I suspect BCM... thoughts?

[TrybalRage]

I've owned my 2010 Suburban 2500 for maybe 9 months now. I've had intermittent no start (won't crank) issues that I've always related to the battery. The first time it happened, it was also throwing all kinds of errors - 4WD, stability, ABS, etc. The shift position wouldn't display correctly. The rear hatch was inoperable. None of the gauges displayed that I can recall.

Replaced the battery and all was well.

Since then, on occasion it wouldn't start. Turn the key, power on everything, go to crank, everything goes blank. It would never jump without first removing the negative battery terminal first (in retrospect, I believe this was resetting the computers).

I figured it was a parasitic draw somewhere so I got in the habit of keeping it on a battery tender. Figured I'd get around to fixing the issue one day. I don't drive it often so it wasn't at the front of my mind.

Well earlier this week, twice it left me sit after being parked out in the hot sun for 6 hours or so (I usually park in my garage). Both times I got jumped, including having to remove a battery cable first.

So yesterday I start trying to find a parasitic draw. I was using the current draw method across my fuses, and on all the fuses I could check I'm showing 0 millivolts of activity. (Also, I've been keeping it in my garage and it's been starting fine when I do try). Well I had to run out at my lunch break, so I fired it up and went out to the store. On the way home, I heard a slight pop from somewhere inside the dash and all of a sudden the same errors - service 4wd, abs, blah blah. All gauges go dead except for the voltmeter. I can't be sure but it felt like much reduced power. Luckily I wasn't far from home.

Pulled in the driveway and started fiddling with things, turning it off and on, and it would restart fine several times until it suddenly did the black-out no crank again. I grabbed my voltmeter and checked the battery - 12.7 volts. So I simply removed the cable and attached it again, and it started up - no more errors.

So now I'm thinking I don't even have a draw - or if I do it's not my primary issue. I suspect the BCM may be bad, and it is being especially affected by heat. Before I start chasing down this rabbit hole, does this sound plausible? I don't own a tech2 so it would probably just be off to the dealer, unfortunately.

 

[TrybalRage]

On a side note, this truck was previously a "commercially owned" vehicle - to whom exactly I have no idea. But off the same harness that plugs to the BCM I found a bunch of cut wires... any idea where these are supposed to go?

https://imgur.com/Q8eCRGu

 

[donjetman]

Aftermarket trailer brake controller???

 

[gpracer1]

Could be brake controller wiring, need to follow it or put a meter on it and see what does what if you hit the brakes, etc.

 

[TrybalRage]

It goes right into the under dash harness. Someone on FB suggested it was there from factory for people who wanted to run an aftermarket brake controller.

https://imgur.com/rVAQBuU

But I'm not sure this is causing my intermittent black-cluster no start condition.

 

[Rocket Man]

Possibly a bad ground or corrosion in the battery cables. Check to see if it looks like any of the cables have internal corrosion present where they attach to the terminals at each end. Also inspect at the **** fuse, remove everything and clean it up. Check any grounding points, there might be corrosion. Also sometimes the under hood fuse box gets corrosion underneath where it plugs in. You can tap on it with a mallet using a block of wood on top to see if any problems change for the better or worse or remove it and inspect underneath- it unclips and then you can lift it up. Electrical issues are a PIA.

 

[TrybalRage]

Possibly a bad ground or corrosion in the battery cables. Check to see if it looks like any of the cables have internal corrosion present where they attach to the terminals at each end. Also inspect at the **** fuse, remove everything and clean it up. Check any grounding points, there might be corrosion. Also sometimes the under hood fuse box gets corrosion underneath where it plugs in. You can tap on it with a mallet using a block of wood on top to see if any problems change for the better or worse or remove it and inspect underneath- it unclips and then you can lift it up. Electrical issues are a PIA.

Yeah I've been digging though other posts and it seems that grounds grounds grounds always comes up. I've already inspected all the main ones in the engine bay and they're in good shape and clean and tight. But I saw in one post that the factory negative cable was failing even though it looked fine on the outside.
For $50 or so I'll give that a shot first.

 

[swathdiver]

Tech-2 time.

 

[Fless]

The 4 wires you showed in post #2 do appear to be the OE wiring for an aftermarket brake controller. As long as they don't touch any other wires, it shouldn't cause any issues with anything else. The red wire is fused, and if you're not going to use a brake controller I'd advise to disconnect it from the side stud in the underhood fusebox. eTrailer has videos on installation and they show the stud locations.

 

[petethepug]

As a matter of required general maintenance the battery grounds should be replaced. They rot from the inside out effectively acting like a backed up pipe. Essentially it drains slower & slower until it’s time to call a plumber when it doesn’t.

The presumption of the BCM failing goes hand in hand with the grounding issues. The boards get cold joints. The price of replacement is so inexpensive that it doesn’t make sense not to swap out both when the signs are there.

$129 for a coded replacement BCM.

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