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Five Signs It's Time to Replace Your Alternator

Wrench Wench has been in love with automotive mechanics for decades. She loves sharing advice with fellow DIY mechs and curious cats.

Alternators can be tricky beasts, but they're not very complicated

Alternators can be tricky beasts, but they're not very complicated

What Does an Alternator Do?

Alternators are really not complex mechanical components. They are a type of generator that creates an alternating current. The simplest way to explain it is that inside your alternator there is at least one spool of copper (in most cases) called the "coil" and magnets that are commonly referred to as "brushes." Those brushes rotate on an axle and brush against the copper to create an electrical charge.

The charge is then sent through various electrical components (such as the voltage regulator and rectifier bridge) and then sent out to the battery through a terminal on the back of the casing.

Another terminal brings in a small amount of electricity from the battery to keep the alternator working. It's a symbiotic relationship. The battery gives the alternator a little kick to start working and the alternator keeps a constant flow of electricity going back to the battery to keep it charged.

Five Signs You Need a New Alternator

  1. Your car has difficulty starting.
  2. Your car has dimmed accessory lights.
  3. Your car battery keeps dying.
  4. You keep smelling burnt rubber.
  5. You keep hearing a grinding or whining noise.

Below, we're going to explore five of the most common signs of a dying alternator that just about every driver notices. Because your car often will not start when the alternator is dying, an alternator that's on its way out can easily be confused with a dying battery or starter.

This list will tell you whether it's your battery or start, or if your alternator knocking on death's door. You may not see all of these symptoms, but you'll usually see at least two or three telltale signs.

If your car is having trouble starting up, it could be your alternator

If your car is having trouble starting up, it could be your alternator

1. Difficulty Starting

If your car is having trouble getting started and just turns and turns before starting up, it's possible that your alternator is wearing out. In this instance, it's likely that just a few of your brushes aren't able to reach the coil at all points where it's supposed to or that the voltage regulator is malfunctioning.

2. Dimmed Accessory Lights

If you start up your truck and notice that the dash lights, dome light, headlights, and/or radio get a little bit dimmer when your trying to start your truck, that could be an indication that your alternator isn't able to handle the load as well as it used to. Likewise, your accessories can also dim when you press on the accelerator or even dim and brighten several times, like they're slowly blinking.

3. Dead Batteries

If you find that your battery keeps dying or your car isn't able to start every time, it's worth checking out your alternator, especially if you've already had your battery tested and it passed with flying colors. This happens because the alternator is not able to recharge the battery, and it's important to catch this.

If your battery is drained and needs to be jump-started more than three or four times in a week, it could ruin the battery. Then you will have both a battery and alternator to replace, and sometimes a starter as well.

4. Burnt-Rubber Smell

This sign is common, but less common than the other signs. If, for any reason, your alternator belt is not able to freely rotate on the pulleys, it can create friction and cause the belt to heat up. When this happens, if it gets hot enough, you'll start to smell burnt rubber.

5. Grinding or Whining Noise

If you start to notice a grinding or whining noise coming from your alternator, that's another sign of an alternator problem. Grinding is usually caused by a broken, dirty, or worn-out bearing. If you're hearing a whining, it's more than likely caused by the voltage regulator telling the alternator to charge more than it should be at the time.

Alternatively, it could be that the battery is not sending enough electricity to the alternator, so if you're hearing a whining noise, it's wise to double-check the battery just in case.

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Read More from AxleAddict

Is your alternator on the verge of death?

Is your alternator on the verge of death?

Additional Signs

Here are a few additional signs of possible alternator issues:

  • Dashboard alternator warning or indicator light
  • High-pitched squealing noise (from the belt)
  • Dimmed headlights (consistently)
  • Low voltage output

There are not many other signs that your alternator is going bad that wouldn't require more detailed diagnostic tools. And in most cases, these signs are the ones that mechanics use to determine whether they should investigate the alternator as the source of your car's current troubles.

Your Alternator's Job

Your vehicle's alternator has one extremely important job: Keeping your battery charged. Additionally, your alternator also pumps in a little extra electrical power, so that each electrical system runs optimally. Without your alternator, your battery would drain in a few minutes and your car would stop. That means no starting, no running, no driving.

