Skip the auto shop - Our mechanics make house calls

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

Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...


Related questions

Q: Having a hard time with the doors locking or not locking

Keyless remotes for the Volkswagen Jetta have been known to act erratically when the batteries are getting low or the remote is defective. First, try replacing the batteries in your remote and verify that the problem is fixed. If problem...

Q: What do I need to do to become a mechanic?

Today's vehicles are complex. To be a good mechanic, you need a basic understanding of all the core educational requirements including English and math. A good understanding of computers, both how to use them and how they work, is also...

Q: Battery is not charging properly

This may be a sign of a weak battery, a failing voltage regulator or failing alternator. As you may know, the alternator is responsible for charging the battery while the engine runs by generating amperage and recharging the battery while...