Voltmeter fluctuates between 8 and 18

2000 model Dodge Dakota. Volt meter fluctuates between lowest and highest reading. When I am stopped or idling reading is between 8 and 13, when driving 14 and sometimes up to 18. Readings are lower when lights, ac, etc. are on. When voltmeter reading are not normal there seems to be a whirring coming from engine bay where alternator is. I think the alternator has gone bad but not 100% sure. New to cars can I get some advice?

It sure sounds like an alternator problem, but it could be the voltage regulation circuitry, which is in the ECM. Verify the voltage readings first. Also be sure your battery terminals are clean and tight.


Concur , sounds like an alternator problem. I doubt it’s this problem, but first step is to make sure the accessory belt isn’t slipping on the alt pulley. Also good idea to verify the problem isn’t w/your volt meter. It’s possible the alternator and charging system are working fine and the only problem is the volt meter. Are you using the volt meter on the vehicle’s dashboard display, or a lab volt meter? What does your battery measure before the first start of the day? Measured with a lab volt-meter at the battery terminals.

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Sometimes the signal wire to the ECM gets damaged causing ECM confusion.