When your alternator is working and doing its job properly, your battery stays charged, your spark plugs have plenty of spark, and all of your vehicles accessories run without issues. When your alternator isn't working correctly, everything from your windshield wipers to your starter will experience issues.

The Parts That Go First

Over time, there are several components in the alternator that naturally wear down. In my experience, it's either the brushes (magnets) or the voltage regulator that break down the soonest.


With the brushes, it's not very complicated. Think of the copper coil as a piece of sandpaper and the brushes as a common table spoon. If you take that table spoon and rub it against the sandpaper for several hours, the spoon is going to get weaker and weaker as tiny bits of it are shaved off with every pass over the sandpaper.

Another easy analogy: over time, water gently wears down rocks. It takes a while, and happens so slowly that you wouldn't notice it until decades have passed, but slowly the water creates channels, cliffs, and caves in the rocks.

The same thing happens to your brushes. With every rotation, the magnets get smaller and smaller until they are no longer able to make a clean connection with the coil and create an electric charge.

Voltage Regulator

The voltage regulator is a bit of a different beast, and I'm not fantastic with explaining electrical components. I'll do my best though.

In your alternator, the voltage regulator's job is to control the amount of electricity produced by the alternator. Imagine this: you're walking down the street at a comfortable pace. Your brain is like the voltage regulator. It tells your body that there is no need to breathe any faster or get your heart rate up because you're not exerting yourself. Then you start walking more briskly until you're at a gentle jog. Your brain sends a signal to your heart to pump a little faster to bring more blood and oxygen to your lungs, which in turn causes you to breath a little faster. Then you start running. Your brain again sends a signal to your heart and lungs so that you bring in more air and get oxygen and blood to where it is needed.

Now here is the important part: when you start to slow down and get back to walking, your brain sends the signal to stop putting out so much energy. If your brain didn't do that, your heart would continue beating really fast, your breathing wouldn't slow down and you would quickly hyperventilate and pass out.

Your voltage regulator does pretty much the same thing. When your car first starts, if there is nothing on in your car (radio, A/C, etc...), then your alternator only needs to put out a little bit of voltage. When you turn on your radio, it puts out a little more power. When you turn on your windshield wipers, your car needs a little bit more. The more accessories you turn on, the more electricity it needs to stay running.

Nowadays, we can do a lot of things with the car. Imagine driving your car on the freeway (which needs more power) with your audio device playing music through your radio's Bluetooth function while you and your passenger's phones are charging, your heater is on because it's cold, your headlights are on because it's getting dark, your windshield wipers are going because it's raining, your headset TVs and DVD player are going in the back for the kids, and you just pushed in the cigarette lighter.

That's a lot of things to all be getting power at one time. Your alternator needs to know when each one of those things is plugged in and turned on, so that it can increase power.

More importantly, just like with your breathing, your alternator needs to know when to put out less power. As you reach a stop sign, turn off a TV, unplug your phone, turn off your headlights, etc., your alternator needs to put out less and less. If the alternator continued to put out so much power, your battery would blow up and make an incredible mess, and the acid would eat up half of your engine compartment.

Now, as I said, electricity is not my forte. I understand enough of how it works with mechanical devices and vehicles to know if it's working or not working and how to make it work again. I don't understand it enough to explain what happens when each system breaks down.

So let's just say that over time, your voltage regulator wears out and stops working like most things in life, and when its life is over, it cannot tell your alternator how to do its job correctly. When it stops working altogether, your alternator won't even turn on anymore, and, thus your car will not start.

Alternator Belt or Pulley

There are other components that can wear out as well. Your alternator is attached to a pulley system (or wheel) that has a belt on it, known as an alternator belt (go figure, right?). If the belt loosens or breaks, your alternator won't be able to send power to your battery anymore. It's rare, but I've also seen a pulley break or become bent. This usually only happens on extremely old cars where the alternator has been rebuilt instead of replaced and so the pulley is extremely old.

Wiring or Terminals

There are several elements inside and outside of your alternator that use wiring, and when the wiring gets old or corroded, it can prevent the alternator from working correctly. Likewise, there are some terminals on the back that can also become corroded and possibly break over time.

