I suspect BCM... thoughts?

[Joseph Garcia]

Actually, Joseph, new BCM’s for the NNBS are closer to $200. Search GM 25835966, the correct one for the OP’s truck. I noticed this because I’ve replaced mine in my 08 Silverado and remember it wasn’t cheap. I ended up buying a used one.

You are absolutely right, Mark. I stand corrected.

I just re-looked at my BCM replacement invoice, and it was $172.

 

[intheburbs]

What I don't understand is that when the problem(s) occur, a quick disconnect and reconnect of the battery and everything is set right again. That's what was making me think computer related - like it was being reset.

The loose connection causes a voltage drop, throwing the electronics into disarray. You're right, doing a disconnect/reconnect reboots everything and gets it back to normal.

But the problem is wiring, not the computer(s).

 

[Doubeleive]

I find it highly unlikely that any intermittent problem is computer-related. They either work, or they don't.

This is completely and utterly a bad electrical connection issue. I'd even replace both battery cables. Check the primary feeds to the alternator, to the mega fuse holder, and to the load center. You checked grounds? Check them again.

And yes, those wires in the footwell were for a brake controller.

you are partially correct, however heat can cause problems with electronics. A electronic/computer can sometimes work perfectly fine until it gets hot, a component expands and looses connection. not saying this is the OP's issue but it can be a problem.

OP what you can try also is get a cheapy code reader if you don't want to spend the bucks for a tech2
when the no start issue happens, instead of disconnecting the battery try clearing the bcm codes even if it doesn't show any, doing this reset's the bcm
if it works and starts that may be a clue doesn't mean it's the bcm as it could be anything attached to it, but it's a clue that may lead to the root cause with a deeper diagnostic.

 

[Just Fishing]

New ground for battery to passenger head and to frame coming today. Other main ground was braided cable from rear drivers head to firewall, and also checked one under driver's footwell at the frame. My truck is pretty corrosion free and the connections are tight.
While I'm in there I'll take them off and sand/wirebrush the connection points as a double-check.

What I don't understand is that when the problem(s) occur, a quick disconnect and reconnect of the battery and everything is set right again. That's what was making me think computer related - like it was being reset.

Look down under the driver side.
there are several ground locations on the subframe.
one right under the driver seat, and another under the second row.
IIRC there is a third in there as well.

The one that was really bad was under the driver seat (If I Remember Correctly).

it was a large spade connector with a few wires going into the location.
I had to cut the shrink tubing off to see how nasty it was.
otherwise, it looked perfect.

If you don't want to cut and redo the connector,
a little rosin or flux with a little heat will flush the connector out.
then flow in some solder.

I noticed I didn't have very much wire length, so I decided to just clean and flow solder into the current connectors.


To re-seal,
I got creative.


The easy way would be to just use some liquid electrical tape.

but since I didn't have any of that on hand, I used some marine grade shrink tubing (built in glue)...
but since the connector is already installed, I used a light coating of black rtv (since I always have it on hand).
then took some of that shrink tubing that fit the wire nicely, cut it into nice tight spirals, spun it on the wire and then did it once more to ensure the loops crossed with slightly looser spirals.
Applied some heat to seal it up, after the rtv had a chance to thicken up, and finished with another coating of RTV.

 

[TrybalRage]

OP what you can try also is get a cheapy code reader if you don't want to spend the bucks for a tech2
when the no start issue happens, instead of disconnecting the battery try clearing the bcm codes even if it doesn't show any, doing this reset's the bcm
if it works and starts that may be a clue doesn't mean it's the bcm as it could be anything attached to it, but it's a clue that may lead to the root cause with a deeper diagnostic.

I have a super cheap bluetooth dongle that I use with an app - not the type that can read BCM codes, just basic engine codes and clear them, view ready status, etc.

When the truck starts acting up, it cannot connect so won't give me a reading of anything.

I'm afraid if I had one that could read BCM codes it might have the same problem.

 

[TrybalRage]

I got the new cable today but didn't get it installed yet. I also ran out and got another generic negative cable to add an additional ground (one of my searches here led to a video that showed that, and you can never over-ground, I suppose).

I also found this document: https://www.autocodes.com/uploads/gmc/08-07-30-021E.pdf So after I get the new grounds installed, and clean up the other existing connections, I'll take a look at the transmission connector as well to see if anything looks awry.

