Strange electrical issue 2012 Sierra

BigBlockBurban454 · January 4, 2024

I am new to this forum, so I apologize if I have placed it in the wrong area.

My work truck for my company is a 2012 gmc sierra 1500 ls with the 5.3l. This truck was plauged with electrical issues since I bought it 3 years ago, all of which I thought I fixed being a shade tree mechanic my whole life and an electrician by trade.

A few days ago, I went to fire up the truck in the morning. I put the key in run for 3 seconds as I always do, and attempt to crank with the dash fully lit up. This time the second I put the key in crank, I heard a click and the truck lost ALL power. Pull the key out, put it back in, nothing. No dash, no chime, not even power to the cigarette lighter. I pulled the negative cable, reconnected, and all was normal.

The following day the same thing happened. Pulled the negative and reconnected, all good. Went to the gas station, did it again when trying to start. But this time, power came back when I removed and reinsert the key. All good.

The following day, started just fine in the morning. Same deal as the previous day, wouldn't start after gassing her up. Pulled the negative and reconnected, still no power. I had to pull and reattach the negative 3 times before I got power back and it cranked just fine.

At this point, I'm using the different scenarios to try and narrow down the problem. But today, it was really strange.

When leaving my jobsite today, I noticed that as soon as I put the key in accessory, I lost all power. I have a Bluetooth receiver for my stock radio, plugged into a constant hot cig lighter socket. The charging light was on until the key goes to accessory then it went dead. I pull the key, power comes back. Put the key back in and turn to accessory, loose power again. I did this about 15 times, same result. If the key was turned at all, I had no power to anything. With it off, I did have power to constant hot systems. I pulled the battery negative 5 times to finally get it to maintain power with the key turned, and finally it started completely normal.

Anybody have any ideas? I have 2 optima yellow tops less than 6 months old. There is absolutly zero corrosion on any major wire connections, and all connections are tight and adequate. I checked with my ohm meter.

I did notice today when I shut the truck off, I heard a pop come from the speakers. Truck ran no issues for the whole drive, but when I shut it down it killed power to everything much like when I attempted to start it.

I was thinking ignition cylinder, but zero power with the key pulled does not support that. I would really appreciate any input for this!! Like I said I am an electrician by trade, but automotive is quite different with computers and what not involved

2012 GMC Sierra LS Z60 5.3l LC9 4x4

1993 K2500 Suburban Cheyenne 454 4x4

BarryKH · January 4, 2024

I have found in my 60 years of shade tree mechanic work, that when I have an issue like you are describing, the very first thing I do is give the cable connectors and the battery terminals a very good cleaning. Although they look clean and you don't see any corrosion, there is a gray film that develops on them that causes that. Clean them with a wire brush, the battery and the cable ends, reconnect them good and snug, and I spray my with battery terminal protector I get from the auto parts, and it does a great job preventing this. When you can no longer see the red tint on the terminals, clean them again and respray with a light coat. I hope this helps. Many issues like yours are caused by clean looking terminals. Just my experience that I've had all these years.

diyer2 · January 4, 2024

Clean until shiny, use dielectric grease, coat all parts.

asilverblazer · January 4, 2024

Check all grounds... confirm by using jumper cables to go straight from battery negative terminal to body, engine, frame, etc.

BigBlockBurban454 · January 4, 2024

I have gone trough the battery connections and cleaned them up well, but I will certainly give it another go BarryKH. And I like the dielectric grease idea diyer2, not sure why I never thought about it. I use it all the time for electrical connections at work! I've been planning the big 3 upgrade as I want to install a 2000w inverter in the truck, so maybe I should just go ahead and do it because that would mean all new primary connections.

I also have ohm tested the ground between battery and block, battery and body, and battery to frame. They all test out good. But I like your idea asilverblazer using jump cables to introduce a new ground path for testing. I will try this next time she doesn't have power before I mess with the battery at all, see if she comes alive.

Thank you for the input guys! My biggest fear was maybe some computer malfunction. Hopefully it is just a bad connection somewhere. Its just strange because when it does have power, I know the connections are solid because she turns over fast and fires instantly. I've also used my thermal camera to look for hot spots at connection points, I didn't see anything alarming. Funny enough, she has had no power issues today. But I probably just jinxed myself...

Ill do some more testing this evening too see what I can find. Thanks again!

swathdiver · February 6, 2024

Pull that thing out the cigar lighter. Probably time to replace the cables going to the battery. Could be the battery itself, either a bad cell or an internal connection problem.

Any update on this?

Niklasbraun · February 6, 2024

You might wanna think about doing the big 3 upgrade sooner rather than later, especially if you're planning on slapping a 2000w inverter in there. It means upgrading the main power and ground cables, plus the alternator power cable.

Though your ohm tests for ground connections are cool, try using jump cables for a new ground path when testing during power loss. It could help catch any sneaky intermittent grounding issues that static tests might miss.

Since you're having trouble with the key turning, it's a good idea to check out the ignition switch and related parts. Look for loose connections or any signs of wear.

Also, you may do an electrical load test to ensure your battery's pumping out enough power. An on-and-off issue might be linked to the alternator or voltage regulator.

Jtcimp00 · July 23, 2025

Hey I know this is an old topic but did you ever find the solution? I'm having the same exact issues intermittently now and I am just starting to work on chasing it down.

BigBlockBurban454 · July 24, 2025

Howdy fellas, sorry its been a while. Things get crazy with work sometimes and we make the repairs, and head straight back to work while forgetting the people who helped us figure it out. Thats on me.

Simply put, this was indeed a bad battery connection issue. And you guys were right basically from the beginning.

After taking a day off work and testing wires and terminals for a solid 8-10 hours straight (about a year ago now), i finally found the intermediate break. The source ended up being the positive battery terminal, but not in the way you would expect. This truck has factory crimped battery terminals to the primary wires, with maybe 3 inches of sleeve crimped down (thats a lot and good). So i didn't even think to look at the battery terminal to wire connection itself.

I got desperate, as this is my work truck, after checking connections all over the truck. Fuse boxes, ignition cylinder, grounds, everything. So I cut the battery terminals off, and HELLO! A cloud of corrosion fell out of the positive battery terminal factory crimp connection, where the terminal is crimped to the positive wire.

I cut the connector open, as is standard in my line of work. If something fails, you have to do failure analysis. And sure enough, the wire and connector were completely corroded out inside, beyond view, with no obvious evidence before i cut it open. Sorry I dont have photos, I was trying to get the truck back on the road lol.

Replaced the connector and to this day, over a year later, not a single electrical hiccup with this truck.

Yall were right, bad battery connection. So kudos to the fine gents of the forum because its the last thing i was thinking. As a state licensed electrician, bad battery connection?? No way, ive checked it over and over. Boy was I wrong. Im just happy shes running like a top now.

Thanks again to everyone who put in the knowledge and two cents into this. If not for that, I probably would have never cut those battery terminals off and found the issue.