Overcharging batteries causing batteries to boil?

Tiny
AARON ZIMMERMANN
  • MEMBER
  • 2005 DODGE RAM
  • 5.9L
  • V6
  • TURBO
  • 4WD
  • MANUAL
  • 190,000 MILES
Hello, so I recently had a problem with my passenger battery boiling due to overcharging, I have read through a million threads and done a lot to self diagnosing and attempts to repair the problem. I have replaced all my batteries, the cables including the cross over cable, the alternator and cleaned all the connections I can see. The problem went away for about 2-3 weeks then yesterday my passenger battery started to boil again. When I check the voltage with the truck off both batteries are in the 12 volt range but when I turn it on the brand new alternator is pushing out 18v and i'm at a complete loss of where to go from here. Also my truck did throw a p0106 code for the MAP sensor but I don't know if that's related or not.
Sunday, April 18th, 2021 AT 4:25 AM

15 Replies

Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I'm Danny.

Just a few questions first. This replacement alternator was it a remanufactured unit or brand new? Was it replaced prior or was this a first replacement? It's voltage regulator is way to high putting out 18 volts. Normal output should never be over 14.5v . This guide should help

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Let us know and we'll go from there. Hope this helps and thanks for using 2CarPros.
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Sunday, April 18th, 2021 AT 4:49 AM
Tiny
AARON ZIMMERMANN
  • MEMBER
  • 7 POSTS
It was labeled a new one from AutoZone, I don't really trust remanufactured, lol. I don't know if it has been replaced before I bought the truck, but this was the first time I replaced it. After I replaced it, the batteries and all the cables if was putting out 14v and everything was peachy for a bit.
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Sunday, April 18th, 2021 AT 5:24 AM
Tiny
DANNY L
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Hello again.

Okay. How long ago was this replacement? Is it still under warranty and what brand alternator from AutoZone--- A Duralast?

Danny-
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Sunday, April 18th, 2021 AT 5:35 AM
Tiny
AARON ZIMMERMANN
  • MEMBER
  • 7 POSTS
It has only been maybe a month or 2 max since the replacement and I do believe it is a Duralast.
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Sunday, April 18th, 2021 AT 5:37 AM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

When you say you noticed the 18v output is that on the trucks instrument panel gauge or have you used a dvom - digital volt ohm meter on the alternator output pole?

Danny-
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Sunday, April 18th, 2021 AT 6:01 AM
Tiny
AARON ZIMMERMANN
  • MEMBER
  • 7 POSTS
The dash meter and my smarty tuner are reading around 12v, but if I use my dvom on the alternator its reading 18v.
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Sunday, April 18th, 2021 AT 7:07 AM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

Okay, that alternator is defective. The internal voltage regulator is ruining your electrical system by overcharging. It should never be over 14.5v I would suggest you return that alternator since it's only 2 months old a requests a new replacement. Hope this helps and thanks again for using 2CarPros.

Danny-
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Sunday, April 18th, 2021 AT 7:33 AM
Tiny
AARON ZIMMERMANN
  • MEMBER
  • 7 POSTS
Okay, is it possible that my ECU or PCM is bad and telling the alternator to push that much power?
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Sunday, April 18th, 2021 AT 8:02 AM
Tiny
AARON ZIMMERMANN
  • MEMBER
  • 7 POSTS
And what could cause my alternator to fail like that?
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Sunday, April 18th, 2021 AT 8:02 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I noticed you haven't been contacted in a couple of days. I hope you guys don't mind if I jump in.

First, I noticed you indicated using the DMM at that alternator. That is why you are seeing 18V. This vehicle's voltage is regulated by the ECM, which is after where you checked. You need to check it at the battery.

The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the ECM for diesel engines. The EVR is not serviced separately. If replacement is necessary, the ECM must be replaced. See pic 1 below for location. It's near the fuel filter.

The remaining pics include the directions and pics for replacement. I'm adding them in the event the ECM is bad. However, you really need to check at the battery for voltage. Checking at the alternator is bypassing the ECM.

I hope this helps. Let us know if you have additional questions. Also, we would appreciate it if you could let us know what you find. We're interested in knowing.

Take care,

Joe

See pics below.
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Tuesday, April 20th, 2021 AT 9:16 PM
Tiny
AARON ZIMMERMANN
  • MEMBER
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Hey, so I was getting 18v coming of the alt and at my passenger battery, which was making my passenger battery boil, I think I had a faulty stud on my brand new driver battery because I pulled them out and put 2 new ones in for 3rd time and now it's back to 14.5v across the board.
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Wednesday, April 21st, 2021 AT 3:10 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

That is good news. I was reading through this and just wanted to jump in. Regardless, if you are at 14.5v, that's perfect. If in the future you find that changes and both batteries are overcharging, chances are it is the ECM. Let us know and we'll help you through replacing it.

Take care of yourself and let us know if you have questions in the future.

Joe
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Wednesday, April 21st, 2021 AT 5:40 PM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

Glad to hear you were able to fix the problem. Let us know if this problem happens again. Thanks again for using 2CarPros and we will hope you will use our site again in the future when needed.

Danny-
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Wednesday, April 21st, 2021 AT 9:04 PM
Tiny
RPARKISON
  • MEMBER
  • 1 POST
  • 1996 DODGE RAM
  • V10
  • 2WD
  • AUTOMATIC
I have replace my alternator, the comp which contains the voltage regulator and my truck still is over charging and the gen lite is on. What next should I do?
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Wednesday, June 23rd, 2021 AT 7:08 PM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
Start by measuring the voltage on the two small terminal nuts on the back of the alternator, then holler back. One will have full battery voltage, the other one must have less but not 0 volts. If it is 0 volts, that wire is grounded somewhere on its way to the Engine Computer. If you find around 4 volts, the computer has control of the alternator field but it is trying to run it wide open. That could be due to a break in the voltage sensing wire going to the computer. That circuit is used for other things too so a break would cause other problems, but a corroded pin in the connector would still let the circuit work but the voltage would be low. The computer would interpret that as needing to increase alternator output.

The engine must be running when you measure those voltages. There will be no voltage there with just the ignition switch turned on and the engine is not running.

Caradiodoc
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Wednesday, June 23rd, 2021 AT 7:08 PM (Merged)

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