However, the more common problem with terminals is that the wiring attached becomes loose over time, which is easily fixed by tightening up the bolts or replacing them if they are stripped.


Some alternators have also work with fuses. If they do, it's common for the fuse to go out if the alternator experiences a surge of electricity that might otherwise corrupt the alternator or hurt the battery. If this happens often, it's a good idea to examine your voltage regulator.


Last, but certainly not least, if you have a vehicle that is newer than a 2001 model, you might have an alternator that is controlled digitally by a "brain" (computer). In this instance, the brain can sometimes be at fault for an incorrectly operating alternator. This is not a very common problem, but it is easy to diagnose—simply use an OBD II Code Reader.

How to Test Your Alternator

It's super easy to test your alternator with a multimeter. I'll break it down into simple steps that anyone can follow.

  1. Turn your multimeter on and set it to "voltage." If it has specific voltage settings, you want it to be able to test up to at least 20 volts.
  2. Before you turn the car on at all, look for a large red wiring attached to a terminal on the back of the alternator. Touch the red positive lead from the multimeter to the bolt on that terminal. Then touch the negative probe to anywhere on the casing of the alternator. Your multimeter should read between 11.8 and 12.8 volts.
  3. Next, keep the positive probe (+) on the alternator terminal. Now put the negative probe (-) on the negative terminal (-) of your battery. You should get the same reading as in step 3.
  4. Next, test the battery while the car is still off. Touch the positive probe (+) to the positive terminal (+) on the battery and the negative probe (-) to the negative terminal (-). The battery should also read between 11.8 and 12.8 volts. If it does, it's fine.
  5. Start your vehicle.
  6. Follow steps two and four to retest the alternator and battery with the car running. They should both read between 13.4 and 14.2 volts.

Another Way to Test

What It All Means

During step two, above, if your multimeter reads less than 11.8 volts and your battery is testing fine, then your alternator is bad.

In steps two and three, if you find that your alternator is testing in the correct range, but your battery is testing below 11.8, you have a problem somewhere between where the lead wire goes from the battery to the alternator. Check the connection at each terminal and make sure the wire isn't broken anywhere that you can reach.

During steps two and three, if you find that the voltage on your alternator drops below 11.8 and continues to drop, your alternator is creating a parasitic draw on the battery and needs to be replaced before it ruins the battery.

During steps two and three while your car is running, if your alternator tests below 13.4 and your battery tests fine, then your alternator is going bad.

During step two while your car is running, if your alternator tests above 14.2, your alternator is creating too high of a charge and likely has a voltage regulator problem.

Having the right tools for the job makes all the difference. In this case, having a multimeter can save you money and lots of time in making sure it actually is your alternator giving you problems.

Having the right tools for the job makes all the difference. In this case, having a multimeter can save you money and lots of time in making sure it actually is your alternator giving you problems.

Need a Multimeter?

Multimeters are absolutely among the number one tools I recommend that all drivers have in their toolboxes, even if they are not mechanically minded or even all that interested in the art of automotive repair.

With a multimeter, you can test your battery, alternator, starter, and more. You can also use the very same tool to test just about any electrical element in your home, RV, boat, or favorite gadgets. It's worth it to have one around.

When it comes to tools, I am definitely pro Snap-on tools whenever possible. They are definitely pricier than most other tool brands, but when it comes to tools, I've found that brand makes a difference when that brand is Snap-on.

With just about anything else, I'd say screw brand names and go for any quality item, but in this instance you want something you know you can rely on. Snap-on tools are like Jeeps or Singer sewing machines: they last.

Not only that, but Snap-on will always repair their tools and devices, even if you are not the original owner. You don't need a receipt or anything, just a tool branded "Snap-on" or "Blue Point" (a Snap-on sub-brand).

More specifically, I recommend the very common Blue Point Snap-on multimeter. It's the same kind that I own and works fantastic. On eBay, a pretty standard price for this model is $60, which is on the lower end of the price scale in terms of top quality multimeters. You can get better fancier ones, but this one is reliable and, most importantly, user-friendly.

