as we delve deeper into your car alternator, demystifying how it works and highlighting signs that indicate it might be faulty. 

How Does an Alternator Work?

An alternator is a car generator designed to generate electricity, distribute it to different parts, and charge the battery. Apart from the modern hybrid cars, all other cars that use a standard internal combustion system will have an alternator under the hood. 

So, how does it work? Let’s start by understanding the main parts of an alternator: 

  • Rotor
  • Stator
  • Brush holder
  • Rectifier 
  • Pulley

exploded view of alternator

The process of electricity generation starts with the engine. In many cars, the alternator is connected to the crankshaft with a belt. When spun at high speed, the alternator’s rotors generate electricity. Then, magnets around the rotor rotate around copper wires to create a magnetic field. 

The magnetic field generates energy (voltage) that is captured by the stator. Then, this energy is directed to the vehicle’s regulator which distributes it to the vehicle’s accessories and which also manages the battery’s voltage.

There is one more thing you need to know. Since your car battery uses a one-way direct current (DC) current, the electricity from the alternator (alternating current) cannot be used to recharge it directly. It would not work. Instead, it is passed via a diode rectifier that converts the AC from the alternator to DC. 

10 Signs of a Bad Alternator and Corrective Measures

If you find your car with any of the following issues, chances are that it has a problem with the alternator. So, let’s look at them, starting with the most common ones.

Warning Lights

Most vehicles, especially those designed in the last decade, have a warning light to indicate if the alternator has an issue. It is shaped like a battery, although it is possible for some to have “GEN” or “ALT,” meaning generator or alternator, respectively. 

Some drivers, when they see the light, tend to think that it is the battery that is faulty, but that is wrong. The issue is with the alternator.

warning lights on dashboard

The light works with the vehicle monitoring system and will signal you when the alternator’s voltage output is lower or higher than the preset levels. If the voltage output is within the range, the light remains unlit. When alternator problems begin, you may notice the light coming on for a few seconds and then off.

Most alternators deliver 13-14.5 volts and they will always try to maintain a constant level. When the car needs more power, especially when the headlights, heated seats, and windows defroster, among other accessories, are on, the alternator needs to work harder to maintain a constant voltage output. 

The warning light is likely to come on if it is not working to its full potential when the demand is high. Then it goes off.

Dim Lights

A failing alternator can create electrical issues in your car, resulting in erratic headlamps, such as extreme brightness or dimming. 

Because the alternator supplies your car with its electrical needs, all the accessories that rely on it are likely to experience issues if it is faulty. Dash lights and headlamps might dim, while others, such as tachometers and speedometers, may stop working.

With dim lights, it is important to note that the issue depends on several factors. The first is how effectively your car’s alternator is generating electricity and its position in the death cycle. Indeed, the death cycle is how most cars are programmed. Auto manufacturers set cars with a list of priorities so that specific areas are prioritized in the event of an alternator problem. 

For example, the car might turn off the radio before the headlights dim. This is justifiable because you will need better visibility when pulling over and stopping your vehicle. The radio and heated seats, among other accessories, are, therefore, considered secondary.

Loose Connection

Let’s put it this way, you have checked everything else, from belts to the lamps, and there seems to be no problem, but the battery is dead. Also, other electrical pieces of equipment of the vehicle are okay. This can only mean two things; your car’s alternator is producing electricity but not getting everywhere, or it is the wrong type.

alternator and fusebox on engine

Because electricity from the alternator is run through thick cables, problems with the connections can easily stop or reduce the flow. Often, a problem of this nature might cause dazzling light because your car’s alternator generates more electricity to help overcome the prevailing resistance. 

Another symptom of a loose or broken connection issue is the smell of hot wires. Because of high resistance in the wires, heat is generated in the same way a stove heats through resistance. This smell is likely to be stronger when you open the hood. 

Because a car alternator charges the battery through a diode rectifier, it might also be the cause of the dead battery. So, is the rectifier efficiently converting AC current from the alternator to DC that the battery can take? If it is not, the battery is likely to die sooner than later. 

Dead Battery 

Although a dead battery is not an alternator-related issue, starting failures point at a possible challenge with the starting system. 

When you turn on the ignition keys in your car, does it give a cranking sound of relays but does not start? If you try several times and even the relays go dead, the problem is likely to be a dead battery. However, let’s ask another question, “why exactly is the battery dead?”

car battery image red positive terminal

If your car’s alternator fails, the battery steps in and starts operating as a capacitor to power different systems. Because it is not getting enough or any recharge from the alternator, it will be unable to support the starting system, which requires a lot of energy to produce a spark for internal combustion. 

When dealing with car batteries, it is also crucial to be extra careful because every battery will ultimately fail. So, even if the alternator can cause a dead battery, other issues such as rapid discharge, nearing the end of life, or damaged terminals can also kill it. 

Make sure to have both the alternator and battery checked by an expert to confirm the actual cause of the problem. 

Flickering Lights

We mentioned earlier that a faulty alternator causes dimming of both interior and exterior lights. But, that is not all. 

