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How To Test And Check Your Alternator At Home

Master This Easy At-Home Test To Make Sure Your Alternator Is In Top Working Order

How To Test And Check Your Alternator At Home

The alternator is an important part of any vehicle. After the battery starts the car, the alternator recharges your battery to keep your car running smoothly. And it helps keep all the other electronics in your vehicle powered while the car is on. This guide will teach you how to test your alternator at home, so you can make sure it is functioning at top capacity.

Five Steps To Test Your Alternator At Home

Eventually, like every part of a car, your alternator will fail. Every car is different. Sometimes your alternator might die at 80,000 miles. Or, if you’re lucky, it could last until more like 150,000 miles. Knowing the warning signs of a failing alternator and regularly checking its condition can help you stay one step ahead of a dying alternator.

testing an alternator

How to Test Your Alternator

1. Collect your tools.  You will need something to read the voltage/amperage of your battery and alternator. A cheap multimeter or a voltmeter will be able to test your alternator without hurting your engine. Set your multimeter to DC volts.

2. Turn off your engine. You will first need to get a base voltage reading from your battery and will need to do this while the engine is off.

3. Test the battery voltage. Touch the black meter lead to the negative battery terminal and the red meter lead to the positive battery terminal. Make sure that your battery terminals are clean, and you have a clear surface where you can get a solid point of contact for the lead. Your reading should be around 12.6 volts. If the voltage is lower than 12 volts, the issue might be with your battery. If this is the case, you will likely need to charge or replace your battery before you will be able to accurately test your alternator.

4. Turn on your engine and test the voltage again. The meter should read between 14.2 and 14.7 volts without any lights or electronics on. If it is lower than that, you may need to replace your alternator. If it is above that, your alternator may be overcharging your battery.

5. Test the load voltage. If you have an assistant, have them rev the engine to about 2,000 RPM while you monitor the voltage reading. Or if you are on your own, with your car still running, turn on your radio, lights, and any other electronic accessories and check the voltage reading. Though you will likely see a slight drop in the voltage with this added stress on the battery, the voltage reading should not drop below 13.0 volts.

If your voltage readings are outside of these ranges, check to make sure that the battery leads are securely connected to the terminals, that the wires around your alternator are all plugged in and in good condition, and that your alternator belt is tight. If after that, your voltage readings are still outside the standard range, you should consult with a professional mechanic on the next steps.

Frequently Asked Questions

Can you check your alternator while your battery is disconnected?

This is not recommended for a couple of reasons. Disconnecting your battery if your alternator is functioning properly can fry the electronics in your car. Without the battery as a buffer, the alternator can put out a lot of power, possibly too much for your electronics to handle.

Also, your alternator can put out enough power to keep your car running when you disconnect your battery, even if it is not doing well. This can give you a false-positive result for your test.

Generally, it is better to avoid this method completely and stick to the safer method of using a multimeter.

Can a bad alternator ruin a battery?

The short answer is yes. When your alternator is not working, your battery will not be able to charge. When a battery gets drained down 100%, the battery may tap into its reserve capacity. This can damage the battery’s performance and could destroy your battery.

If your battery drains, and you jump start it and it dies again soon after or doesn’t hold a charge, you may have a damaged alternator. You should also check your battery as it may need to be replaced.

How can you tell if it is your battery or your alternator?

Some signs of a dead or dying battery:

  • If your dashboard lights are dim, your battery could be dying.
  • The cranking of your car sounds sluggish or clicks when trying to start your car.

Some signs the alternator is failing:

  • Dim or fading interior lights
  • Headlights get brighter while accelerating but dim when not accelerating.
  • A squealing sound coming from the engine that gets louder when electronics are being used.

Ilana Newman
About Ilana Newman

Ilana Newman is a writer, photographer, and life long learner. Born and raised in the Pacific Northwest, and recently relocated to the desert and mountains of SW Colorado, she spends her free time climbing, running, and skiing in the mountains. She is passionate about sharing stories that can impact lives.