Car Won’t Start After Replacing Alternator – What’s Wrong?

When working on a vehicle's engine, you may encounter new problems, especially if you are replacing parts. Your car not starting can be caused by installing a faulty component, improper installation, and many more issues. With the help of experts, we will help you find out why your vehicle won't start after replacing the alternator.


A vehicle's alternator is an essential part that needs to be appropriately maintained. Below are the most common reasons your car won't start after replacing the alternator.

  • Dead Battery
  • Faulty Unit
  • Faulty Fuel Pump
  • Faulty Starter
  • Corrosion
  • Loose Connections


Finding where your problem is coming from can be a pain if you don't know where to look.  If you are not mechanically inclined, you should ask someone who's familiar with car components or get a mechanic to help you. For more information about your vehicle's components, keep on reading.

Car engine under the open hood, Car Won't Start After Replacing Alternator - What's Wrong?

Why Won't My Car Start After Replacing The Alternator

There are many reasons why your vehicle won't start after replacing your alternator. Most of these problems can be diagnosed with ease, while others will require you to have some mechanical or electrical knowledge.


Below are the most common issues that may be causing your vehicle not to crank or even start after replacing the alternator.

Dead Battery

Taking a car battery out of a truck

One component that relies on the alternator is the battery of your vehicle. When the car is running, the alternator provides power to the battery so that your battery will not lose charge. 


You may have a dead battery because of a few reasons. One of the most common ones is your battery has no charge. A dead battery is a common issue, especially if you have to change your alternator. This may mean that your alternator did not charge your battery, and that is why it is currently dead.

One way to fix this is to have the battery charged at a mechanic shop, auto parts store, or to idle your vehicle after a jumpstart. You can remove the battery and or have your current vehicle jumpstarted to have a mechanic charge it.

Since you have installed a new alternator, your vehicle should run fine after a jumpstart. Just remember not to shut off your car until you are at the recharging location because there is still a chance the car's alternator may not fully charge your battery.


Another reason could be that your car battery is completely dead. If your vehicle won't start and there is no power at all in the car, this could be the reason. You should check the date of your battery; it should say what year and month a mechanic installed it.


Batteries have an expiration date of around four years, so if your battery has exceeded four years, you are due for a new one. If you already got your battery checked or replaced a new battery and your vehicle won't start, this may not be the cause of your problem.

Faulty Unit

You may have replaced your alternator with a new one, but there is still a chance that the new alternator could be faulty. A faulty unit, like all components, still has a chance to break even when new. That's why you should have a warranty to help fix this problem.


If your new alternator acts up even when new, it is best to call the auto shop where you got it installed. Car components also have a warranty, but the time for replacement may differ depending on the store or unit's policy.


That's why you should ask the store or the mechanic if you can replace the vehicle component you bought from them if it breaks within a set period of time. Note that when a vehicle doesn't start, it is typically the alternator or the battery that has a problem.

Faulty Fuel Pump

Aside from the battery and alternator, other components may have broken down at the same time your alternator did. Another possible reason why your vehicle is not starting is lack of fuel.


The purpose of a car's fuel pump is is to deliver fuel into the engine. A few issues may be happening to your fuel pump if your car doesn't start.


One of these issues is if the filter is clogged up. Your fuel pump has a filter on it to help keep dirt out of your engine. Once the filter has clogged up, your pump will have difficulty supplying fuel to your engine.


Another reason could be your fuel pump is broken. A broken fuel pump can be due to old age or high vehicle mileage. If this happens, you should hire a mechanic to install a new one.


When something breaks or won't work correctly after installing a new component, we tend to look at the recently installed part. From there, we tend to forget the other parts that may not be directly affected by the new installation but still have the possibility of braking.


Coroded car battery

Corrosion can not only prevent your battery from delivering electricity, but it can also eat wires. Prevention of corrosion is essential since it may affect critical components of your car that may put you and your passengers at risk.


One spot that can have corrosion that will prevent your car from starting is your battery. A car battery has acid and a metal post where you connect wires to deliver electricity to your car's components. Once acid hits the metal post, this is where the corrosion will start.


Remember to disconnect the wires when cleaning the corrosion off the battery to avoid shock. You'll have to use water to help remove the corrosion. That is why there should be no wires connected to the battery when cleaning it.


You can't entirely remove corrosion once it starts, so you'll have to keep it at bay. Regular checkups can help you monitor the condition of the corrosion.

Loose Connections

When installing new car parts, there will be a time when you'll have to disconnect a few wires. Even though you are careful in reconnecting them, there may be one or two that could slip by you.


Check every connection to ensure they are secured, and you can also try reconnecting some of the wires you previously removed. Sometimes it's the simple things that we tend to outlook. That's why it is a good habit to double-check everything when reinstalling parts.


How Many Years Does An Alternator Last

Detail of an engine with an alternator in the foreground

After replacing your car's alternator, it is a good idea to know when it will need another replacement. An alternator lasts around 85,000 to 100,000 miles, or 7 to 10 years.


Using aftermarket parts can also decrease the life of your alternator. That's why you must still use OEM car parts when replacing components to maximize the lifespan of your alternator.


Also, pushing your vehicle a lot, such as driving on steep roads, can affect the lifespan of your alternator since the car will need more power. Regularly checking your components is a good idea because there may be signs that can help you prevent your components from breaking.

Do I Need A New Battery After Replacing The Alternator

Car battery under the hood

No, you do not need to replace the battery when you replace the alternator. Though these two components work together, if one breaks, it should not cause the other one to break also.


The most common problem you will face once your alternator fails is that your battery will get drained. If this happens, you won't need to replace the battery but get it charged again. But if your battery is past four years when you get your alternator replaced, it is a good idea to get a new one, too, since batteries have a typical lifespan of four years.

Final Thoughts

When your vehicle doesn't start after replacing the alternator with a new one, the two main components you should check are the battery and alternator. These two components work hand in hand. If one breaks or fails, the other component will suffer.


Other factors exist besides the alternator and the battery, such as wires, corrosions, and other vehicle components. Remember, even if a part is new, it can still be faulty. Also, if you are not mechanically or electrically inclined, it's best to get help from a mechanic or a friend who knows how to work with cars.


For more topics and tips, you can check out the following posts:

How Long Do Spare Tires Last? [And How Far Can You Drive On Them]

How Much Does It Cost To Install A Bull Bar In The US?

Can You Drive Your Car Right After Windshield Replacement?




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One comment

  1. Greetings!!

    Had a mechanic install a alternator/battery both new and truck still has starting issues.

    Mazda Tribute

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