Even if your lights are not dimmed, check them closely to see whether they are flickering. You are likely to find dimming and flickering going hand in hand, but they can also happen separately. 

So, here is the catch. If you find the lights dimming, then dull and back to bright again, the electrical system, no doubt, has a problem, and the alternator is the first suspect. Why the alternator? 

Expert mechanics will point their fingers at the alternator because its work is not just to generate electricity, but also to maintain it at a stable level. So, if you notice the flickering lights, the alternator is likely to be trying and failing to maintain the voltage levels demanded by the car. 

To be sure that it is the alternator that is faulty and not anything else, you only need to check whether there is a pattern. For example, do lights flicker when trying to do something that draws a lot of energy, such as turning on the radio or using power windows? If such a pattern is noted, it implies that the alternator of your car might be failing. 

Bad Belts

Ask any mechanic, and they will likely tell you that some people come complaining about their alternator issues, only to realize they have missing belts. In other cases, the belts might have jumped off the sprockets and are hanging there and flapping in the engine compartment. 

Because a damaged belt is pretty easy to see, you only need to check under the hood to notice. This is a problem that you can fix if you have some basic mechanics. Just remember that you need to let the car cool off before trying to fix anything. 

Some of the main issues with alternator belts include: 

  • Cracked belts
  • Excessive wear
  • Loose belts
  • Excessive tension

Note that even if you fixed the belt, it is still important to ask your mechanic to check the vehicle. This is so that the mechanic can address the actual cause of the cracked or loose belts to prevent the problem from recurring. 

Strange Smell

A strange smell coming from under the hood can be an indicator of trouble with the alternator. This problem may arise when the alternator is working extra hard and overheating. 

If you have ever been close to an electrical fire, the strange smell from a faulty alternator can be like that. The smell results from overheating in the alternator as it tries to generate more electricity. 

However, it is not just the smell of wire that should alarm you of a faulty alternator. You should also be wary if there you smell something like rubber burning. 

Because cables running from the alternator are coated with rubber, the rising temperature is likely to also burn the sheath. Another source of burning rubber smell is the rubber belt. Although the belts operate well at high temperatures, extremely hot alternators can still burn them. 

When you get the burning smell, whether it is of a wire or rubber, investigate it further because the smell might be from a different source. Take the case of overheating brakes. As brake pads work hard to slow or stop your car, they release a smell that can easily be confused with what comes from burning wires. 

Also, overflowing coolant or burning oil releases a characteristic smell that can be mistaken for an overheating alternator. 

It is important to note that smell is just a sign of the status of the alternator. So, it should not be the only basis to conclude that it is faulty. If you do not get the smell that we have described in this post, it means that the alternator is okay.

Regular Stalling or Difficulty Starting

Although different cars differ in design, issues related to ignition or to continuous operation can mean a faulty alternator. However, it will not be a good idea to conclude the two issues directly point to a damaged alternator. 

There are many other issues that can cause your car not to start. It could be because of a damaged fuel pump, frozen fuel line, or corroded spark plugs. 

When the problem is caused by an undercharged battery, this could be due to the alternator. If the alternator is not charging the battery properly, then the car will have difficulty starting. If the alternator is okay, check the state of the battery, cords, or the diode rectifier. 

Slow Accessories

Have you noted a sort of slowness in the response of different accessories? This could be the power windows or windshield wipers taking longer than usual to work. These issues can happen because of various issues, such as accessories breakdown or the motors getting damaged. 

If only one of the accessories is problematic, then you know that the problem is specific to that accessory. It’s a different case if you notice multiple accessories—from the wipers to the radio and signals—having issues. This time around, it is very likely that a bad alternator is the culprit.

Unlike when dealing with a damaged alternator belt or corroded wires, issues which you can resolve easily, slow accessories require urgent attention from your mechanic. Where possible, try to avoid using the accessories or minimize their use until they are fixed.

Strange Sounds

Aside from the other nine signs of a damaged alternator, you can also check the sound of the engine. The usual sound associated with a faulty alternator is a whining or growling noise that happens before it fails. 

For the car to run, an alternator is connected to the engine using serpentine belts or accessory belts fitted to a pulley. The design of the pulley ensures that it spins about two to three times faster on the alternator compared to the pulley on the crankshaft so that it produces power at the correct rate. If the bushings, pulley, and shaft are not aligned properly, the belt is likely to produce a whining noise. 

If you notice a whining sound, immediate checkup is called for to avoid further damage.

If the shaft is misaligned or the bearings are damaged, fix them before they can cause more damage to your car. 

Find out how much it will cost to replace an alternator

Final Thoughts

Problems with the car can be a nuisance, and it’s more frustrating if the issue is a bad alternator. That’s why it’s very important for every driver to know how the alternator works as well as how to tell if you have a bad alternator. 

As pointed out in this post, the alternator is one of the most important components in a car because it generates the electricity that runs the car’s accessories and also charges the battery. The ten signs of a bad alternator in this post only act as indicators, and you should carry further investigation to find out that it is actually faulty.