They have no clue or are guessing or throwing darts....all of the above lol. If bcm is offline that should have some sort of indicator as to being so. Check the data lines to make certain you have activity's. Check grounds and power to and from bcm.

 

Any specific questions your could give me to ask the mechanic? Or to ask other mechanics?
I got in touch with the GMC dealership to see what they would say. Biggest take away was that if it is the BCM they won't do the work, as the part if obsolete and they will not install 3rd party.

 

You glossed right over and ignored my question about the OEM Battery Terminals. Are they still OEM? IMPORTANT! If they are, they need to be changed. The FIRST mod to be done to every H3/H3T.

If your battery connections is inconsistent, then your BCM will not see sufficient voltage to properly communicate and needs a reboot (ie. correct connection to the battery).

Battery Terminals are inexpensive and easy to swap, easy stuff first.

If that is not it, then your BCM may be shorted or the harness may be compromised. Visual inspection is how to rule that out.

 

Oh, and going to the "dealership" would be an absolute waste of time on a 20 year old vehicle. They sell parts, not repairs.

 

i dont know if an H3 has a splice pack 205 like the H2 but i would start there. it ties all the networks together and maybe has some corrosion.

 

Key Symptoms of a BCM-Related No-Start:

• No-Crank/No-Start: The engine does not turn over at all, often with no sound, even if the battery is charged.
• Security Light On: The anti-theft or security light stays illuminated or flashes while trying to start.
• Erratic Electrical Behavior: Issues are accompanied by flickering lights, non-functional windows/locks, or random dash warnings.

 

NO>>>U0140<<<CODE?

 

Apologies for the late reply, but my own H3 has been keeping me pretty busy.

Here's what I would do:

1. Battery Terminals - Doc already said it; replace the crappy OEM ones with an aftermarket brand if they haven't been replaced already.

2. Disconnect the Battery First then disconnect all three wiring harness connectors from the BCM, as well as the antenna for the Lock/Unlock/TPMS. Two of the wiring harnesses are attached directly to the BCM, and one is separate from the BCM. Physically remove the BCM from the vehicle by popping out the two grommet/fitting/things (red arrows in my photo, you have to pop out the small tip on the grommet first, then the larger circular piece will come out easier), then open the black plastic housing enclosure that the BCM sits in. Spray all of the wiring harnesses, the Antenna connections, and the BCM Microchip itself (both sides) with CRC Electronics Cleaner (do not use a similar product, use CRC). Apply some di-electric grease to the antenna connection.

Here is a video that shows how to remove the BCM (skip to about 2:10).
3. Re-connect everything, and see if that fixes your problem. If it does great, if it doesn't, post back here and we can help you out further.

4. To prevent this problem from happening again, definitely do the sunroof modification to the grommets to help with the flow of drain water. It's not hard at all, but having small hands definitely helps. Here is a great video by H3 Humper on how to do this.

Courtesy of NMH3 from a different post. The three big circles are the three BCM connectors. The small circle is the TPMS/Lock/Unlock antenna. The arrows point to the grommets that hold the BCM in place.

Don't underestimate the power of simply cleaning all the electronic connectors, as well as the BCM itself; doing everything I did above was able to bring back my lock/unlock function on my wife's car (which does have a sunroof).

 

Spanovich008 - This is a great walk through. Thank you. Will move forward with this.
Question, you mentioned "lock/unlock function" - were you having an issue with the key fob / door locks?
Do you think cleaning my connectors and the BCM itself could solve my issue? I only ask because I can't definitively say exactly what my issue is, other than a generalized BCM issue. Regardless, I am sure this is a good first step to try and solve my issues.

 

No problem at all; hope it helps.

My wife’s Alpha was having trouble with the key fobs not working, and it was due to some corrosion/etc. on the BCM and its connectors. Simply disconnecting everything, spraying with CRC, applying dielectric grease to the antenna connector, and reconnecting everything was able to bring the key fob functionality back to life.

I’m not certain that this will “definitely” fix your problem, but I certainly don’t think it could hurt either.

Open up the BCM plastic housing and take a look at the microchip; you might be surprised with the amount of dirt/corrosion that is on there, especially if the sunroof mod hasn’t been performed.