Car Alternator Problems? 8 Most-Common Problems & Solutions

Your car’s alternator generates power to keep your car running and recharge your battery. There are many reasons why the alternator fails to do its job which can lead to bigger problems to deal with.

We’ll cover the most common issues related to the alternator and how to fix them.

#1 – Your Battery Light Comes On Signaling An Electrical Problem

Without the engine running, and the alternator generating power, the voltage in your car should be approximately 12 volts. When the engine starts, the alternator should produce power and the voltage should rise to 13.5 – 14.5 volts.

If the alternator fails to generate the additional voltage, the car will illuminate the battery light in the gauges or display a message related to an electrical issue. The battery light is typically red, showing that you have a major problem that needs rectification as soon as possible.

How to Fix It

Alternators can last up to 150,000 miles or more, which may span years or decades of car ownership. They will eventually fail as the electrical components and bearings inside the housing corrode and wear out.

Most alternators can be rebuilt with new internal parts if the parts are available. More often the best and most economical solution is to buy a replacement alternator and install it in your car.

Car alternator explained

The removal procedure should take basic tools to remove the belt that turns the alternator pulley and remove the fasteners holding the alternator on the engine. From there the new alternator can be installed, the belt returned to the engine, and the electrical connection made to the alternator.

#2 – Your Headlights Flicker or Dim With The Engine Speed

Your headlights draw the most power of any light in your car’s electrical system because they use a high-powered incandescent bulb.

When the alternator doesn’t produce sufficient power for the electrical system, the headlights may flicker or dim while the car is idling.

As you drive faster, and the engine revs higher, more power is generated. This additional power will make the headlights shine brighter. With the up-and-down revving of the engine, the headlights will shine brighter and dim in the same manner.

This dimming is a sign that your alternator isn’t producing the correct amount of power for your car. That could be because the alternator is slowly failing, or the system requires more power than the alternator can produce.

Read Also: 8 Popular Cars With Strong Headlights

How to Fix It

A failing alternator can slowly produce less and less power until it finally stops producing power. If you notice your headlights are dim when you start your car, it may be a sign that your alternator is about to fail. Once you recognize the sign, the alternator should be replaced before it stops working altogether.

You can test the output of the alternator with a multimeter connected to the battery.

A fully charged battery should have approximately 12 volts without the engine running and the ignition turned off. When you turn the key and start the engine, the alternator should begin to produce power. The voltage at the battery should increase to 13.5 – 14.5 volts. If that doesn’t happen, the alternator should be removed and tested to prove it is good or bad.

Your local auto parts store has a machine that can test the alternator and ensure that it is faulty. With that knowledge, the alternator can be rebuilt or replaced by a new unit.

If the alternator is tested and shows to be good, it may not produce enough power for your car. That typically happens when new electronics are added to a car that didn’t originally have them.

Adding a new radio, large amplifier, or extra lights may create a situation where your alternator will consistently struggle to generate enough power for the electrical system. You may need to upgrade your alternator to a unit that can produce more power.

One other potential problem could be that the battery cables are corroded or other wires are damaged. This can prevent power from being transmitted through the car. The corrosion can be removed and the wires can be fixed, which will allow the power to be distributed again.

#3 – You Frequently Need To Replace Your Headlight Bulbs

Headlight bulbs are a great indicator of your alternator’s health. If the bulbs dim at low engine speed, it can indicate the alternator is going bad.

On the opposite side, if the headlight bulbs are frequently burning out, it can be an indication that your alternator is producing too much power. It may be overloading the headlight bulbs until they fail or burn out the filaments inside.

How to Fix It

Your alternator should produce more power than our car requires if it is sized correctly. The car has a voltage regulator that keeps that extra power from damaging electronics in the vehicle.

Older cars may have an external voltage regulator outside of the alternator, but newer cars will have the regulator inside the alternator housing. A faulty regulator will allow that extra power to be distributed through the car, and the bulbs that typically burn out the most from overpowering are the headlight bulbs.

If the regulator is faulty, it should be replaced. An external regulator is easy to unplug from the car and remove. A new unit can be installed in its place to keep excess power from overloading the car’s electrical system.

A regulator internal to the alternator may be available for purchase, and the alternator can be opened to replace the internal regulator.

If a complete kit is available, you should rebuild the complete alternator with new electrical components and bearings to prevent any future problems from old components. If a rebuild kit isn’t available, or it is more economical to replace the complete unit, buy a new one and just replace the whole alternator.

#4 – Your Lights Pulse Like A Heartbeat

Your alternator should produce a consistent voltage between 13.5 – 14.5 volts when the engine is running. That voltage will vary slightly with engine speed, but your lights should not pulse like a heartbeat.

If the pulsing lights make you feel like a night at the disco, your regulator may be failing to keep a consistent voltage for your electrical system.

How to Fix It

You can test the voltage at your car battery with a simple multimeter. S

et the meter on DC (direct current) voltage and test the amount of voltage at the battery connection. It should be stable between 13.5 and 14.5 volts with the engine running.

If it is varying wildly, the alternator or regulator is failing and should be replaced. Buy a rebuild kit for the alternator to replace the failing parts or just replace the complete alternator with a new one.

#5 – Your Car Battery Smells Like Rotten Eggs

Your car battery shouldn’t have a distinct smell. If the area around the battery smells like rotten eggs, that is a sulfuric smell coming from your battery.

The alternator is overcharging the battery and causing the liquid inside the lead-acid battery to boil.

How to Fix It

An overcharged battery will boil the lead-acid liquid inside the battery until it is gone. The boiling process creates a sulfuric smell that smells like rotten eggs.

The overcharging is caused by the voltage regulator not controlling the voltage being sent to the battery. The regulator should be replaced if it is an externally mounted unit.

If the regulator is internal to the alternator, it may be cheaper to replace the complete alternator than to have just the regulator replaced inside the alternator.

Read Also: Car Battery Problems? 12 Most-Common Issues and Fixes

#6 – The Alternator Is Making A Grinding Sound

The alternator has bearings that support the shaft inside the housing. These bearings can corrode or wear out and cause a grinding sound when the engine is running.

How to Fix It

The bearings may be available separately from the other alternator components, and they can be replaced. If they aren’t available separately, the whole alternator can be replaced with a new unit.

#7 – The Alternator Belt Is Making Noise Or Is Broken

The main belt that turns the alternator pulley shouldn’t make a significant amount of noise, and of course, it shouldn’t break.

If the belt is squealing, it may not be tight enough to keep consistent contact with the pulley. That may lead to inconsistent charging from the alternator too. A belt that is too tight may not make noise, but it can prematurely wear out to the point of early failure.

How to Fix It

The alternator belt should have slight up-and-down movement at the proper tension. Most newer cars with one major serpentine belt have an automatic tensioner for the belt.

If the tensioner is bad, it can cause the belt to be too loose and the alternator won’t charge the battery properly. If the belt is cracked or broken, it should be replaced with a new one.

#8 – The Battery Cables Or Jumper Cables Were Installed Backwards

The battery has markings to indicate which terminals are positive and negative, but the cables can be switched or installed backward. Red indicates positive and black indicates negative.

In poor lighting, they can look like a similar color. When that happens, significant damage can occur to the rectifier, diodes, and regulator in the alternator.

How to Fix It

Damage may not occur if you touch the wrong cables to the battery terminals, but if they cause a power surge it can damage the alternator and electrical system.

You will need to rebuild or replace the burned components in the alternator, or completely replace it. Also, check the fuses in the car to ensure the incident doesn’t cause damage elsewhere in the electrical system.


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