Alternator problems are considered one of the more serious car problems.

Main reason is that, once they appear, the car can be left without electric power rendering it practically useless.

The alternator will seldom let you down at a moment’s notice. It’s usually a gradual process so noticing symptoms on time can mean the difference between a safe drive and being left stranded.

This article will hopefully help you spot these problems on time and avoid further damage and unneeded cost.

At the end of the article you can also read about the common reasons of alternator problems as well as how to possibly avoid them.

If you want to see how to solve alternator problems, click here for a separate article on that topic.



Alternator is a generator of alternate current which is driven by the power of the engine via the serpentine belt.

But how does a generator of alternate current (AC) supply a car with electricity when the car has a direct current (DC) installation?

Well, a set of diodes inside the alternator (aka the diode rectifier or diode bridge) turns alternate in to direct current enabling the alternator to effectively be a generator of direct current.

A piece of engineering marvel, in my opinion as it combines the sturdy and reliable design of an AC generator and makes it in integral part of a DC installation.

The alternator revolutionized electric supply in cars rendering the old unreliable DC generators (better known as dynamo machines) obsolete.

This is a definition in a nutshell. If you’re interested in a more detailed definition, click here for a great explanation on Wikipedia.

What’s even more important, you can see there all the parts of the alternator so you can get a better idea of what may cause alternator problems.




Once you’ve seen tell-tale signs that you have alternator problems (flickering lights, battery warning light comes on or else), the best way to start trouble-shooting this problem is to check the alternator voltage output.

This is done with a multimeter.

You don’t have to use a multimeter if you have alternator problems of a mechanical kind (pulleys, bearings or else).

These kind of problems will manifest themselves in other obvious ways (grinding or screeching noise, snapping of the serpentine belt or else).

Nevertheless, it will come handy even in this situation since you’ll have to check the voltage output once the repair is done.

By checking the alternator voltage output, you’ll know for sure if the alternator is “guilty”.

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

If you want to learn how to make an alternator voltage check on your car, click here for a separate article on that topic or watch a video tutorial on our You Tube channel.



(Once more, if you want to see how to solve the lower mentioned alternator problems, click here for a separate article.)

The most common alternator problems would be:

1. Battery warning light stays on after starting the car


Once you start the car, the battery light doesn’t turn off. Instead it stays on all the time, fully glowing.

2. Dim battery warning light (barely visible but present after starting the car)

When the car is started, the battery warning light almost goes off but continues to glow in a dim fashion. It can be barely visible or almost fully lighting up.

In some cases it may turn off if you rev up the engine. Otherwise it will stay this way the whole time.

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


When you turn the ignition key, before starting the car, the warning light doesn’t light up at all.

There will be also no warning light when the car is started.

4. Grinding noise from the alternator


The noise sounds like something broke up really bad in the engine bay. Grinding, clanking, shredding are all noises that can come from an alternator problem.

5. Flickering head lights


When you turn on the headlights and they pulse when you rev the engine, (headlights don’t have a steady, constant quality beam) you probably have an alternator problem.

A small pulsing is OK and is more or less present in many cars, but a strong fluctuation is bad.

One of the first and most obvious tell-tale signs of an alternator problem.

6. Frequent burning out of headlight bulbs


Accompanied by flickering headlights is a constant and abnormal burning out of headlight bulbs.

If you have to change the light bulbs in short intervals (like once a month), grab a multimeter and check the alternator voltage output (if it’s too high).

Changing the headlights bulbs is usually an easy job. If you want to learn how to do it, click here for a separate article on that topic or watch a video tutorial on our You Tube channel.

7. Anomalies in the electric and electronic systems


Electric and electronic installations and components are highly dependent on a steady and proper input of electricity.

Alternator problems can cause strong fluctuations of the power supply to these components.

This will manifest in things like check engine light coming up for no reason, instruments on the dash going haywire, glitches in the electronics and so on.

Maybe the worst part of this problem is that many drivers replace expensive electronic components for nothing when the whole problem was actually caused by the alternator.

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


If a sulfuric-like smell, resembling rotten boiled eggs, is coming from the engine bay, it’s a sure sign of alternator problems.

This faulty smell is caused by the car battery (namely the electrolyte) if the alternator is producing too high voltage.

The battery acid starts to “boil” inside the battery causing these bad-smelling vapors.

This problem is pretty dangerous as these fumes are flammable.

Also,if the car is driven in this state for a prolonged period of time, it may cause permanent damage to the car battery.

9. Screeching sound from the engine bay

alternator-problems-screeching noise

Unlike the grinding noise, this is a high-pitched sound. Mostly comes from either a stuck alternator pulley or a severely worn out serpentine belt.

In both cases, the screeching sound is caused by the excessive friction between the pulley and the serpentine belt.

