Jump to content
  • Sign up for FREE! Become a GM-Trucks.com Member Today!

    In 20 seconds you can become part of the worlds largest and oldest community discussing General Motors, Chevrolet and GMC branded pickups, crossovers, and SUVs. From buying research to owner support, join 1.5 MILLION GM Truck Enthusiasts every month who use GM-Trucks.com as a daily part of their ownership experience. 

2005 GMC Sierra 1500 Electrical Issues

Recommended Posts

I was having electrical issues on my 2005 GMC Sierra 1500, which is at 197,000 miles. The issues were things like pulsing lights (interior and exterior and low voltage fluctuation (14.0v to 11.8v) so I replaced the alternator with a premium 160amp remanufactured one from CarQuest. Now my voltage seems high, sitting at 14.9v-15.2v during idle. The pulsing went away, but now it pulses when I rev the engine. I will leave it at about 1500 RPMs and it will steadily pulse until I release the gas. Is this an issue with the alternator or something else?

Link to comment
Share on other sites

Is the battery light still on?  I had an alternator problem with a Trailblazer, battery light would not go off, connections were tight.  I checked continuity of all the connections to their next assembly and found that the wire carrying the pulse width modulation signal (PWM) was open.  The fault was fairly close to the connector and I fixed it with a pigtail I cut from a unit in a junkyard.


You mentioning pulsing also makes me wonder if it is in the PWM circuitry, but if it is, it is likely not an open PWM wire as that would cause the alternator to give max output all the time.


Good luck and let us know.


Another member had similar problem, but he never followed up with his fix: 


Link to comment
Share on other sites

Jordan... just for the heck of it run a temporary ground wire from battery negative to the truck body and see if there is any difference. I've seen this type of problem on older vehicles where the factory grounds looked good but were no longer doing the job. Won't cost you anything to try.

Link to comment
Share on other sites

Well after driving the truck for a couple days, the voltage seems to start out high - 14.8 to 15.2 volts, and then slowly drop after about 25 minutes down to 12.8 and hovers between 12.8 - 13.1v. If I turn on the head lights it slowly climbs back up to normal 14.3-14.5v. I read in the manual about the RVC (Regulated Voltage Control) and I'm wondering if it's just part of that?

Link to comment
Share on other sites

A good description of the charging system can be found in this post from an Avalanche club.




Another thing that could cause the flickering is the battery.  Just because a battery is charged to 14vdc doesn’t necessarily mean that it can keep providing current under load if it is unhealthy.  Of course this could also just be some random electrical component someplace in your truck.


My 05 has the works, heated seats, electric fans, nice radio, and I haven’t noticed any flickering.  If you’re issue was not intermittent, and you were closer- we could just swap batteries for a bit.  If that didn’t work, you could start pulling fuses to non-essential circuits until you noticed the flickering diminish.  There is the off chance that it is in one of the control modules.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Similar Content

    • By JeffOBS
      I am looking for some detailed electrical drawings/schematics for a 1994 Silverado K1500. I have the Hayne's and Chilton's manuals but may need more information about the electrical system. I had a shop do a LS swap in my son's 94. They did a great job installing the 5.3 with the mated transmission. The motor runs great and no issues with the transmission. But there are items that are not working that were working before the swap. The shop didn't give me an upfront estimate for the swap and was billing me an hourly rate so I'm doing the rest of it myself. I have used the search bar here with limited results. I am a new member here and I'm having a hard time navigating this site. Plus, what's up with all these ads that are everywhere? Thanks in advance for your help. 
    • By John Crouse
      Hi All. 
      I have got a real puzzle. The volt meter (analog) on my dash when cold reads just under the 14 volt mark. As it warms up it drops eventually to just above the red zone. I have changed out all my cables with heavy duty cables, cleaned all grounds I could find, being that both were old anyway, changed alternator and battery for top pole battery., swapped out Ecm (swapped back), and still the same. Here is the real puzzle for me. I have checked with my multimeter the continuity of the battery cables and when running, tested the volts. With multimeter everything is good to go and reads 14 volts. So guys, what do you think? 
    • By Matthew J M Devildog Thompson
      My brake lights stopped working intermittently. Now they are permanently out. Checked the bulb, good. Checked the wire, good. What could be causing this?
    • By qoconnell
      This is my first post so sorry if I’m all over the place. I’ve had my 2014 Sierra slt for about two years now. I got it with 116k miles and I’m at about 174k right now. Since the day I’ve bought the truck it’s been nothing but issues. You name it, it’s happened. Four separate water leaks (sunroof, gps antenna, third brake light, and cab vents), 2 transfer case control modules, problems with the power steering going out, brakes going out at low speeds. A couple of months ago my transmission went out and it also needed various other repairs totaling over $20k. Now my park assist sensors don’t work, my rear doors don’t open from the inside and also don’t lock from the outside, reverse lights and camera don’t work, and it constantly dings at me to service my trailer brake system (seriously, it chimes at me about every two seconds as I’m going down the road, telling me to service the trailer brakes). I’ve gone through and checked every ground I can find and nothing helps. Today I went through every single fuse and relay in the truck. I found a couple of blown fuses and replaced as needed, but still no change. I’m at a loss for what to do at this point as I’m stuck with the truck after all the money I’ve sunk into it. Does anybody maybe have any solutions to any of these problems? I’m desperate for answers, anything helps.
    • By Cory Warburton
      After recently swapping out my alternator, my truck lights are slightly dimming repeatedly. It's especially noticeable when I turn on the dome lights. Is it a grounding issue? The alternator doesn't physically touch the metallic base at all, but seems to be grounded only via the two bolts that hold it up and in it's right place. Should I take it off and sand any metal that connects from the bolts to the alternator?
  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Forum Statistics

    Total Topics
    Total Posts
  • Member Statistics

    Total Members
    Most Online
    patrick spires
    Newest Member
    patrick spires

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.