8 Telltale Signs of a Bad Alternator (+ How to Confirm)

Enjoying a peaceful ride when suddenly your car’s headlights dim or the radio goes silent?

The good news? It’s not a spooky visitor.
The bad news? Your alternator might be giving up.

The alternator charges your car’s battery and powers its electrical system. If it fails, the battery will drain, causing your vehicle and its electric components to stop working.

Read on to uncover the common signs of a bad alternator, how to test it, and why driving with a faulty alternator is a bad idea.

8 Glaring Signs of a Bad Alternator

Watch out for these common signs of alternator trouble before you find yourself stranded on the road:

1. Illuminated Battery Warning Light

The battery light on your dashboard often illuminates to indicate a battery issue, but it can also signal an electrical problem with the vehicle’s charging system, including the alternator.

The warning light is triggered if the alternator operates outside its normal range of 13 to 14.5 volts. Your dashboard light may also flicker as the alternator struggles to meet the car’s electrical demands.

2. Extra Bright or Dim Lights

A dying alternator or voltage regulator supplies inconsistent power to your vehicle’s electronics, resulting in extra bright or dim lights. You may also notice flickering headlights or the lights shifting from bright to dim. If not fixed, this can cause the bulbs to burn out faster than expected.

3. Malfunctioning Car Accessories

If the alternator output is low and it isn’t supplying enough electrical power, car accessories may slow down or stop functioning.

For example, your power windows and windshield wipers might move slowly. You may also observe that the speedometer, radio, and air conditioner are acting unpredictably or have failed.

4. Whining, Screeching, or Grinding Noises

A growling or whining noise from under your car’s hood may indicate an alternator issue or problems with the drive belt.

These strange noises often occur when the belt that turns the alternator pulley is misaligned, rubbing against it, or the bearings that rotate the alternator’s rotor shaft have worn out.

5. Difficulty Starting the Car or Vehicle Stalling

If your engine has trouble starting and you only hear a clicking sound when you turn the key, it might be because a malfunctioning alternator isn’t charging your battery.

Also, if your car stalls while driving and the battery light comes on, it’s a warning sign that the alternator isn’t supplying power to the engine or powertrain control module to keep it running.

6. Dead Battery

A faulty alternator won’t charge the battery while the engine runs, leading to a faster drain. With time, the battery will lose its charge and eventually die.

If you have a dead car battery, you’ll need to replace both the alternator and the battery, as simply replacing the battery will only cause it to drain again.

7. Burning Rubber Smells

The alternator relies on the drive belt for power, converting mechanical energy into electrical energy. If the alternator seizes or has difficulty turning, it strains the belt, causing it to wear out or slip due to heat and tension.

A misaligned alternator pulley might also cause the belt to rub against other components, leading to friction and heat, which produces a burning rubber odor. Additionally, a failing alternator can overheat from excessive electrical load or internal issues, burning the insulation on wires and creating an electric burning smell.

So, if you think your alternator is experiencing an electrical issue, visit a mechanic ASAP.

8. Car Overheating

High engine temperature can be an indirect warning sign that your alternator output is low, meaning there isn’t enough power to keep the coolant circulating.

Here’s why:
A failing alternator can damage your serpentine belt, which drives other electrical components like the water pump and radiator fan. Without a functioning water pump or radiator, your engine will overheat.

But dimming headlights and electrical component failures can also stem from other car issues.
So, how can you be sure it’s an alternator problem?
Find out next.

2 Easy Methods to Test a Car Alternator

To verify if you have an alternator failure, it’s best to visit an auto repair center. The mechanic will test your alternator with the engine off and on for an accurate diagnosis.

Here are the steps they’ll take:

A. Testing with the Engine Off:

Park the car on a level surface and turn off the engine.

Locate the alternator and check for visible damage or an electrical problem. Test the car battery using a voltage meter (with the engine off, it should read around 12.5 volts).

Check the tension of the serpentine or alternator belt and tighten it if necessary to ensure the alternator provides consistent electrical power to the battery.

B. Testing with the Engine On:

Listen for a grinding or squeaking noise, which indicates an alternator bearing failure.

Recheck the voltage with the engine running, which should typically read between 13.5 and 14.5 volts.

Perform an electrical accessory stress test by turning on the radio, headlights, and AC to ensure the voltage stays stable (between 13 and 15 volts) under load. If it doesn’t, it means there’s an alternator problem.

After these tests, if your mechanic suspects an electrical issue or faulty alternator, they’ll perform an alternator repair or replacement.

Got more queries about alternator failure?
Let’s resolve them.

3 FAQs about Bad Alternators

Here are answers to commonly asked questions about a failing alternator:

1. How Do You Know If You Have a Bad Battery or Alternator?

The best way to confirm if your car has a bad battery or alternator is by jump-starting it. If the car continues running after a jump-start, the battery needs replacement. However, if it stalls again shortly after, there’s an alternator issue.

While some symptoms, like an illuminated battery warning light, are common to both a faulty battery and a failing alternator, the other signs of a bad battery are distinct.

Faulty battery symptoms include:

Slow engine cranks
Engine makes clicking sounds
Sulfur or rotten egg smell in the car
Frequent need for jump-starts
Swollen or bloated battery case

2. Can You Drive with a Bad Alternator?

No, it’s not recommended. If you have a dying alternator, your car will only run for a short time since it won’t charge the battery while the engine is running. Once the battery’s charge is depleted, your vehicle will stall and won’t restart.

Driving with a bad alternator can also cause electrical failure or damage vital components, such as the water pump, power steering pump, and fuel pump, leading to costly repairs.

3. Is It Possible to Jump-Start a Car with a Bad Alternator?

It’s possible but not advisable.

While you can jump-start a dead car battery, it’s only a short-term fix. The vehicle will run temporarily, but the battery will drain quickly without the alternator charging it.

A well-maintained and fully charged battery might only last up to 30 minutes with a malfunctioning alternator. To avoid getting stranded or damaging your vehicle’s electrical system, visit an auto repair center to replace the faulty alternator ASAP.

Restore Your Car’s Power with AutoNation Mobile Service

Identifying signs of a bad alternator, such as flickering headlights, strange noises, or a dead battery, can help avoid electrical failure and costly repairs.

If you’re experiencing alternator trouble or a dashboard warning light is on, have it checked by professional mechanics at AutoNation Mobile Service.

We’re a mobile auto repair solution offering easy online bookings. We also provide a 12-month, 12,000-mile warranty on all services, including alternator repair and electrical accessory replacement.

Contact us, and we’ll handle all your automotive needs right from your driveway.