That being said, I know what it's like to be broker than broke, so if you want to start out with a cheaper multimeter, I also have experience with a more affordable option, the common All-Sun mini multimeter from Amazon. It's only $6 and in my experience is a reasonable multimeter. It uses up batteries fairly quickly and certainly doesn't last as long as the Snap-on, but it's accurate enough to do the job.

How to Test Without a Multimeter

If going to a mechanic or getting a multimeter yourself are out of the question and you really burn with the desire to know if your alternator is a problem, here is the "shade tree" style of checking your alternator.

  1. Wear a pair of rubber gloves that protect from electricity.
  2. Start your car.
  3. Use an appropriately sized wrench to loosen your positive terminal cable (+).
  4. Remove your positive terminal cable while the car is still running and wait 30-60 seconds.
  5. Reattach the terminal cable and tighten it down.

If you find that the car dies instantly or within 30 seconds when you remove the terminal cable, then the alternator is the most likely culprit.


This method of alternator diagnostics is NOT in any way recommended, especially on cars newer than the year 2000. On vehicles made prior to 1980, there is not a high degree of risk, but the risk is still there.

What risks? Well, there is the chance that you could get electrocuted. It's not a lot of electricity, but it still hurts and can hurt your heart. There is also a very small risk from the sparks created when you reattach the terminal cable, that the battery could could overload, and that battery could blow up. I have never ever in my 15+ years of working on vehicles seen this happen, but that doesn't mean it cannot happen.

On cars made after 2000, you also run the risk of confusing the car's on-board computer or blowing fuses and relays in the computer. This is why I will always recommend that you use a multimeter or voltmeter. That being said, if you are willing to risk it and you are desperate to know (note it is rare to be that desperate), then you have this option.

DIY Repair or Take It to a Mechanic?

When it comes to replacing or fixing anything in your car or truck, you always have the option to either do it yourself or take it to your favorite local mechanic. When it comes to alternators, if you're at all mechanically inclined or you'd like to be, I would definitely recommend changing your alternator yourself.

I recommend DIY in this case, because most alternators only require a few steps from beginning to completion and even the greenest mechanic can usually have the job done within 45-60 minutes. Most of it is turning a few bolts, and the hardest part in some vehicles is getting the tension pulley down, which just takes a bit of leverage. Depending on how well you know your local shop mechanic and how nice they are, they can charge you anywhere from $75 to $200 to do the same job.

That being said, if wrenches and wires give you the heebie-jeebies, then please do take your car to a mechanic so the alternator can be changed out correctly and in a timely manner.

Purchasing New vs Rebuilding Your Alternator

If you've decided to go with the DIY option, you can go a step further than replacement and instead rebuild your alternator. This is also sometimes called "remanning" and is where you open that puppy up and replace any defective or worn out parts inside the alternator and then spit shine everything before you close it back up. Rebuilding an alternator is definitely worth the time and is very cost effective.

That being said, it's definitely a task for the mechanically inclined. You certainly don't need to be a master tech or even very experienced. You do need to have a strong understanding of basic electrical and mechanical components and assembly.

If you're not afraid of diving into new things and you don't mind not having your car immediately available to you, you can always use YouTube as an instructional tool and get the job done.

Professionally refurbished or rebuilt alternators are often just as good as brand new ones and can cost as little as half the price.

Professionally refurbished or rebuilt alternators are often just as good as brand new ones and can cost as little as half the price.

Brand New vs. Refurbished

If you've chosen option B and have decided that you'd rather not DIY, there are plenty of options available to you. The first of those many options is whether or not you want to get a brand-spanking new alternator or a refurbished one. Honestly, there isn't a great deal of difference between the two, but there is some.

A brand-new alternator is obviously unused, so you are not likely to get a dud. You'll also most likely get a lifetime warranty with your alternator, so if you keep the receipt, you can always get a free replacement one down the road.

That being said, new alternators also tend to come with that brand-new price, which is where you can definitely win with a refurbished alternator. To be honest, a refurbished alternator is really just a fancy term for one that has been rebuilt and made shiny again. It has had most of its innards exchanged for brand new components and is virtually a new alternator with an old casing.

Still, there are some things to be mindful of. Some remanufactured alternators can be duds. It's also common to find that refurbished alternators only come with a short warranty, though there are plenty out there that do have lifetime warranties. It just depends on how hard you look.

