Alternator repair is next in line once you’ve concluded that you have alternator problems.

If you want to read about the most common alternator problems and the reasons for them, click here for a separate article on that topic.

This article should, hopefully, give you some guidelines on how to deal with an alternator repair, and offer some possible solutions as well as cost estimates.

Also, at the end of this article, you have our YouTube video about the most common symptoms of a bad alternator.



There are essentially three ways to make an alternator repair (either by the mechanic or yourself):

  1. Replacing the old alternator with a brand-new one
  2. Replacing the old alternator with a used or refurbished one
  3. Refurbishing (repairing) your old alternator

More on this topic and how to make a proper choice lower in the article.


alternator voltage output

Before starting with alternator repair solutions, I will again emphasize the importance of using a multimeter when pinpointing the electrical part of the problem.

Improper voltage output is the first sign of trouble. So before making any kind of repair or expense, first, use the multimeter.

The proper voltage is from 13.5 volts minimum to 14.5 volts maximum.

If you want to know how to make an alternator voltage output check-up, click here for a separate article on that topic or watch a video on our YouTube channel.

In case of mechanical damage to the alternator (bearings, pulleys, or else) you won’t need the multimeter. These types of problems will manifest themselves literally so to say; through sound (grinding, screeching, or else), the serpentine belt may fall off, etc.

But even here you’ll need it to make a reading at the end of the repair in order to check if the alternator works correctly.

If possible, best have the multimeter at hand.


We’ll lay out the symptom and then the possible solution for an alternator repair.

The lower-mentioned solutions will mostly help if you’re repairing your old alternator.

If you’re thinking of replacing it with a new or refurbished one, take a look nevertheless as it can give a better overview of what may be wrong and help make a better decision on what course of action to take.

Namely, should you fix the old alternator or completely replace it with a new or refurbished one?

Also, it may help answer the question of whether you should make the repair yourself or let a good and trustworthy mechanic do the job for you.

So, here we go:

1. Battery warning light comes up on the dash after starting the car (fully glowing)


If the voltage is low, then check the:

  1. Voltage regulator
  2. Connections to the alternator and from the alternator to the car starter
  3. Battery terminal connections
  4. Serpentine belt (check that it hasn’t snapped)


If the voltage is too high then check the:

  1. Voltage regulator
  2. Alternator stator (if it’s burnt out)


2. Battery warning light comes up partially (barely visible but present)

In this case, the voltage is almost always too low. Check the:

  1. Voltage regulator
  2. Diode rectifier
  3. Connections to the alternator and from the alternator to the car starter
  4. Battery terminal connections
  5. Check that the serpentine belt is tensioned enough


If however the alternator voltage is too high (which is rare) then check:

  1. Voltage regulator
  2. Alternator stator (if it’s burnt out)

3. Battery warning light on the dash doesn’t come up at all


When you turn the ignition key and there’s no battery warning light at all you should check:

  1. Voltage regulator (namely the brushes on it)
  2. Connection to the alternator
  3. Commutator on the rotor (is it damaged or worn out)
  4. Rotor; namely the coil inside (this one is really rare)



4. Grinding noise from the alternator

When a grinding noise appears it is almost certain that the bearings have worn out. There are two bearings, one in the front housing and one in the rear; these bearings hold the rotor in center.



The front one is more prone to wearing out as it holds most of the load caused by the serpentine belt. Also, it is usually a ball bearing so it’s more susceptible to damage.

You should check the front one first. In a lot of cases, the rear one may not need replacement just good cleaning and some lubrication.

Nevertheless, if you have the possibility, best change both of them. Be sure to use quality brand bearings so they can last for a long time.


5. Flickering headlights


Flickering headlights mean that you have an irregular voltage output from the alternator.

This means more electricity when you rev up the engine and less when the engine idles.

In this case, check the:

  1. Voltage regulator (mostly the cause of these kinds of problems)
  2. Diode rectifier
  3. Alternator stator


It’s not unusual for this problem to be accompanied by a partial appearance of the battery warning light (weak glow when the engine is running).


6. Frequent burning of headlight bulbs


This can be a tell-tale sign of high voltage. If the multimeter shows higher voltage then 14.5 volts check the:

  1. Voltage regulator
  2. Alternator stator (if it’s burnt out)


Of course, low-quality car bulbs may cause these problems also, but even these should last at least a couple of months. If the voltage is too high, they will burn out about once a month.

