How to Perform an Alternator Replacement (+Cost & Diagnosis)

Car struggling to start?
Before you blame the battery, consider that a faulty alternator could be at fault here.

If you’ve never heard of the word alternator, it’s ok. This rarely mentioned part converts mechanical energy into electrical energy and provides power for everything from the battery to the headlights.

Alternators rarely require replacing, but when they do, you should know the signs and, more importantly, how much an alternator replacement will cost.

We’ll address these and other burning questions on alternator replacement in detail.

This Article Contains:

How to Replace an Alternator? (A Step-By-Step Guide)
How Much Does It Cost to Replace an Alternator?
What are the Signs of a Bad Alternator?
How Do You Test an Alternator?
4 FAQs Related to Alternator Replacement

Let’s begin.

How to Replace an Alternator? (A Step-By-Step Guide)

Important: Before you begin an alternator replacement, ensure that your battery is fully charged. Don’t use the new alternator to charge a low battery, as it can affect the alternator’s internal parts.

Moreover, alternator replacement needs good vehicle knowledge, so it’s best to book an alternator replacement service instead of a DIY attempt. Also, this auto service isn’t as simple as a tire rotation; you’ll need a couple of special tools for the job.

Tools Needed:

Voltmeter
Belt tensioner
Replacement serpentine belt
Basic hand tools
Rags and gloves

Here’s how a mechanic will replace a failing alternator:

1. Disconnect the Battery

Before performing any alternator work, the auto mechanic will turn off the ignition and disconnect the negative terminal of your car battery. This is to prevent any circulation of electrical energy through the vehicle’s electrical components.

2. Locate the Alternator

An alternator can be identified by its aluminum body, vents, and an operative cooling fan. It’s usually bolted to the front or side of the vehicle’s engine. Some cars may require the mechanic to access the alternator from underneath the vehicle. In that case, they would also need a hydraulic jack, jack stands, wheel chocks, etc.

While replacing a vehicle’s alternator, the auto mechanic will also inspect every essential component of the charging system. These include:

Drive belt (serpentine belt): They’ll look out for cracks, frays, and other wear signs on the drive belt and replace it if needed.

Drive belt tensioner: The belt tensioner must not be excessively tight or loose. They’ll also check the alignment of the drive belt and alternator pulley(s).

Electrical connections: They’ll ensure that all alternator pigtail connectors, wires, and harnesses are clean and intact for an adequate flow of electrical energy to every electrical component.

Additionally, they’ll look for any oil, grease, or antifreeze contamination on the alternator’s aluminum body.

Car care tips: Regularly wipe down your engine and the alternator case with a light solvent to keep them clean and free from dirt, dust, or debris.

4. Remove the Bad Alternator

Once they’ve inspected and replaced every essential electrical component, the mechanic will disconnect and unbolt the alternator from the vehicle’s engine and mounting brackets.

5. Install the New Alternator

It’s essential to match the new alternator with the faulty one to ensure that the size and the connectors align. Once confirmed, they’ll install the new alternator and its electrical connections.

Wondering how much an alternator replacement would set you back?
Keep reading!

How Much Does It Cost to Replace an Alternator?

Parts and labor costs for an alternator replacement service depend entirely on what type of vehicle you drive. The alternator replacement can cost anywhere from $150 up to $1000. If the serpentine belt also needs a replacement, expect to pay an additional $20 – $50.

Also, some alternators are easier to replace than others, according to their location in the engine bay. Generally, the lower it sits, the more engine components need to be removed to access it. That said, most ASE certified technicians will complete this auto service in an hour or two, including the initial testing and diagnosis.

But how do you know if you have a faulty alternator?

What Are the Signs of a Bad Alternator?

Here are some tell-tale symptoms of a bad alternator:

Car won’t start: Often, the first sign we get that something is wrong with the alternator is a vehicle that refuses to start because of a flat battery. Starting an engine puts a significant load on the battery, and it takes time to recharge. If the vehicle’s alternator isn’t providing enough voltage to recharge the battery, it will quickly go flat.

