How To Test An Alternator In Four Easy Steps

How To Test An Alternator In Four Easy Steps

Your car’s alternator is an important element in its design because it works with the battery to produce power for the car’s electrical components, such as the exterior and interior lights and instrument panel.

But it’s not always easy to know if your car’s alternator is in good condition.

What do you need in order to test your alternator? You’ll need to ensure you have a voltmeter or multimeter handy in order to give your alternator a checkup.

However, you can also check your alternator in other ways. Here’s what to do. 

How To Check Alternator In Four Easy Steps

Step One: Start By Purchasing A Voltmeter


This is not an expensive device to purchase as you can probably find one for less than $20.

If you don’t have a voltmeter and you don’t want to wait to buy one, you can use a multimeter. Both of these will enable you to measure the alternator voltage.

Step Two: Check Your Car’s Battery


Since the battery starts your car and then activates the alternator so that the battery gets the power it needs, you should check that your battery is working properly.

It’s sometimes easy to misdiagnose a car problem as being inside the alternator instead of the battery, so it’s important to rule out the battery.

  • Turn off your car and open its hood so you can connect the voltmeter to the battery. 
  • Make sure you connect the device’s red lead to the positive battery terminal and the black one to the negative terminal.
  • The voltmeter will give you a voltage reading. It should be 12.2 volts or more as this will indicate that it has the power to give to the alternator. If this is not the case, the battery needs to be re-tested or changed.

Step Three: Put The Battery Through Other Tests


Keep the car’s engine running and rev it to 2,000 RPM so that your alternator will work. You must then test the battery again with the voltmeter.

The reading should be a minimum of 13 volts. If the RPMs are what’s making the voltage go up and down between 13 and 14.5 volts, the alternator is in good condition.

If it remains at the same level or decreases, these are signs that the alternator could have a problem.

Now, test the battery for a third time with the radio, AC, and lights on inside your car. This will show you how well or poorly the alternator is providing power to the battery.

The voltage reading needs to stay above 13 volts and you should aim to keep the RPMs at 2,000 for the duration of the test.

Step Four: Test The Alternator Gauge


Make the car engine run at 2,000 RPM and then turn on the AC blower fan, headlamps, and other accessories inside the car that use power from the alternator.

If the voltmeter is giving you a higher reading when the engine’s running than when it’s not, then you know that it’s charging properly. 

Other Signs That Your Alternator Has A Problem

Other Signs That Your Alternator Has A Problem

While a dead battery is a common sign that your alternator has a problem, there are other signs that it’s malfunctioning.

  • Your warning lights are on: The warning light on the dashboard that looks like a battery might come on if your alternator has a problem, but sometimes the words “GEN” or “ALT” will also show up, depending on your specific car.
  • Your headlights are acting up: If your headlights are dim or flickering, these show that your alternator is malfunctioning because it doesn’t have the power for these accessories.
  • Your power windows and seats don’t work well: If these are working slower than they should be or aren’t working at all, this points to the alternator battling. You might also find that the car’s internal lights or radio aren’t coming on.
  • You can smell burning rubber: This smell is associated with the belts in the car that your alternator works with, and if they’re not functioning properly they will produce more friction. This makes them reach a very high temperature, which is what’s responsible for that smell. Similarly, if you smell something akin to an electrical fire, the belt might be slipping.
  • You’re hearing weird sounds: If you hear rattling, whining, and grinding while you drive, they’re usually associated with an alternator that’s not in a good condition. A high-pitched sound can point to a problem with the bearings.
  • Your radio sounds weird: If you have a radio in the car, put it onto an AM band that has no music. If you can hear that it becomes fuzzy or you hear a whiny noise when you put your foot on the gas, the alternator is probably why. 

Related Questions

Does a bad alternator affect the car’s spark plugs?


A bad alternator won’t be able to give power to the spark plugs, and when this happens you might find that the car has trouble starting or stalls out of the blue.

How long can you drive with a bad alternator?

This depends, as you can drive for as long as your car’s battery has enough power. Bear in mind that a faulty alternator could damage a healthy battery.


If you’re worried about the health of your alternator, you’ll be glad to know that you can test it in a variety of ways.

In this article, we’ve looked at how to use a voltmeter to check your alternator health as well as what you should be on the lookout for when driving your car as there are some clear signs that your alternator is malfunctioning.

Best of all, you can do these tests without the use of a voltmeter.


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