Recently the voltage on my 2000 Dakota (3.9L, 45000miles) has been spiking to 18V on the gauge. If you turn the truck off and wait a minute then restart, the problem goes away. The truck seems to run fine either way. The problem happened 2-3X in the past two years but now has happened 4X in the last week. I am guessing that the voltage regulator is bad. Is this in the alternator? I have changed alternators in cars before so I would have no problem swapping this out but want to make sure that the regulator is not somewhere else and so changing the alternator will not help.

Any help appreciated.

Thanks,
Pete

 

you're going to need to do an alternator draw test. a garage can do it for you or autozone can too

 

The main voltage regulator is located in the PCM.

I don't think this is your problem tho. I would place some good money on the rectifier bridge diodes in the alternator. Although the PCM regulates internal voltage the alternator is on free roam. Not to mention voltage like that entering the PCM would fry it in my opinion.

If I were you I'd shoot strait into buying a new one (no rebuild).

Also have the battery load tested to ensure that it is functioning normal.

 

Pls check your battery connecton. The alternator charges the battery so it has hight output than the battery voltage. If you remove the battery from the circuit, you have a lot lower load and your voltage WILL jump.

 

Agree on the battery terminals. I've seen badly corroded ones cause the spike.

 

+1 on the corroded terminals. Anything that would cause a voltage drop in any of the battery voltage wires going to the controller can fool it into thinking the output voltage from the alternator is lower. The PCM cycles the alternator constantly on and off to regulate voltage.