Dead battery...2020 L5P

[Tomato]

My truck threw 2 codes last week - P0700 and U0100.  I searched around and found this post and attached TSB. The TSB fixed my issue, and it could very well be what is causing the dead batteries.  The bolts on mine were only at about 12 inch-pounds.  Tightened them up to 53 and all is good!  I am also wondering of this will fix my trailering app gremlins - have not towed yet.

 

 

Fuse Box TSB.pdf

[KC Desert]

On 5/31/2020 at 6:00 PM, Revspan said:

Drove my truck last week, and went to move it today and the battery was completely dead.  Good that it was in my garage and not locked.  
 

anyone hear of some kind of parasitic drain issue?  
 

truck has 2k miles on it...absolutely no mods.  
 

thanks

Holy cow dude mine just did this tonight! Deader than a doornail. My trickle charger can’t even resurrect it. WTF GMC.  It had updates a month or two ago. I’ve owned it since last September. Nothing is plugged in and no mods.

[KC Desert]

5 hours ago, RossEGCA said:

I had the same issue with my 2020 Sierra AT4 HD.  I jumped it the first time and it was fine.  Second time I charged overnight and it was fine.  I took it to the dealer as it threw some check engine codes due to low voltage.  they cleared the codes and tested the battery and said it was fine.  I said then why does it keep dying?  They don't know.  So far its been 4 weeks and no other problems. Strange thing is with two batteries there were no warning signs like slow start, etc.  Just went from fine to dead overnight. 

Exact same issue here. 

[Maryland]

To clarify, it actually happened three times now, and battery is NOT actually low when checked, and throwing NO codes per dealer.

It just won't crank/start.  No sound no grinding nothing.... just won't start.

Only power is horn and headlights.

 

After unhooking both batteries for a period of time, and reattaching it has started.  (Not sure of course if this action had anything to do with it starting, or if something just restarts after a certain amount of time.

 

How do you get the truck out of park when this happens.  Can't even do this when its down

[Tomato]

Have you checked the fuse box???  Per my post a few up from here.

[KC Desert]

I tried to jump it off, nothing. Just called for roadside assistance at my house LOL. The truck is parked on the driveway right up against the garage with the electronic e-brake ON. No way to move it if it has to be towed. 

 

I also checked the fuse box torque and they are all good. 

 

Roadside assistance jumped it off then it died again after a few seconds then the windshield wipers started running for no reason and it would not take any further attempts to jump. Parking brake is still set. UGH. GMC.

Edited August 19, 2020 by KC Desert

[KC Desert]

Got it jump started but the emergency electronic brake won’t release and OnStar was zero help and the dealer had no idea. Is there a fuse I can pull? 

[Tomato]

24 minutes ago, KC Desert said:

Got it jump started but the emergency electronic brake won’t release and OnStar was zero help and the dealer had no idea. Is there a fuse I can pull? 

If it has power, do not hold the brake and hold the start button for 10+seconds. You will go into maintenance mode. Try releasing the park brake from there.

[KC Desert]

44 minutes ago, Tomato said:

If it has power, do not hold the brake and hold the start button for 10+seconds. You will go into maintenance mode. Try releasing the park brake from there.

That worked thanks! It has all kind of engine lights on now but was able to drop it at the dealership. 

[Tomato]

33 minutes ago, KC Desert said:

That worked thanks! It has all kind of engine lights on now but was able to drop it at the dealership. 

Glad to hear it.  I figured that out when I wondered how to get the truck out of park without it running...

[KC Desert]

20 minutes ago, Tomato said:

Glad to hear it.  I figured that out when I wondered how to get the truck out of park without it running...

OnStar was useless, they had no clue. This worries me that our all electronic rides can be completely disabled like this.

[kylant]

1 hour ago, KC Desert said:

That worked thanks! It has all kind of engine lights on now but was able to drop it at the dealership. 

i see you are in Nevada. What dealership may I ask?

[KC Desert]

26 minutes ago, kylant said:

i see you are in Nevada. What dealership may I ask?

Findlay has it, they have done well before. They are telling me it is a module that has to be replaced and they will just charge my batteries, no replacement even though they were completely dead. I would think that would be a replacement item. 

[KC Desert]

On 7/9/2020 at 6:53 PM, dudleyfj40 said:

Hey guys, Just got my 1500 6.2 with 700 miles on it back from the shop for the same dead battery issue. From what the dealership told me, that brake modulator stayed on when It was shut off. I guess there is a Bulletin on this issue. They claimed to reprogram the modulator and all should be fine now. 

 

The dealer just called me and said it was a Glow Plug modulator. How many modulators does this thing have stealing power from the batteries?

[WoodworthFencing]

I have the same issue with my 2020 AT4 HD. I pull a trailer everyday, so there is a chance that it may be something with the trailering modules. I also have the screen on the stereo go black before it dies. I have had it die about 4 times in 6 months. They did the update at GM to the BCM and I woke up to it dead once again. I am about ready to light a match. This is the 3rd time that it was dead on a Monday morning. The battery was at 2.9 volts, which is obviously super low. Something is going on when it is supposed to be off. I have also noticed that when I am hooked up to a trailer and the truck is off, that the lights on the trailer will flash quickly one time about every 60 seconds or so. That is kind of weird.