 

[petethepug]

If you need a code reader / clearing tool that stays the in the truck 24/7 and invisible there’s this option for under $2h.

There’s more that accompanies this but it allows you access to every code generated on the fly.

2007-2014 AutoSync-G2 (GMT-900)

IMPORTANT NOTE EFFECTIVE JANUARY 15th 2023. All AutoSync's now include the torque converter lockup controller feature as standard equipment, however it will only be active/function on 6.6 Duramax diesel vehicles. The new second-generation AutoSync-G2 is now available...new features and...

www.btdieselworks.com

 

[Doubeleive]

I have a super cheap bluetooth dongle that I use with an app - not the type that can read BCM codes, just basic engine codes and clear them, view ready status, etc.

When the truck starts acting up, it cannot connect so won't give me a reading of anything.

I'm afraid if I had one that could read BCM codes it might have the same problem.

that's pretty odd, well whenever you get it resolved be sure to post up what it was
sometimes replacing the ground cable seems to fix things for a short period then the problem comes back so be sure to give it a few days

 

[chevylade]

I find it highly unlikely that any intermittent problem is computer-related. They either work, or they don't.

A bad BCM can cause very random and intermittent problems though my experience with a bad BCM didn’t cause any of the symptoms that the OP described. I’ve used Highway 71 for a programmed BCM and was satisfied with what they sent me. I agree that it seems like a connection problem.

 

[TrybalRage]

Well added the new negative cable today, sanded and wire brushed the connections at the lower front passenger frame, firewall on the driver's side, and ground under the driver's footwell. Added a new 4GA cable from the driver's head to the same point as the braided line on the firewall.
Reinstalled the BCM, heat shrunk the ends of the auxiliary trailer brake wires and zip tied them out of the way.
Truck fired and runs fine, so I guess now we wait. I parked it outside in the sun to simulate the conditions of last week, so we'll see what happens.

 

[Rocket Man]

Well added the new negative cable today, sanded and wire brushed the connections at the lower front passenger frame, firewall on the driver's side, and ground under the driver's footwell. Added a new 4GA cable from the driver's head to the same point as the braided line on the firewall.
Reinstalled the BCM, heat shrunk the ends of the auxiliary trailer brake wires and zip tied them out of the way.
Truck fired and runs fine, so I guess now we wait. I parked it outside in the sun to simulate the conditions of last week, so we'll see what happens.

 

[TrybalRage]

Well, no bueno. Started up all afternoon yesterday fine sitting in the sun. Went out this afternoon, no start.

What I'm dealing with - note the no indicator of the shift position. That's always a dead giveaway it won't start.

Battery voltage showed 12.2. Little low considering I just charged it on Sunday. Removed positive cable (it's easier to get to on these stupid things), waited 5 seconds, reattached it, fired right up.

 

[Rocket Man]

Well, no bueno. Started up all afternoon yesterday fine sitting in the sun. Went out this afternoon, no start.

What I'm dealing with - note the no indicator of the shift position. That's always a dead giveaway it won't start.

Battery voltage showed 12.2. Little low considering I just charged it on Sunday. Removed positive cable (it's easier to get to on these stupid things), waited 5 seconds, reattached it, fired right up.

Have you removed the positive battery cable and mega fuse and inspected for internal corrosion/ dirty terminals? Or removed the under hood fuse panel and looked for corrosion underneath where it plugs in?

 

[donjetman]

Battery voltage showed 12.2. Little low considering I just charged it on Sunday.

12.2v is half dead
40% to 50% SOC-state of charge

 

[TrybalRage]

Have you removed the positive battery cable and mega fuse and inspected for internal corrosion/ dirty terminals? Or removed the under hood fuse panel and looked for corrosion underneath where it plugs in?

A the battery everything looks clean as a whistle. No corrosion, no buildup of any kind. I have not inspected the other end at the fuse box.

 

[TrybalRage]

12.2v is half dead
40% to 50% SOC-state of charge

Right, which originally had me chasing a parasitic draw for the past 6 months. But when I test across all the fuses like this video shows, all show 0.

And if it was just low voltage, why does it immediately start after a quick disconnect/reconnect? Makes no sense to me.