Buying Online vs. In-Store

To be honest, whenever possible, I prefer to purchase my alternators in a store, though the only reason for the preference is convenience. I'm often trying to get a part instantly, so I can take it back to my client's car and put it in.

But I have also purchased plenty of alternators from various online auto-parts stores and eBay. They work just as well, are usually more affordable, and often only take a day or two to get to you. The only big concern with purchasing them online is that if you are not sure exactly which alternator to get, you could be sent the wrong one the first time.

Most credible online stores are pretty good about getting you the right one, but like brick and mortar stores, they don't always have the proper one listed and sometimes their staff picks out the wrong one. This will mean you'll have to send it back and get the right one, but it's not a big deal if you don't mind a little wait.

They're not your better options

They're not your better options

What About Getting One From a Junkyard?

Another option is hunting down an alternator from a junkyard or wrecking yard. I'm often asked about this option from folks who literally only have or only want to spend a few bucks for an alternator. So here's the deal:

A junkyard alternator, at its best, is only going to be a band-aid. Ninety-nine percent of what you're going to get from any wrecking yard is going to be a well-used alternator that hasn't been inspected or even tested to see if it's still good. In most cases, you have to purchase it before you can test it, so you won't know how good it is until after you take it home.

You might get lucky and find one that could go a couple of months, or in rare cases even up to a year. To be honest, even if you're really in a bind, I wouldn't go for a junkyard pull. It's a big gamble, which can often cost you even more time.

That being said, if you like a gamble, you can often find places like our local Pick'n'Pull that remove highly sought-after parts like alternators and batteries. These alternators can be as cheap as $1-2 in some cases. If nothing else, you can often get a full rebuild kick for under $20 and use your new $2 casing.

Removal and Replacement

Now, because there are so many different makes and models of vehicles throughout the years, I cannot give you a customized how-to for your specific need. For the same reason, I'm not going to list the specific tools. That being said, most alternators follow these simple steps:

  1. Turn off your vehicle and disconnect the battery cables.
  2. Locate the alternator and the terminals on the back of it.
  3. Remove any terminal covers and then remove the bolts. It's wise at this point to use a bread twist tie or something similar to color mark which cable attaches to which terminal, as they are often similar is size and location. Be particularly alert to which terminal the battery wire is attached too.
  4. Locate the tension pulley. It will either be held in with a bolt, or will need to be pushed down using a breaker bar to loosen the tension.
  5. Remove the alternator belt.
  6. Remove the bolt that holds the alternator onto the armature bar that attaches it to the engine.
  7. Remove the alternator.

To replace the alternator, follow the same steps in reverse.

How to Rebuild

If you're brave and mechanically minded and you've decided you want to rebuild your own alternator, here is a great video that shows you how. In order to complete this, you'll want to purchase the correct rebuild kit for your specific alternator.

While the great contributing of mechanics of YouTube have produced plenty of videos to walk you through the process step by step, it's also a good idea to purchase a book or manual on the process. Thankfully, just such manuals are usually only a few clicks away and are very affordable. Inside you'll find plenty of easy to follow diagrams that show you how to handle and place each diode and relay just the right way.

And even in the even that something goes wrong, you can always purchase a rebuilt alternator to put in your car until you've finished dissecting and rebuilding the one in front of you.

Some Basic Tools

When it comes to changing out your old alternator for a new one, you're going to want a basic socket set with a ratcheting wrench instead of a set of crescent wrenches. Socket wrenches are much faster and easier to use, which usually results in a lot less knuckle banging and bolt stripping.

You're also going to want a decently sized breaker bar, which is essentially just a stationary socket wrench with a really long handle that can give you much greater leverage than a normally sized wrench. If your engine has a tension pulley, you're definitely going to want a breaker bar, especially if you don't have a friend handy to hold down the tension.

Last but not least, I always recommend some moderately paced music to play while you change your alternator, especially if you're newer to such tasks and still a little uncomfortable with the process.

This article is copyright (c) protected January 2016. Do not copy this article is whole or in part without including a direct link and credit back to this original article. Violators will be reported.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2016 Wrench Wench

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