If you want to learn how to change a headlight bulb, click here for a separate article on that topic or watch a video on our YouTube channel.


7. Anomalies in the electric and electronic system


These anomalies can happen both with low and high voltage.

But from what I’ve seen, most anomalies usually happen when the voltage is too high. The alternator simply overloads the system and with today’s sensitive electronic components and installations, they can go haywire (various warning lights for no apparent reason, glitches, and so on).

If the multimeter shows high voltage check the:

  1. Voltage regulator
  2. Alternator stator (if it’s burnt out)



8. Bad smell from the car battery (sulfuric smell, mostly resembles rotten boiled eggs)


The smell of rotten boiled eggs from the car battery is a sure sign of high voltage. This is a red alert and the car shouldn’t be driven for a long time in this condition. If it is, it can seriously damage the car battery and the electric installation and components.

High voltage means checking the:

  1. Voltage regulator
  2. Alternator stator (if it’s burnt out)


A word of warning: before starting any kind of repair, let the fumes out from the engine bay as they are flammable.


9. Screeching sound from the engine bay

A sharp screeching sound usually comes from the serpentine belt sliding over a stuck pulley or the belt is extremely worn out.

The main reasons for this can be:

  • The front bearing is worn out which means the rotor gets stuck and the serpentine belt slides over the pulley. You can also check the rear bearing but this is a more rare problem.
  • Faulty pulley; most modern type alternators have a clutch-type pulley. They engage the serpentine belt only once the engine is started, not while cranking. Over time, the clutch system inside wears out or breaks down completely causing the pulley to get stuck or even fall off. Once it’s stuck the belt slides over it causing the screeching sound.
  • If the serpentine belt is extremely worn out, it will slip over the pulley thus causing the screeching sound.

Solutions to these problems can be:

    1. Replace the front or both bearings on the alternator
    2. Change the alternator pulley
    3. Make sure the serpentine belt is replaced on time. Of course, if it snapped change it immediately.



10. Snapped or damaged serpentine belt


In case of an alternator repair, serpentine belts can snap or get damaged for two reasons: either it’s worn out or the alternator pulley is jammed.

The snapping can happen at a moment’s notice or a screeching sound may previously appear.

The best way to pinpoint the cause of this problem is to try turning the alternator pulley manually while the engine is turned off.

Do this especially if the serpentine belt previously snapped. If not, then take the belt off and try then turning the pulley.

If the pulley is freely turning, with no resistance, then just change the serpentine belt. In this case, it’s just probably worn out.

Take also a look at the last time you had the serpentine belt replaced.

However, if the pulley is jammed then check:

  1. Front or both alternator bearings
  2. Pulley





To broaden the topic at the beginning of this article; what are your options for an alternator repair?

Similar to car starter problems, you’ll face these solutions:

  1. Replacing the old alternator with a brand-new one


This solution holds the highest price tag, especially if the mechanic is doing the replacement (you’re not going to do anything).

Alternators are not cheap to buy for most car models but the best thing with this solution is the longevity of repair (new is new after all).

If it’s from a quality manufacturer, it should last at least 200.000 kilometers or more.

Make sure to always buy a new alternator that has a guarantee.

Do this if your alternator is severely damaged and the price of a new one is the same or lower as the repair.

  1. Replacing the old alternator with a used or refurbished one



This option offers a lower cost but less durability over time.

If you’re buying a used alternator only buy from a trusted source. Otherwise, you may end up buying another piece of junk to lay around the garage.

Regarding a refurbished one: make sure that the refurbishment was done in quality and that it perhaps has a guarantee.

Buying a refurbished one is the next best thing to a new alternator.

For this option, do it if the price is significantly lower than the cost of a new one. Just have in mind the longevity of repair as a refurbished or worse, used one, probably won’t last as long as a new alternator.

  1. Refurbishing (repairing) your old alternator

To make one thing straight: alternators are machines that are meant to be disassembled, cleaned, faulty parts replaced (bearings, voltage regulators, brushes, diode rectifier, or else), and reassembled.

A refurbished or repaired alternator (if the repair is done in quality) should last at least 100.000 kilometers without any problems.

Almost all parts can be bought separately and are meant to be replaced.

The only limiting factor for this solution is the build of the alternator itself. Some are just not “repair friendly” and demand buying a new one (it can’t be disassembled without damaging the components).

This is, unfortunately, common with modern alternators.



