How To Replace the Alternator in Your Car

If your car or truck won’t hold a charge, or if you’re having signs electrical gremlins like dimming headlights, you probably need a new alternator.

“If you keep a vehicle over 100,000 miles, chances are good that you’ll encounter a bad alternator,” says Melanie Musson, an auto industry expert with AutoInsurance.org. “You may think you have a bad battery, but if your battery is within its lifespan, the next thing you should check is the alternator.”

Luckily on many cars changing an alternator is a relatively easy DIY process and can be accomplished in under an hour. It’s also a good way to save a lot of money on repair shop labor costs.

Here’s how to figure out if your vehicle’s alternator has gone bad, plus all of the steps you’ll need to learn for how to replace it.

What does an alternator do?

Think of your car’s alternator as a small but mighty electric generator. It charges the car battery and runs a vehicle’s electrical system while the engine is running. It’s one of three essential components of a vehicle’s electrical system, along with the battery and voltage regulator.

How does an alternator work?

Located near the front of the engine, your car’s serpentine belt wraps around a pulley attached to the alternator. As the engine runs, the alternator takes the mechanical energy generated by the serpentine belt and turns it into electrical energy.

The pulley turns a rotor shaft inside the alternator that spins magnets. This create an alternating current, which is then turned into direct current by diodes within. That direct current powers the electrical systems in your car when it’s running.

Signs of a bad alternator

If the charging light is lit on your dashboard or your battery won’t stay charged, chances are you’ve got a bum alternator. (For some cars, the check engine light might pop on if the alternator is failing.) Other signs of a bad alternator include dim or flickering headlights.

“Worst case scenario, a faulty alternator can cause your battery to drain completely, which means your car won’t start,” says Duane “Doc” Watson, a technical trainer at Bosch Mobility Aftermarket, and, even if you jump start it, without the alternator to recharge the battery as you drive, you’ll find yourself back at square one before long.”

How much does it cost to replace an alternator?

The cost all depends on the model of your car, if you install an OEM (original equipment manufacturer) part one or an aftermarket one and if you are doing the job yourself or through a shop. Just the part can run between $120 to more than $1,000.

“The labor will depend on your vehicle,” says Musson. “If you can change it yourself, your only cost is the alternator. If you have to have it, don’t, you could pay as much as an additional $800.”

What to know about buying an alternator

Instead of selling only to the carmakers, some manufacturers now sell new alternators through online stores. In many cases, you can buy a new alternator with a lifetime warranty for 30 percent less than the cost of a rebuilt one. So if you can live without your car for a couple of days, buy online.

How long do alternators last?

Alternators typically last between seven and 10 years, sometimes longer. The most common reasons alternators fail include damaged parts within, overuse, or engine oil or power steering fluid leaking into it.

Can I replace the alternator myself?

Yes. Replacing an alternator isn’t a complex task, but it does require a basic understanding of car mechanics.

“For all vehicles, this requires removing the belt,” says Chris “Moose” Pyle, and automotive expert with JustAnswer. “That in itself can be a difficult task since the belt tensioner is hard to access and under a lot of spring tension.”

Another common hurdle is not knowing how to route the belt once it is removed, so make sure you have a diagram, draw one or take pictures. “Also, on some vehicles, the alternator is replaced from under the vehicle, which make them the most difficult ones to do in your driveway,” says Pyle.

If you’re not comfortable doing it yourself, it’s best to take it to a pro to make sure it’s done correctly.

Even if you’re not confident replacing your alternator yourself, it’s a good idea to test it before taking it to a mechanic.