Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. How Does a Mechanic Check a Car Alternator's Volt Output?

How Does a Mechanic Check a Car Alternator's Volt Output?

alternator voltage Ovu0ng / Shutterstock.com

Have you ever wondered how a mechanic checks your alternator? It’s not something that has to be done all that often, because usually alternators are maintenance-free, and they can last for up to 12 years without needing repairs. When they fail, though, they have to be fixed or replaced, because your car can’t run on battery power alone – once the charge is gone, your car stops running.

It’s a good idea to have a mechanic test the alternator from time to time, especially if you’re seeing your “charge” icon come on and stay on when you start your car. This doesn’t necessarily mean you have a bad alternator, although it’s definitely an indication that something is wrong, so have a mechanic test your alternator.

How mechanics test the alternator

Mechanics uses a computerized charging system tester to check your alternator. This is called an AVR test, and it can show if there’s a weakness in the charging system, or if you’ll need to repair or replace your alternator. It can also identify problems like blown fuses, faulty wiring, a defective ignition switch, a loose drive belt, or other issues.

A mechanic could also perform a voltage test, which is designed to measure voltage in your battery with the engine running, and with it off. Voltage should increase when the engine is started, since the alternator delivers additional power. If it doesn’t increase, then there’s a charging system problem.

A bad alternator is usually due to one or more common problems. Sometimes, the contact rings or the carbon brushes become worn. Bearings can go bad (this could be the case if you’re hearing a whining noise from your alternator), or the voltage regulator could be damaged. Sometimes, it’s possible to repair your alternator. Other times, replacement is the only sensible solution. YourMechanic can help you identify alternator problems before they become severe.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Shutterstock.com Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...

Related questions

Q: Honda says bad usb device when I connect a device that has previously worked

Hello, thank you for writing in. Honda does not use a seperate fuse for some of their USB circuits. If your model does have a fuse, start by checking that. There are several other cases of issues with the Honda...

Q: Advice on working as a mechanic

I'm kind of unique because I learned from my grandfather, who was a mechanic at the corner of Texaco gas station in New York when I was a kid. So I learned hands-on from my grandfather. He wouldn't teach me...

Q: Charning issues, new battery and alternator

Hello there. There are a few potential causes for why the car would have charging faults even after the alternator is replaced. The most common would be the battery cable, shorted harness, battery, or a failed alternator. The first thing...