If you’re considering making an alternator repair I must emphasize that at least some experience around cars is desirable.

Making an alternator repair isn’t nuclear physics, but you must clearly understand what you’re doing.

Any kind of uncertainty, wandering, and carelessness can cause serious damage to the alternator, electrics, electronics, or else.

Be certain of what you’re supposed to do or don’t do it at all.

Anyway, here are your DIY options for an alternator repair:

1. Buy a new, used, or refurbished alternator and replace it yourself

This possibility is perhaps the best and most common if you have at least some experience around cars. The replacement procedure is not that complicated, the basic guidelines would be:

  • disconnect the car battery (namely the minus terminal)
  • disconnect the alternator connectors and/or wires
  • take off the serpentine belt
  • remove anchor screws and bolts (that hold the alternator in place)
  • take out the old alternator and insert the new one in place (make sure to align it with the anchors)
  • insert screws or bolts and tighten them firmly
  • mount the serpentine belt (make sure it sits in place on all of the pulleys)
  • reconnect the wiring or connector
  • return the minus battery terminal and tighten
  • turn on the car and see that everything works properly (like there is a battery warning light when you turn the ignition, that it turns off when you start the engine, there are no strange noises, etc)
  • make a reading with the multimeter and see that the voltage output is OK

Here the biggest problem could be accessibility to the alternator itself. In most cars, the alternator is located in the upper part of the engine, in a visible and easy-to-reach part of the engine bay.

If this is the case, then proceed without hesitation.

On the other hand, some car manufacturers have made this job pretty complicated and may involve serious disassembly around the alternator (various plastic coverings, additional anchors, or else).

Best make a good assessment before you start so you don’t get yourself into trouble.


2. Do the complete alternator repair yourself (together with actually fixing the alternator)

With this option, you’ll need to have some advanced alternator repair knowledge.

This option will mean taking apart the alternator, finding the malfunction, replacing parts, and successfully putting everything together.

Depending on the malfunction, you may need some specific tools like a welder, bearing removal tool, or else. Without them, some of the repairs cannot be done.

The most popular and easy repair to do, in most cases, is replacing the voltage regulator.

If you know how to take off and return the alternator, you will certainly know how to change a voltage regulator. Involves a couple of screws and maybe one connector.

As with the first option, make a proper assessment of the job ahead of you. If you judge that it’s over your head, then best don’t do it.

For the end of this part: whatever option you decide on, just be aware of your limitations and you’ll be fine.



The stated prices below highly depend on your car brand, your car parts market and the vintage of your car.

We’ll go in the same order as with the solutions for repair:

  1. Replacing the old alternator with a brand-new one

Prices for a brand-new alternator start from about 150 Euros and go up to a couple of hundred Euros, all depending on the car model and manufacturer of the part.

That’s just for the alternator. If the mechanic is going to do the whole job add another 50 Euros minimum. The harder the alternator is to take off and return, the more labor is needed thus heightening the end price.

The end sum for this option starts from about 200 Euros and can reach prices such as 500 Euros, parts plus labor.

If you’re going to make the replacement yourself, just subtract the price of labor.

  1. Replacing the old alternator with a used or refurbished one

Used alternators cost about 20 to 50 Euros depending on the car model. These alternators have been taken off used or damaged cars and no refurbishing has been done on them.

In this case, I again advise caution. If you decide on this option, buy only from a trusted source in order to avoid throwing money away.

On the other hand, if you decide to buy a refurbished one (which is much better) they go up to 100 Euros and often come with a guarantee.

The end sum for the whole job starts from 100 Euros (used alternator plus replacement) to about 150-200 Euros(refurbished alternator plus labor).

Doing the replacement yourself? Subtract the price of labor.

  1. Refurbishing (repairing) your old alternator

This option is the cheapest one if you have the needed experience for repair.

If you know what you’re supposed to do, you can make the alternator repair for a couple of dozen Euros (like in the case of replacing the voltage regulator or bearings).

More severe damages (like the diode rectifier or pulley) will cost some more, about 20 to 50 Euros for each one.

In case of a stator or rotor damage (like burning out, damaged commutator, or else) or damaged housing, you should consider a complete replacement of the alternator. Prices are such that it makes the repair highly questionable.

If you make the alternator repair by the book and with quality parts it should match the refurbished one and last for about 100.000 kilometers.

Any lack of repair quality will significantly shorten this interval.