test alternator of car

To test your car alternator, do the following:

  1. Check your car battery cables. I’ve seen it many times, people think their alternator is bad, but it turns out to be loose or corroded battery terminals.

    Wiggle the negative and positive cables back and forth, make sure they are tight.
    If one of them is loose or there is any corrosion, loosen the retaining bolt and remove that terminal cable.

    Using a battery cleaner wire brush, scrape the post to make sure all rust and dirt is gone.
    Then, attach and tighten the cable and start your car to see if the problem is gone.
  2. If the battery cables look good, test the alternator using a multimeter. A simple one will do, see below for recommended.
    Turn the multimeter on to DC Volts at a range greater the 15. (V _ 20 is fine)
  3. Start the car.
    (If you had to jump your car to get it started, be sure to disconnect the jumper cables)
  4. Next touch the Black probe to the Negative battery terminal, and the Red probe to the Positive terminal of the battery.
  5. Read the voltage on the multimeter, you should see about 14 volts if the alternator’s charging system is working. If you see less than 13 volts, you could have a bad alternator.
Car starter battery voltage measured with multimeter. Voltage above 14 volts as the car alternator is charging the battery. Alternator is working well.

NOTE: When the car is not running, the battery should read about 12.6 volts when fully charged.

Best Multimeter to Test an Alternator

I use the following multimeter to test the battery and car alternator electrical system:

Etekcity - MSR-R500 Digital MultimeterCompared to other multimeters in the U.S. market, this gadget has special adjusters for voltage and temperature. If you seek overload protection, this stylish black machine can fit your requirements.


A wire brush to clean the battery terminals if needed.

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