10. Snapping of the serpentine belt


Common cause as the serpentine belt is under constant tension. Not replacing it on time, stuck alternator pulley or a faulty bearing are common causes of this problem.

Worst thing about this problems is that it can snap at a moments notice.


Main causes of alternator problems (at least from what I’ve seen) are:

  • Lack of maintenance



This is the first and most common reason of them all.

Alternators have a service interval of their own. Many drivers neglect this fact which can lead to having alternator problems.

The service interval is pretty lengthy (about every 200.000 kilometers) which is perhaps why many people forget about this.

Maintenance consists of the alternator being disassembled, cleaned, faulty or worn out parts replaced and reassembled.

Other option is a complete replacement with a new or refurbished alternator.

Not paying attention to this interval can mean total failure of the alternator both mechanically (bearings, pulley, etc) or electrically (lack or over-producing of electric power).

  • Installing low quality spare parts

If maintenance is done with low quality parts you’ll have trouble again very soon.

Here you should always use quality parts if you want the repair to last for a long time.

It will pay off as a quality made alternator service will guarantee at least 100.000 kilometers (even more) without an alternator problem.

  • Mixing up battery poles when connecting a car battery



This is a very common mistake, especially among drivers who want to make a car battery replacement on their own but don’t have experience.

Although markings on the battery terminals and clamps are clear, people do switch them up. This causes, in a lot of cases, damage to the diode rectifier inside the alternator.

Besides this, it can cause damage to the electronic car components.

If you want to learn how to properly connect a car battery, click here for a separate article on that topic.

  • Improperly jump starting a car


As with the car battery, switching jump cables can cause alternator problems.

Namely, if you switch the plus and minus cables (from the “donor” car to yours) you can again damage the diode rectifier.

Even worse, you can damage the “donor” car as well.

Here also, additional damage can be caused to other electric or electronic components.

We have a separate article on how to properly jump-start a car; you can read it by clicking here.

  • Power surges in the electric installation


Any kind of sever short-circuit or electric overload may also cause an alternator problem. Diode rectifier and voltage regulators are especially vulnerable to this.

  • Over-tension of the serpentine belt


This was a more often problem in previous, older cars when the tension was done manually.

Nowadays, on most cars the belt tensioner has a spring of its own so as the serpentine belt loosens over time, the tensioner keeps it in place and tightened firmly.

Nevertheless, if the tensioner wears out, it can cause alternator problems (loose belt or worse, the belt can totally fall of the alternator pulley).

  • Broken or damaged wires


This happens mostly in older cars duo to material fatigue of the electric installation.

The most common places to check are the connections on the alternator as well as the connection on the battery terminal, namely the plus (+) connection.

Another place worth checking is the connection from the alternator to the car starter.

On most cars the main plus (+) power cable goes from the alternator to the starter and then to the car battery.

A common cause is also physical damage to the wiring.

When some recent mechanical work has been done around the alternator vicinity (like belts, other pulleys, water pumps or else) and accidental damage to the wiring can happen.

  • Filthy or rusty contacts or connectors



As with all other electric appliances on the car, rust, filth and bad contacts are arch enemies of proper functioning.

Check that all the connections to the alternator are free of rust and filth.

If there are any signs of these, clean them as soon as possible as a weak contact can mimic a more serious alternator problem (stator, diode rectifier or else).

The alternator cables are usually held in place with a big plastic connector or separately by nuts or screws.


For the end of this article I would like to share a few tips for avoiding alternator problems in the first place:

  • Proper maintenance


Be aware of the alternator service interval and don’t wait for the bitter end. Your mechanic or garage should warn you about this. You can also take a look at the service book on the last alternator check up.

My advice is to pay attention about every 200.000 kilometers.

Know this also: you don’t have to wait this long. You can have the alternator cleaned and maintained before this interval, prevent a malfunction and significantly prolong the service life of your alternator.

  • Make an alternator voltage check up part of your regular car check ups


Just like with other car checkups, make a habit of checking the alternator voltage from time to time; once a month should be enough.

Multimeters are not that expensive to buy. A couple of dozen Euros will buy you a very decent one.

Well spent money in my opinion as it will help spot alternator problems on time and maybe save you some money and trouble.

  • React to alternator problems immediately

When the first tell-tale signs of alternator problems appear, react as soon as possible.

Prolonging may not only cause severe damage to the alternator, but can also damage the electric installation, electronic components, car battery or else.

My main point: a simple alternator problem that has a small price and is easy to fix can turn in to a big and costly problem if you wait.

As mentioned in the beginning of this article: alternators are gems of automotive technology with a very sturdy design.

Just a little care and attention will ensure that you have proper electric supply on your car for many thousands of kilometers.