Sluggish accessories: Your vehicle’s electrical components — like power windows — will move more slowly than they typically do.

Dim or flickering lights: An insufficient electrical charge from the bad alternator will cause the interior lights and headlights to flicker or glow dimly.

Active battery light: Sometimes, the battery light on your dashboard may also activate due to a bad alternator instead of a failing battery. This happens when the alternator is unable to charge the battery.

Next, we’ll cover the process to confirm that you indeed have a bad alternator.

How Do You Test An Alternator?

Your auto repair mechanic will use a multimeter to determine if your car alternator needs a replacement.

Here are the alternator testing steps they’ll follow:

Turn off the vehicle and wait for a few minutes to get an accurate reading.

Ensure that the battery terminals are clean.

Switch the multimeter to the 20 DC volts (DCV) setting.

Attach the multimeter’s black probe to the negative battery terminal and the red probe to the positive terminal. The resting voltage for your vehicle battery should be around 12.6V. A lower reading than this can indicate something is draining the battery.

They’ll do the same test on the battery but with the engine running. The output for the car alternator now should be between 13.8V and 14.4V. Any reading over or under this range indicates the alternator is overcharging or undercharging the battery.

They’ll verify the other signs to confirm the alternator issue.

If you still have doubts about your alternator replacement, the following section will tackle some queries.

4 FAQs Related to Alternator Replacement

Here are answers to commonly asked questions about the alternator:

1. How Does an Alternator Work?

The alternator is a small generator that converts mechanical energy into electrical energy. It uses a drive belt and a couple of pulleys that help generate alternating current output from the alternator’s stator. A rectifier converts this alternating current output into a direct current, which activates your car’s electrical system.

By doing so, the alternator, along with the voltage regulator, helps power accessories like headlights, electric power steering, power windows, instrument cluster, radio, etc. The alternator also charges the battery while you drive.

2. Can You Fix a Bad Alternator?

While they can last fairly long, when an alternator issue occurs, it’s best to replace them rather than go for an alternator repair. Repairing or rebuilding the internal parts of a bad alternator can cost almost as much as an alternator replacement service. More so because a new alternator will last longer than a refurbished one, and it usually comes with a warranty.

However, in some circumstances, opting for an alternator repair may make sense. This includes replacing a worn drive belt, bearings, voltage regulator, diodes, loose or frayed wiring, etc.

Car care tips: Ask your mechanic to check your drive belt during annual car maintenance. This can help prevent the alternator from overworking and wearing out faster.

3. Can a Car Run with a Bad Alternator?

While a car can technically run with a bad alternator, you should avoid driving.

A failing alternator won’t be able to recharge the battery sufficiently, so if you are driving and the engine cuts out or stalls, the battery likely won’t provide enough electricity to power the starter and crank the engine, leaving you stranded. This is particularly dangerous if it occurs at an intersection or on a busy road.

So it’s best to book an auto service if you start noticing the signs along with an active dashboard warning light.

4. How to Tell if it’s a Bad Battery or a Bad Alternator?

Here’s a surefire way to test if you have a bad alternator or battery:

Connect a running battery to your car’s battery using jumper cables.
Let it charge for a couple of minutes, then try starting your vehicle.
Once it starts, remove the jumper cables. If your engine stalls, your alternator has probably gone bad.
If it continues to run, your battery needs a replacement.

Wrapping Up

Testing and replacing an alternator isn’t difficult, but it requires some technical know-how. You should also watch for the tell-tale signs of a bad alternator to avoid being stranded on the road.

If you’re unsure — an easy solution is to get your alternator inspected and replaced by an expert at AutoNation Mobile Service.

We’re a mobile auto repair service available seven days a week. Even if you need us at 0800 am in the morning, our mechanic will be at your driveway. We also offer a 12,000-mile, 12-month warranty on every repair.