How To Test A Car Alternator: 5 Steps

Posted 9/20/2018 by Tyler Rodriquez

If you are having charging problems or see a battery light pop up on your dash, the problem may be your alternator. Let LMR show you how to test a car alternator in 5 easy steps.

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When your car's charging system is not performing up to par, you run the risk of being left stranded on the side of the road. When you see a battery light pop up onto your dash, you know that there is some type of fault in your charging system. If your battery is fairly new, the most likely culprit is your alternator. Follow along as LMR walks your through the quick and easy steps on testing your alternator.

How To Test An Alternator

  1. Remove battery terminals and make sure these are 100% clean from and buildup of corrosion. Clean these to ensure proper continuity for the charging system. Reconnect for testing.
  2. Test the battery voltage, at rest this should read between 12.5 and 12.8V on average. If the batter is low, then charge the batter to meet these specs.
  3. Check over all vehicle grounds to ensure these are up to par.
  4. Inspect for proper belt alignment and any possible belt slippage, these can affect overall output of the charging system.
  5. Test the battery and look for 13.5V-14V with the engine on and all accessories off including lights, a/c, and radio. This can be done at the battery terminals with a quality digital volt and ohm meter. This should be a normal reading for these setups. If you do not have access to a DVOM, then you can remove the alternator from the car and most local auto parts stores will test these for free.
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