7 Common Signs of a Bad Alternator You Shouldn’t Ignore

A failing alternator could catch you off guard and leave you stranded at the most inconvenient of times. So, you’d want to identify a bad alternator early, saving you time and money.

But what are the signs of a bad alternator?
Can you still drive if your alternator is faulty?

In this article, we’ll answer these and other frequently asked questions to give you a better understanding of your cars alternator.

Let’s get started.

7 Bad Alternator Symptoms

There are several indications of a failing alternator.
Here are some of the most common:

1. Alternator or Battery Warning Light Turns On

An illuminated dashboard warning light is likely the most common sign of an electrical issue with your car.

Most cars built within the last decade include a dedicated alternator warning light (“ALT” or “GEN”) to signal alternator trouble. Some cars may use the battery light or Check Engine Light instead.

However, if your alternator has recently started having issues, the warning light may flicker instead of being continuously lit.

2. Dim or Flickering Lights

Because the alternator powers your cars electrical system, one of the first signs of a bad alternator is an electrical failure.

Dim or flickering headlights are a key visual indicator of an alternator problem. They may occur due to an inconsistent voltage supply from a failing alternator.

You may also notice the cabin, console, or tail lights getting dimmer.

What’s more?
The opposite may also happen when the alternator supplies higher-than-required voltage, resulting in unusually bright lights.

3. Underperforming Electrical Systems

You might notice your car’s power windows rolling slower, the speedometer acting up, or the stereo system’s output getting softer due to alternator trouble.

These are tell-tale signs of an issue with your vehicles electrical system.

Which of your car’s electrical accessories start acting up usually depends on several factors, such as how well your alternator is still performing and how your car is programmed.

Many modern vehicles have a preprogrammed set of priorities for routing electrical energy. Safety is usually the primary factor, so when experiencing an electrical problem, the stereo and air conditioning will likely go out before the headlights.

4. Strange Noises

Cars make tons of noises, some are completely normal, while others indicate serious problems.

One sound common to a bad alternator is a growling or whining noise.

This sound is generally because of a misaligned alternator pulley and drive belt or a worn-out alternator bearing.

It gets worse:
Ignoring alternator failure can lead to faulty engine bearings, which may cause a rattling sound and trigger the engine oil light.

5. Unpleasant Smells

If you start noticing a strange smell, it could be that your alternator is working too hard or overheating, causing problems with the cars electrical system.

Why?
Because the alternator’s belt is near the engine and under constant tension, it may wear out over time, producing an unpleasant burnt rubber smell.

If it smells like an electrical fire, this could be the alternator’s wires, and you could face alternator failure soon.

6. Bad Belts

Unlike an electrical problem, bad belts are a little less common.

However, a worn or cracked alternator belt or one that’s too tight or loose could lead to an alternator issue.

It’s easy to visually inspect an alternator belt by opening the car’s hood and checking for cracks or signs of excessive wear. But bear in mind that the belt must have the correct amount of tension; too much or too little could cause an alternator malfunction.

As a result, it may be best to avoid causing any additional damage and let a mechanic diagnose the problem.

7. Regular Stalling or Difficulty Starting

A malfunctioning alternator may not charge the car battery properly, resulting in a dead battery and trouble starting the engine.

If your car is stalling after turning it on, the spark plug system may receive inadequate electrical power from the alternator.

Aside from an alternator problem, many other issues can also cause frequent stalling and difficulty in starting your car. Things like a bad battery or a faulty fuel pump can result in similar symptoms, so be sure to check everything else going on with your vehicle to find the root of the problem.

Now, let’s go over some FAQs about your vehicle’s alternator.

8 Alternator FAQs

Here are answers to common questions you may have about alternators:

1. What Is an Alternator?

A car’s charging system has three auto part components: the car battery, the voltage regulator, and the alternator.

The alternator is the auto part responsible for powering the electrical components of your vehicle and charging the battery as the engine runs. It’s located near the engine’s front end and converts mechanical energy into electrical energy.

The alternator comprises parts like the:

Rotor: It’s connected to the crankshaft through an alternator pulley and drive belt system. The rotor spins with the help of an alternator bearing fixed on the shaft.

Stator: The rotor spins inside the stator, which has wire coils and produces an electric current due to electromagnetic induction.

Rectifier: It consists of diodes and converts the AC alternator output to DC voltage used by the car’s electrical system.

Diode trio: As the name suggests, it consists of 3 diodes and converts the stator’s AC output to DC. This DC voltage, in turn, is applied to the rotor through the slip rings.

Brushes and slip rings: They are located at each end of the rotor shaft and help apply a DC voltage to the rotor. This applied voltage is what makes the rotor act as an electromagnet.

