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Inconsistant voltage reading

4K views 6 replies 5 participants last post by  Ingrdude 
#1 ·
For about the past 2 -3 weeks I have been having a problem with the electrical system in my 2004 Dodge Ram 1500.
The voltage reading on the voltage gauge varies: Normal: needle straight up and down and center on the gauge, Low: needle off to the left toward "L" and finally None: needle rests on the pin next to the "L". Any of these readings can happen upon starting, idle or full highway speed.
I have replaced the battery and the alternator. I purchased an external voltage meter and connected it in. It reads consistent with the dash gauge, ~14v, ~12v or not registering. I have had the new battery and alternator checked. I have also checked the connectors. I also cleaned the battery terminal connections when I replaced the battery.
On a semi-related note. I just replaced the serpentine belt and the tensioner bearing. I don't hear a squeal like I'm getting belt slippage.
I have heard about the Battery Temperature Sensor. Not sure it that would cause this particular issue. I guess at this point another $35 won't matter.
The worst part is it is inconsistent so just when I think I've done something to fix it, it comes back.
I'm not sure about the complete history of this truck. It was a replacement vehicle after Harvey.
Thanks for your help on the front side of this.
 
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#3 ·
Don't concern yourself about the Battery Temperature Sensor, it is just a heat sensor mounted in the battery tray that barely touches the bottom of the battery to detect temperature extremes

Your alternator has a internal voltage regulator

I can only suggest that you connect up battery to a battery charger for at least 3 hours after disconnecting the Negative post on the battery, doing that should give your battery a Deep Charge

The Rams alternator, because of the internal voltage regulator will not put out regular charge once the battery gets below a certain point, because there is a built in Safety cut off so the battery can Not over charge. That safety cut off won't allow the battery to get a Full Charge
So the alternator is only capable of replacing a surface charge, it will not give the battery a deep charge & your battery needs to be fully charged.

Batteries sold in stores are only given a surface charge, which is OK IF you had a external voltage regulator
 
#4 ·
Covered this for a couple members the other day. The voltage is regulated by the pcm, sometimes that goes bad and can't be fixed seperately and requires a new pcm. There is also a work around fix by making an external voltage regulator, which is cheaper than a new pcm. The video link explains how to make an external voltage regulator and the description of the video has a link to a detailed write up. The gen3's pcm voltage regulator seems to be its weak point.

https://youtu.be/HtB3g1kk8Rg
 
#5 ·
GTyankee, I will try the deep charge as you suggested. Makes sense about over charging the battery, just a shame it's not as easy and changing out a battery like it used to be.
Chilliin, Will take a look at your link. Hope I don't need to get to that point, but appreciate the knowledge to have in my back pocket if needed.
 
#7 ·
Sorry it has taken so long to follow up on this, had a logistics issue. I also want to say thanks to everyone who has replied to my question and is helping me with this.
I set a battery charger on the battery over night. Still had same issue.
I replaced the PCM. Still having nearly the same issue. Now my external volt meter reads ~12 volts, but the dash voltage meter reads within the range (on the low side so could be 12 volts) but then it will just drop down to 0.
The voltage reading on the external volt meter doesn't change when I increase the draw: headlights, windshield wipers, A\C.
So I now have a new battery, alternator and PCM. Not too many more parts to replace I would think.
 
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