Jump to content



Photo
- - - - -

2002 GMC Sierra Alternator Voltage Regulator Problems

alternator regulator voltage

  • Please log in to reply
7 replies to this topic

#1 Kirkathon25

Kirkathon25

    Enthusiast

  • Member
  • 163 posts
  • Gender:Male

Posted 07 November 2012 - 04:53 PM

I have a 2002 GMC Sierra 6.0L 2500HD that i am trying to sell. The alternator went on it last week so i replaced it with a reman that turned out to be bad, it had low voltage coming out of it when i tested it (3.5-4V). They replaced that one with the same thing and tested it first to make sure it was good before handing it over. I installed that one and am having the same problem. The truck runs until the battery dies with no codes with the alternator averaging 3.5V of output according to my voltmeter. I am getting relatively pissed about this since i have replaced many an alternator and have never had so much trouble. Any help would be appreciated, cant find any threads that are specific to this problem.
2002 GMC Sierra 2500 HD SLE 6.0L with K&N Cold Air Intake, towing mirrors, LED Clearance lights. "You aren't lost if you dont care where you are"
Pewter Metallic Truck Club Member #5
Posted Image

#2 scooby5121

scooby5121

    Enthusiast

  • Member
  • 427 posts
  • Name:Eric
  • Location:Ontario
  • Gender:Male
  • Drives:08 GM 6L CrewCab Dually 4by4

Posted 07 November 2012 - 04:58 PM

Has to have approx. 14.5Volts average output.
Scooby

#3 Kirkathon25

Kirkathon25

    Enthusiast

  • Member
  • 163 posts
  • Gender:Male

Posted 07 November 2012 - 05:04 PM

Yeah i know, i dont know what could possibly be the problem, all wires are properly hooked up and not corroded.
2002 GMC Sierra 2500 HD SLE 6.0L with K&N Cold Air Intake, towing mirrors, LED Clearance lights. "You aren't lost if you dont care where you are"
Pewter Metallic Truck Club Member #5
Posted Image

#4 Kirkathon25

Kirkathon25

    Enthusiast

  • Member
  • 163 posts
  • Gender:Male

Posted 07 November 2012 - 07:00 PM

Does anyone know how to test the voltage on the plug for the alternator excitor? i think that the problem might be with the wiring for the regulator since i just put an alternator out of another truck that i absolutely know for sure works flawlessly and got the same problem. The plug itself has two wires running into it a brown and white.
2002 GMC Sierra 2500 HD SLE 6.0L with K&N Cold Air Intake, towing mirrors, LED Clearance lights. "You aren't lost if you dont care where you are"
Pewter Metallic Truck Club Member #5
Posted Image

#5 GMmytruck

GMmytruck

    Enthusiast

  • Member
  • 4 posts
  • Name:Bryan
  • Gender:Male
  • Drives:Chev 6.5TD/GMC 6.0

Posted 07 November 2012 - 07:01 PM

Had this problem in an old ford. :throwup:Took it in 3 times with the same problem. 3 alternators. I told them it can't be the alternator. They said their big 'magic' tester didn't lie. I finally ended up taking it to a small repair shop and the mechanic had a small hand held tester. He checked it for a minute or two and ended up pulling hard on one of the wires in the wiring harness and lo and behold it was broken. He fixed the wire and no problems after. Hope this helps a little.

#6 Kirkathon25

Kirkathon25

    Enthusiast

  • Member
  • 163 posts
  • Gender:Male

Posted 08 November 2012 - 12:26 PM

The wire seems tight in the plug however i just tested the voltage coming out of the two wires on the plug and there is voltage coming out of the brown wire but not the white, what i am unsure of is if this plug is ac or dc power? if the plug regulates voltage then i believe it is ac.
2002 GMC Sierra 2500 HD SLE 6.0L with K&N Cold Air Intake, towing mirrors, LED Clearance lights. "You aren't lost if you dont care where you are"
Pewter Metallic Truck Club Member #5
Posted Image

#7 Kirkathon25

Kirkathon25

    Enthusiast

  • Member
  • 163 posts
  • Gender:Male

Posted 19 November 2012 - 03:33 PM

Ok, its been weeks but i have found something out that might help, but i have no idea what it means. If i connect the alternator directly to the positive terminal it works great. The contacts inside that red box are all clean and the original jump wire from the alternator has continuity so i have no idea why it wont work hooked up that way. The only way the alternator charges properly is when my wire connects the positive terminal of the battery to the alternator directly.
2002 GMC Sierra 2500 HD SLE 6.0L with K&N Cold Air Intake, towing mirrors, LED Clearance lights. "You aren't lost if you dont care where you are"
Pewter Metallic Truck Club Member #5
Posted Image

#8 citydriver

citydriver

    Enthusiast

  • Member
  • 794 posts
  • Location:Buffalo, NY
  • Gender:Male

Posted 20 November 2012 - 07:52 PM

Check for voltage drops across the cable connections, connect the gound probe of a multimeter on the negative battery terminal, then check the voltage of the battery, then work your way down the system to the alternator. The voltage should be the same across the system. You can do this with the ignition ON and the engine OFF( not running ) Check all cable connections and fuses.

Once an ASE Master Tech,Now a Back Yard mechanic w/lots of expensive tools!

2013 GMC 2500HD Crew Cab Standard Box  SLT Z71............ work in progress........

2 weeks ago I couldnt spell TWUK DRIVER..now I IS one!






1 user(s) are reading this topic

0 members, 1 guests, 0 anonymous users