In addition to these components, some alternators have a built-in voltage regulator that ensures your car battery and other systems get a controlled voltage supply.

The alternator output is used by every electrical component, including the spark plug system, air conditioning system, headlights, and power windows.

2. How Long Do Alternators Last?

While the alternator should ideally last as long as your vehicle, that’s not always the case. It’s hard to say exactly how long an alternator will last since many factors affect its longevity.

Some cars may experience an alternator failure after 40,000 miles, whereas others will go 100,000 miles without running into issues.

Remember, the alternator only had to power a few things in older cars, like the interior and exterior lights, the radio, and one or two other electrical components. So, vehicles with many electrical accessories may increase the load on an alternator, affecting its lifespan.

3. How Do I Know if I Have a Faulty Alternator or Battery?

In its simplest form, starting and running an engine involves three steps: the battery first delivers a jolt of energy to the starter motor, powering up the car. In turn, the engine powers the vehicle’s alternator, which recharges the battery.

If you’re unsure whether you just have a bad battery or your car alternator needs replacing, jump-start your car:

If the engine starts but then dies immediately after, you could be dealing with electrical failure, indicating the alternator probably isn’t charging the battery.

If your car starts and stays running, but you can’t start it again using its own power, you will likely have a bad battery.

You can check the alternator with the help of a voltmeter or multimeter.

4. How Do I Check the Alternator Using a Multimeter?

A multimeter can measure the potential difference in electricity between two points on a circuit. If you suspect a bad alternator, you can use a multimeter to check if it’s functional.

Here’s what a mechanic would do:

Park the car on level ground and engage the parking brake.
Set the multimeter to a value of 20V DC.
Connect the multimeter to the battery terminals (red to the positive and black to the negative terminal).
Check the battery voltage — it should be close to 12.6V. A lower value indicates a car battery problem.
Turn on the engine and recheck the multimeter’s reading. This time it should be at least 14.2V.
Turn on each electrical component of the car, including the headlights and cabin lights, windshield wipers, and stereo system.
Recheck the cars battery voltage — it should read a value above 13V. A lower reading implies an alternator problem.

5. Can I Drive My Car With a Bad Alternator?

Yes, but it depends on the seriousness of the issue.

If the alternator is functioning with reduced efficiency, you can still drive your car; however, it’s best to avoid doing so.

If you have a car with electrical power steering, it can pose a safety hazard as you could lose all steering power.

Also, if the alternator fails due to a snapped serpentine belt, the water pump won’t work. This affects the cooling system and can damage the engine by overheating. It’s best to avoid such a risk as the average cost of a complete engine repair (rebuild) is around $2,500 – $4,500.

If your alternator stops working entirely, you have limited time before your car stalls without restarting due to a bad car battery. If you’re driving, and a dashboard light signaling a dying alternator turns on, shut off all the electrical accessories and find a safe place to park.

6. What Causes an Alternator to Go Bad?

Your car’s alternator may fail for various reasons:

Age and use-related wear is often the reason behind a dying alternator.
Engine oil or power steering fluid leaking onto the car alternator can lead to its failure.
Prolonged idling while using multiple electrical accessories can prematurely wear the alternator.
Salt and water intrusion can result in a malfunctioning alternator, especially if it’s located near the engine’s bottom.

7. What Causes a Car’s Battery to Go Bad?

You’re more likely to face a weak battery than a failing alternator. The following reasons can contribute to a battery problem, resulting in a lit battery light:

Idling for long leads to sulfation, preventing the battery from charging completely.
Extremely cold conditions can result in a weak battery by slowing down chemical reactions and reducing the power delivered by it.
Battery corrosion on terminals hampers charging.
A faulty alternator can lead to a weak or dead battery due to inadequate charging.

8. How Much Does an Alternator Replacement Cost?

An alternator replacement can be expensive, depending on your vehicle’s year, make, and model. They may range roughly from $500 to $2600.

However, you can seek alternator repair as a cheaper alternative to buying a new one.
Alternator repair can cost about $70 – $120 for removal and installation plus an additional $80 – $120 rebuilder’s charge.

Final Thoughts

While your cars alternator should last the lifetime of your car, it could also fail prematurely under certain circumstances.

Whenever you notice problems with your vehicles electrical system, don’t ignore them, as they can indicate a potential alternator issue and a bad car battery. Plus, a dashboard light may not always pop on to warn you.

For easily accessible help, contact a reliable auto repair service like AutoNation Mobile Service.
We’re available seven days a week, and all repairs and maintenance are covered by a 12-month, 12,000-mile warranty — for your peace of mind.

Once you’ve made a booking, our expert mechanics will come to your driveway, ready to fix your alternator problems in no time!