Haunted Electrical System on GMC Sierra

Maintenance/Repairs
1

I love my truck, I really do, even though it’s haunted by poltergeists or possibly inhabited by gremlins. It started behaving strangely about a month ago, and despite the tireless efforts of my trusted mechanics, the cause remains a mystery. After days of diagnostic work, the service manager could come up with only one possible cure – an exorcism.

She’s a 2008 GMC Sierra 1500 SLE crew cab 4X4 with a 5.3 liter Vortec and about 78,000 miles. I bought her two years ago when she had barely 60,000 miles, and never experienced even a hiccup until recently. It started in the parking lot of Lowes on a fairly warm day. I jumped in, turned the key, and absolutely nothing happened. Dead, dead, dead. No dome light, no chimes, no buzzing solenoid. It seemed strange since I had replaced the battery about one year ago. I opened the hood, shook the battery, wiggled some wires, and tried again. Presto, it started right up with no further problems. I didn’t think too much about it for a week or so until the same thing happened again, but this time, it stayed dead. I had it towed to the aforementioned trusted mechanics, who said the problem was a loose battery cable, and it was returned to me good as new.

A couple of days later, I was leaving another parking lot after starting up, and heard a strange, rhythmic sound all around me. Not recognizing it, I looked around and discovered that all four of the door locks were popping up and down. At the same time, all of the gauges were gyrating back and forth, the seat belt chime was going off, the Check Engine light was going on and off, the status lights were flashing a wide variety of warnings and information, and the engine was doing a low-speed lurch. This possession lasted a minute or so, then all returned to normal.

Back to the trusted mechanics it went. They did their diagnostic magic and determined that there was a bad diode in the alternator, so it was replaced with a new OEM unit. Everything was fine for a few days, then the same weird stuff happened as I was coming down a mountain pass at 60 mph. This episode lasted about twenty minutes until I pulled over and parked. After the engine cooled, it started right back up and behaved perfectly. This time the trusted mechanics kept it for three days and did everything they could think of, including talking with the local GM service department to see if they recognized the symptoms or if there any active recalls. Zip, nada. In the end, they said they couldn’t reproduce the events and that all systems scoped out perfectly. They are at a loss.

I’m thinking it could be the battery – maybe an internal fault or defect? It’s a maintenance free type. All the posts, lugs, cables and connections seemed OK, but my non-mechanic thinking keeps coming back to the battery. Have you guys heard of this kind of eccentric behavior before, or have any suggestions on where to go next? Any advice would be much appreciated.

2

Sounds like maybe an intermittent bad ground connection. The following quote is from the link below.

"I have an “08 GMC Sierra 3500 and my ghost turned out to be a loose ground on the frame under the driver’s seat. There are several grounds attached to the frame. If your truck spends any time in the cold climate, I am sure that you have noticed rust on the frame. GM’s solution for corrosion control was to have the frames dipped in some sort of wax instead of painting them like the rest of the world. As soon as a single drop of water gets behind this wax it is all over and the wax starts to literally peel off. When GM installed the grounds to the frame they never cleaned the connection point off and the grounds were screwed on top of the wax. This works for a little while but once water gets behind that little 10mm bolt and freezes a couple of times, the wax and the bolt are loosened and the grounding point is compromised. You would think that they would have a service bulletin on this by now. You would also think that GM would have gotten away from those waxed frames by I just took a look at a 2012 and yep, wax frame that was already rusting. Reminds me of the early 70’s. Check all of your ground points. Loose grounds drive the ECM’s bonkers.”

3

Sloppy Joe Your non mechanic thinking could be 100% correct at least for the dead condition. The same thing happened to my 2002 Mitsubishi Eclipse. It had started normally and I drove it over the river and through the woods for a bit more than 8 miles. It was December and dark so I had lights and heater/fan going. Everything was completely normal. When I reached my little town I parked on the side street and went in the corner grocery for a few minutes. I hopped in the car turned the key and was greeted with nothing. I checked battery cables and they were tight. I just walked about 1.5 miles home , called my boss and told him why I would not be coming to work the next morning. In the morning I walked back to the car and tried. Same thing (or rather nothing). There was a convenient independent shop less than a block away. I walked over and explained my problem to the owner. He grabbed his jumper pack and we walked back to the car. He checked the cables which were fine. He hooked up the jumper pack and the car started normally. He drove to the shop just in case he could see, hear, or feel something. Once inside he turned it off and tried a restart. Nothing. His shop was clean and well equipped. He grabbed his multi-meter and probed the battery terminals. Zero continuity. We had drove to the shop on alternator only! Although I knew what this meant I politely let him explain. He asked if the car had been in a recent accident. I replied it had been rear ended a few Months after purchasing new but had been properly repaired. That was over 4 years past. He said that for some reason the battery had an internal disconnection which was very rare. He had a better than OEM battery in stock and after replacement the car started and ran fine. He still checked charging system, grounds, fuses, and codes! Some shops would say “battery bad” replace it and send you on your way. The new battery was $60 and labor was $40. More than fair! I gave the car to my Son in 2010 and it is still starting and running great. I would also take jesmed1’s advice. He has a similar truck and is talking from experience which could very well explain the “haunting”. I was hoping it would be a poltergeist or gremlins. That would be so cool!

4

Just to be clear, the quote I posted above is from someone else who owns an '08 Sierra with electrical gremlins and posted about it on the Edmunds site. I myself do not own the truck.

5

classic symptom of a charging problem.

When the system is not charging and the battery is drained almost dead…one thing that can happen is the locks go crazy.
Yopu already changed out the alternator so I say that either the battry cannot hold any charge, or you have a bad cable that is coroded so bad that the flow of electricity from the alternator to the battery is disrupted.

The same thing happened to my wife and as she was calling me to report the strange happenings…the car died.

I’d opt for a new battery

Yosemite

6

I opened the hood, shook the battery, wiggled some wires, and tried again. Presto, it started right up

How can you shake your battery? Is it actually just sitting in the tray unrestrained? Vibration kills batteries and stresses connections not to mention what could happen to an unrestrained battery in even a minor accident. Hopefully yours is bolted in properly.

7

jesmed1 OK. I now understand it is an Edmunds quote. I quess it still applies.

8

I’ve seen two things cause this type of behavior;

  1. a bad battery terminal post,
  2. a blown fusible link. The link looks like a wire, it runs from the positive battery terminal to an underhood relay box, and its insulation can hold the melted link together inside well enough to cause it to be intermittent.

TT, I can shake my battery enough to disclose an intermittent problem… and I’m just a weak old man! A battery does not need to be socked down tight enough to stay solid in place under heavy shaking. And many aren’t.

9

NONE of my batteries can be budged in the slightest when the OEM clamping mechanisms are properly secured.

10

Sloppy Joe, Did you ever figure out the problem? My 2008 GMC Sierra is doing the same things word for word. I have already replaced the battery and checked terminal connections.

11

Do you have alot of keys on your ring? My first thought is ignition switch.