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

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

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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.


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Chris

21 years of experience
1861 reviews
Chris
21 years of experience
Mini Cooper Clubman - Brake Pads Replacement (Rear) - Silverado, California
He arrived early, went straight to work, and it should have been quoted higher as it’s a Mini which takes longer than the average break job. He didn’t try to get more than the quoted amount. He even set out to replace a running light for me when he was finished. I thought there would hard sales telling me I needed more work but there wasn’t. Because he didn’t try to sell me more work, I will use him again. When I hired a mechanic I don’t want a salesman. 
Land Rover Range Rover Sport - Brake Pads Replacement (Front) - Irvine, California
Chris again has provided great Service. Everything was great. I was very happy with the work and will definitely have him return for any other work.

Bryant

11 years of experience
408 reviews
Bryant
11 years of experience
Ford Fusion - Brake Pads Replacement (Front, Rear) - Indianapolis, Indiana
Bryant has done great work on my car before, the latest work is no exception. He's very flexible, and goes the extra mile to get you back on the road.
Scion iA - Brake Pads Replacement (Front) - Carmel, Indiana
This is my first time using this service. I am very happy with it. Bryant was very knowledgeable and did quality work. I will use this service more regularly.

Edmar

21 years of experience
184 reviews
Edmar
21 years of experience
Chrysler 200 - Brake Pads Replacement (Rear) - Euless, Texas
Edmar always does a very good job. He's done a few different things on my car the last two years. Each job was performed very fast and top quality. Thank you once again.

Mazyar

7 years of experience
255 reviews
Mazyar
7 years of experience
Jaguar XF - Brake Pads Replacement (Rear) - Lawrenceville, Georgia
He was early, courtesy and actually helped me save some money since i didn't need all the work that i thought i needed done. Honest guy. Very knowledgeable. Great attitude.

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