What Are the Symptoms Of a Bad Alternator?

When it feels like your car’s battery just can’t stay charged, it might be time for a new alternator.

byChris Teague|
What Are the Symptoms Of a Bad Alternator?

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Your vehicle’s electrical system is complex, but unless you drive a British car from the 1970s, it is generally designed to “just work.” Even so, things can go wrong, and one of the most common problems can leave you stranded, that being a bad alternator. 

A bad alternator can cause a dead battery and other problems with vehicle systems like the stereo and power windows. But there’s good news here, because even an automotive novice can watch a video or two and figure out how to change their own alternator. Perhaps the hardest part of it all is making sure the belt is replaced properly when the job is done.

Every one of The Drive’s crack squad of researchers can count themselves amongst the ranks of DIY mechanics that have replaced an alternator at home. Trust us, if we can do it, you can do it. Let us take you through the finer points of replacing a bad alternator.

The alternator in its natural habitat., DepositPhotos

What Is an Alternator? 

Your vehicle’s alternator is one of the three major parts needed to generate and circulate electrical power. The alternator uses magnets that spin to create an alternating current that converts energy into electricity. It’s usually found on the front of the engine and is driven by the crankshaft via a serpentine belt.

Symptoms of a Bad Alternator

Your car can communicate with you in many ways, especially if there’s something wrong. If the alternator is starting to go bad, there are a few things to look out for:

  • Warning light: The easiest way to know something’s amiss is that there will likely be a battery-shaped warning light in your vehicle’s gauge cluster.
  • Your headlights or interior lights dim or flicker, especially when using the air conditioner or stereo.
  • Other parts of the vehicle, like the power windows and door locks, start acting up.
  • You hear an unusual clicking or rattling sound.
  • Your battery continues to die, even when the vehicle is running.

Alternator Replacement Basics

Estimated Time Needed: 1-2 hours, depending on your skill level

Skill Level: Beginner

Vehicle System: Electrical

Don't go digging around until you've disconnected the battery., DepositPhotos

Safety When Replacing An Alternator

When working with your vehicle’s electrical system, there are a few things you’ll want to keep in mind.

  • It’s a good idea to wear gloves. It’s best to protect your fingers when digging around in a dark space like the underside of your vehicle’s hood.
  • Make sure you disconnect the battery. This will ensure you don’t get caught up in a spinning belt if the engine cranks unintentionally. 
  • If you’re unsure of what you’re looking at, refer to the owner’s manual. Guesswork is not a reliable methodology for automotive repairs.

Everything You’ll Need To Replace Your Alternator

You may already have what you need lying around in your garage, but be sure you have everything before getting started.

Tool List 

Parts List 

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won't need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking that is also well-ventilated. Check your local laws to make sure you’re not violating any codes when using the street because we aren’t getting you or your ride out of the clink.

Here’s How To Fix a Bad Alternator

There are kits and other methods for rebuilding a bad alternator, but we’re going to focus on a replacement instead. It’s easier and more time-efficient. It’s important to note that the steps below are a simplified version of the process. Refer to your vehicle’s service manual for specifics.

Let’s do this! 

Replacing Your Alternator

  1. Pop your hood.
  2. Disconnect the negative terminal of your vehicle’s battery.
  3. Loosen the belt tensioner that is near the alternator. This will allow slack in the belt so that both it and the alternator can be removed safely.
  4. Remove the serpentine belt.
  5. Disconnect and remove any wiring harnesses or brackets attached to the alternator
  6. Loosen connecting bolts and remove the alternator.
  7. Refit the new alternator in place of the old one and reinstall any screws removed in the process.
  8. It’s a good idea to replace the serpentine belt. Install the new one, making sure to rethread the way it came off the vehicle.
  9. Reset the belt tensioner. If it’s too loose, you’ll hear a squealing sound, but if it’s too tight it could cause damage to the belt and the alternator.
  10. Reconnect the battery cable.
  11. Close the hood and test the car.
Replacing an alternator isn't brain surgery., DepositPhotos

Get Help With Signs Of A Bad Alternator From a Mechanic On JustAnswer  

The Drive recognizes that while our How-To guides are detailed and easily followed, a rusty bolt, an engine component not in the correct position, or oil leaking everywhere can derail a project. That’s why we’ve partnered with JustAnswer, which connects you to certified mechanics around the globe, to get you through even the toughest jobs. 

So if you have a question or are stuck, click here and talk to a mechanic near you. 

How Much Does It Cost To Fix A Bad Alternator?

The costs to have an alternator professionally repaired can vary greatly, depending on the type of vehicle you drive and the under-hood configuration. In general, a replacement alternator can run between $300 and $500 for a remanufactured unit. They have been refurbished and brought back to as-new standards. On top of that cost, count on another $400 to $500 in labor. Of course, doing the job at home will save you big bucks.

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