2005 GMC Sierra 1500 Electrical Issues

[Jordan Walter]

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?

[Jordan Walter]

I have checked all the connections and grounds and they seem to be fine.

[EightTrackHits]

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: 

 

[Jordan Walter]

The battery light never came on.

[Mr. Z71]

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.

[dna9656]

As has been mentioned before; if it's weird and electrical CHECK THOSE GROUNDS!

[Jordan Walter]

I already mentioned that I checked the grounds and cleaned the connections.

[EightTrackHits]

By steadily pulse, you mean that the pulsing or flickering is at a fairly constant frequency, correct?  Not random?

[Jordan Walter]

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?

[EightTrackHits]

Yes, the changing voltage levels that you are describing is normal, but the discernible flickering or pulsing of interior lights isn’t.  Is that still happening?

[EightTrackHits]

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

 

https://www.chevyavalanchefanclub.com/cafcna/index.php?threads/lights-flicker.52489/

 

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.