I got a replacement BCM, flashed to my Vin, delivered today. It included info about PhasekeyIII and Key code. Is there more to this than just swapping the old busted with the new flashed one?

Disconnect the battery before swapping it.

1ags always coming through! Battery is already disconnected. Aside that, plug and play? Or do I need to do that other stuff as well?

Nope, if shes preflashed you should be good to go.

A scholar and a gentleman. Always helping me out.

I forgot if I posted this, but I used flaming enterprise for PDR, good dude and spoke highly of you

Hey 1 ags, I swapped the BCM without battery. After getting BCM plugged in and situated, I put the battery back on. I am still not able to get the vehicle to even to try to start and all the previous lights (stabilitrack, tire pressure, etc) are all still lit up, as it was with the previous BCM. Eventually I get dome lights and AC panel on, but when trying to start, the lights dim and healights go off, but no clicks or attempt to turn. The battery is new and has been on a trickle charger to be at 100% before this was attempted. Additionally, a new negative/ground cable was installed before this to rule that out.

Any guidance? Is there some key/programming issue?

What was the first reason for BCM replacement ?

Never had problems, especially of this nature. Drove from Timbergrove area to Katy. Parked and was off for about 20-30 min. I come out and nothing came on but got Stabilitrak light. I waited about 5 seconds, tried again. About on the 5th try, it cranked and was able to get home. I parked and it has been DOA ever since. I swapped battery, and negative/ground cable trying this first. From online searching, with all these lights on, no crank, etc, it seemed to be BCM.

When I put to the "accessory" position, after a few seconds, all the CEL (variations) lights come on, the AC blows low, no radio, no power locks/windows, the keyless entry does not work. Etc. I guess time to start chasing fuses?

Check the maxi fuse in the red plastic box.

Is that the one in a little box bolted up on the firewall by itself?

I checked the little mega fuse on the firewall with a multimeter, still reading ok. I checked the 40A starter under the hood (3rd diagram, #62). I also checked the Run/Crank (3rd diagram, Run/Crank).

https://www.autogenius.info/chevrolet-suburban-2008-fuse-box-diagram-2/

Should I start just go fuse by fuse? Or could it be that the mega fuse is still reading but is on its way out/not carrying enough power?

Did you bench test the battery and starter?

To answer your question(s): no. The battery is brand new, have not fooled with the starter.

A little other info, there are no current codes. This Tahoe is very much a garage queen with ~35k miles, has rarely seen inclement weather.

I cant' help but think this is electrical. The keyless entry is not working, the power doors and windows are not working, no radio. The overhead lights that would normally come on when the door is opened, do not. It takes a good bit after turning to accessories to get anything to come up on the cluster.

So far, its not: negative/ground cable, BCM, Mega Fuse, or 40 A start fuse.

sawemoffshort07 said:

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To answer your question(s): no. The battery is brand new, have not fooled with the starter.

A little other info, there are no current codes. This Tahoe is very much a garage queen with ~35k miles, has rarely seen inclement weather.

I cant' help but think this is electrical. The keyless entry is not working, the power doors and windows are not working, no radio. The overhead lights that would normally come on when the door is opened, do not. It takes a good bit after turning to accessories to get anything to come up on the cluster.

So far, its not: negative/ground cable, BCM, Mega Fuse, or 40 A start fuse.

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What are you using to pull codes? Can it actually communicate with the ECM? Most of the systems you listed are controlled by the BCM, but to me, it sounds like there's an issue on the gmlan network since you've replaced the BCM.

Starting circuit goes ignition switch > bcm > ecm > starter. If there's a databus issue, the BCM won't signal the ECM to run the starter relay. The radio is also on the gmlan, but it isn't directly controlled by the BCM.

There's a TSB covering troubleshooting canbus issues on this era GM

https://static.nhtsa.gov/odi/tsbs/2012/SB-10043829-6448.pdf

I'm using a Bluedriver. When I was verifying that, there was a code C0561. This code was before BCM replacement, as I figured it was erroneous reading due to whatever else was happening.

After reading over that bulletin, looks like I'm off for a data link resistor tomorrow

Found the connector, tucked away. Going to get replacement in ~30 min

sawemoffshort07 said:

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Found the connector, tucked away. Going to get replacement in ~30 min

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Did you check to see if it was chafed or shorted? I can't tell from the picture.

That TSB wasn't specific to the code you have. I suggested it more for tips on how to troubleshoot the canbus. I wouldn't parts canon this. Wiring issues can be a PITA to track down w/o a scan tool and time

I replaced the resistor and we are back to cooking. Thanks so much!

With the resistor fixing the issue, I thought I could pull out the new BCM to return. So I put back the original BCM and about a minute later, we were back to dead. So I guess the OEM BCM is shorted and is causing the resistor to short out and kill the vehicle. I swapped back to the "new" BCM and will have another resistor tomorrow. Should have left well enough alone, but thought I could get ~$190 back.