EDIT: I tested across all the inside and inside fuses that I could, EXCLUDING the J-case fuses cause I couldn't figure out how to do so since the caps don't allow access the same way.

 

[Rocket Man]

A the battery everything looks clean as a whistle. No corrosion, no buildup of any kind. I have not inspected the other end at the fuse box.

The fuse box will detach with the 2 big latches and pull straight up, you’ll be able to see underneath where everything plugs in. Disconnect the battery first. There’s been plenty of people who have found corrosion in those connections. The mega fuse is on the firewall, that’s where the positive cable goes to.

 

[TrybalRage]

The fuse box will detach with the 2 big latches and pull straight up, you’ll be able to see underneath where everything plugs in. Disconnect the battery first. There’s been plenty of people who have found corrosion in those connections. The mega fuse is on the firewall, that’s where the positive cable goes to.

I'll take a look then. The mega fuse on mine is right at the positive terminal, part of a bracket that includes the terminal connection.

 

[TrybalRage]

Ooh, we've got new info. I'm pulling U0101 and U0102 codes (lost communication with TCM and Transfer case). Well that would explain the dash errors.

Looks like I've got some deeper inspections to do. I found a longer/more detailed TSB document here: https://static.nhtsa.gov/odi/tsbs/2012/SB-10043829-6448.pdf

So the short version is, every single harness everywhere in the vehicle could have been rubbed through somewhere and everywhere all at once. Yay me.

Anybody want a 2500 suburban? Ugh.

 

[sunureu13]

Chiming in on this thread since I'm having the same issue on my 2007 Escalade. Normally the threads I find from google are a decade old so it's nice to see a current one.

I had exactly the same issues; no crank no start with the missing prndl indicator, various other circuits not working like exterior and interior lights, radio, tailgate, etc. Never had low battery voltage with those symptoms.
Like you, disconnecting the battery fixed everything but sometimes it would take a dozen or more tries to "reset" it. I could never figure out the cause.
At first I suspected a ground issue but I had gone through all my grounds, plus the fact that since I have a high powered audio system (5000W RMS+) all my grounds are absolutely solid. 4/0 OFC under the hood and dual 1/0 OFC to my rear lithium battery. Amplifiers grounded with the same. I had removed the factory battery ground since I no longer had an underhood battery. In addition to the factory grounds, I had added block to frame, block to body, and body to frame under the hood and had battery to frame and battery to body in the rear.
Then I found some info on the junction block (underhood fuse block) having issues with corrosion or bad board traces or something. My coworker had the same issue with his Tahoe. I removed it, checked for any loose terminals, cleaned it up and reseated it. That managed to fix my issue again for a bit, but I still had to disconnect the battery a few times to fix it again.

Last week, I had an occurrence of the issue that likely completely killed several cells of my lithium bank (dropped me all the way down to less than 6V on a 13.8V bank), or several of my cells died all at once and caused the issue too occur(?). Replaced it with an AGM and no amount of fiddling with the ground cable or junction block fixed it. So I replaced both the junction block and the base since some of the tangs that hold the harness connectors were broken. Still have the same issue.

Today, I went out with my tech 2 + CANdi module and checked what I could (battery was at 11.8V from messing with everything so much so I'm waiting for it to charge in a few hours). Turns out I had connection with the TCM, liftgate, radio, ecm, and all the stuff I thought wasn't working for whatever reason. The only thing I couldn't connect with was the BCM. BCM controls a bunch of the stuff that isn't working and also I think the transfer case module and some other things related to actually starting the truck. I still have to find the wiring diagrams. I'll be going back out in a few hours to investigate.

So your issue still may be grounds, so definitely disconnect everything, sand down to shiny metal, apply dielectric grease for protection, and also check the resistance of the wire to see if there's any internal corrosion. I'm not an electrician but my grounds were in the 0.1 to 2 ohm range, including through the frame from back to front. I think I read somewhere that less than 5 ohms is acceptable, but someone should correct me if I'm wrong.
Or your issue could still be BCM, since GM was very bad with soldering (just ask anyone with a 98-00 Corvette that had ABS issues) and that would make sense why you have the issue more often in direct sun rather than in the garage.
But definitely check all your grounds first and I hope you have some good news when you reply. I hope I have some too.