Symptoms of a Bad Alternator

Reader Question

Hi Austin,

I think I might have a bad alternator in my car. Can you tell me what the common symptoms of a bad alternator might and how I can check it myself?


Hello there Danny, thanks for your question.

What should volts and amps be?:

A correctly operating Alternator should read 14.3 Volts and the amperage will vary according to the load.
Is there an easy way to test, if so how?
Most vehicles have a volt gauge and a quick look at that will tell you if the alternator is working. Along with the gauge there is usually a warning light that is representative of a battery.

If that comes on, your charging system is malfunctioning. The first check is a simple one. Open the hood and make sure the belt is still on the alternator. Once you have verified the belt is on and turning with the engine a Multimeter on the large lug on the rear of the alternator will quickly tell you what the voltage is.

If it is not at 14.3 volts, turn on the headlights and raise the rpm to 1500 and recheck the voltage. If it is not charging turn the engine off and check the voltage again. If the voltage reads about 12.2 that is ok, that will be the surface charge of the battery.

If it is not at battery voltage there is a problem with the circuit between the battery and alternator. If you have battery voltage and it is still not charging, check your fuses. If all fuses are good then you should remove the alternator and have it checked at a parts store.

Most modern Alternators are self regulating, which means that the regulator is part of the alternator. Older vehicles have a separate regulator which can go bad. Most parts stores will check your alternator and regulator for free and tell you which one you need.

About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."