Random complete loss of all electrical power overnight

[Stevalli]

Hi everyone! I am new here, but I am finally tired of putting off getting my Tahoe fixed. It’s a 2003 5.3, and for the past year and a half has been giving me the strangest electrical problem. Basically, it started when the truck sat for about a month because my window got smashed and I just didn’t drive it. Once I fixed it, I charged the battery up and everything seemed fine for a few days. I drove it every day, and then one morning I go out to start it and there is nothing. No starter, no dome lights, no dash power… nothing. I wasn’t sure if something was left on, so I charged the battery later that day and put it back in. Again, completely fine and normal for a few days and then one morning nothing. I eventually replaced the battery because it had been a few years old, and the same conditions happened to the new battery too. The alternator is a few years old with probably only 20k on it (oem).
Fast forward to today and I’ve pretty much let the truck just sit. I was stumped and my motorcycle and other cars are here for me to drive, so I put off fixing it. But I went out yesterday and bought a multimeter to try and start figuring this all out. When put in ground line between battery and cable, the multimeter initially reads a little over one amp, but falls in big jumps and eventually reads 0 draw. Again, the drain was completely random and it was big enough to suck all the life out of the battery, so I have no clue how to go about addressing it. Any help would be greatly appreciated… thank you all!!

 

[OR VietVet]

Welcome to the forum from Oregon.

Do you have an alarm system on vehicle?

If can get the draw that big to stay on and start pulling fuses, you can diagnose that circuit. Are the ends of cables completely clean and free of corrosion and no corrosion down the cable in the insulation?

 

[Stevalli]

That’s really where I’m stumped… I have no clue what is triggering this random depletion, so it’s hard to know when it will happen or when I’d be able to measure it on my multimeter. I did pull off the terminal connection covers and clean them off on my last go around with this, and that didn’t seem to help. Maybe it’s an issue further down the power cables? Id like to know for sure before I go start replacing things since funds are a bit tight haha

 

[Stevalli]

As far as alarms go, it’s only what the car came with from factory. Aside from speakers, there isn’t a single non-oem part in the truck

 

[OR VietVet]

That over 1 amp draw is too much. Rule of thumb, years back, was 50 milliamps or lower and now I think is more. If you start by checking it each day and get the initial 1 amp draw that goes down, then you have a pattern. Then start by unplugging the alternator and see if that 1 amp draw is still there the next morning. If is gone and then plug back in and it comes back, well there you go. You can also unplug other components and see if that effects it and it will take a while but can narrow down the problem.

The cables will not cause the draw, unless they are crossed somewhere down the line, but can cause a loss of voltage needed to turn the engine over.

 

[Stevalli]

From what I understood, the initial spike is normal when you close the circuit with the multimeter and all the systems cycle. It only reads that high for about 10-15 seconds, after which it drops to essentially zero (every now and then it will flash .01). From that it would seem like everything is normal, which aligns with the fact that the car only randomly loses power.
Maybe this truck of mine came to life and is playing pranks on me idk, but even if there is something that intermittently draws power every few days, it’s hard for me to figure out what could pull so much power that there is nothing left at all.

Again, my knowledge on electrical is very elementary, so if this could be the result of some sort of grounding, shorting, or some other issue, I would need some guidance lmao

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[Fless]

Can you show us a pic of the ammeter you're using, with the scale selected that was used when the ".01" value flashed on and off? Perhaps also show how the cables were connected (plugged in) to the meter?

 

[Stevalli]

Thank you to those who have replied so far. The multimeter was set to its 10a setting. I know that the multimeters fuse is good because it initially reads high when the computers systems cycle, but it falls to a very low number. I was worried to put it to the 200ma setting because of that initial spike being above 200ma, so I didn’t know if it would blow the multimeters fuse (but I did think of tying the system together with jumper cables to get past that initial spike, then attaching multimeter and disconnecting jumper cables. Not sure if this would work like it does in my head).
The past couple days I’ve been driving the truck around, paying close attention to check the batteries voltage at different times. I disconnected the battery last night, and it fell from 12.56 to 12.46 overnight, so now I know that this new battery I bought isn’t in the best shape anymore. I plan on leaving the battery connected tonight to see the effect it has.

 

[Stevalli]