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There is likely KAM (keep alive memory) in our BCMs, and people rarely use battery tenders with these trucks, so your low mileage means it probably sat with a dead battery more than once, and the KAM module in the BCM died, which stores everything required to operate everything except the core motor functions. I rarely drive (2010 with 61k), so we think sitting destroyed my BCM, and which in turn caused voltage drop issues, destroying the ECM.
Also be sure you are getting new BCMs that are fully functional. We found that most had dead or dying KAM modules from sitting in GM’s warehouse for too long.
GM uses flash based memory (Motorola PowerPC based 40 MHz, 32-bit RISC processor and a flash memory for 2006/7), like a thumb drive, juice or no juice, it doesn't matter, it can be stored near indefinitely. However, just like any flash based memory device, it could become corrupted by several things.... like voltage irregularities, surges, water/moisture intrusion, physical damage.....
What the OP described is typical of a wet BCM and/or short within the harness to the BCM. They won't fix themselves, but if it was wet, and now is dry, the short may no longer be present.
What the OP described is typical of a wet BCM and/or short within the harness to the BCM. They won't fix themselves, but if it was wet, and now is dry, the short may no longer be present.
Does this vehicle have a history of water getting in around the BCM if the car does not have a sunroof? Should I be looking for a leak somewhere as well? I know it was not raining the day the car went all haywire on me.
H3's are sensitive to voltage. Since the BCM was supposedly replaced, I would check for voltage drops. Start at the battery terminals and head to the fuse box. I have heard of fuse boxes corroding causing issues. Good luck.
I replaced the battery terminals today. While I was at it I hooked up a voltage meter and read battery voltage while running right from the battery, then along the fuse block. My lowest reading was 14.2 VDC and the highest was 14.3 VDC. So, holding steady. My next venture is going to be tracing out the grounds to all of the computers and making sure they have good connectivity.
The battery terminals went in without issue. I then hooked up a battery charger and just left it on for a few days to get the battery topped off. When I shut it off I checked the resting battery voltage with a meter and wrote it down. I'll go back this weekend and check it againto see if the voltage dropped any from just sitting; could be time to buy a new battery.
To get to the grounds I had to pull the front seats and the center console. The main ground for the BCM was under the carpet for at the rear of the console area so I peeled the carpet up from the front back. Fun fun fun.
I have decided to re-run the power circuit to the BCM. If power fluctuations cause issue then I will eliminate that by running new hot and ground wires. The only plugs I will have to deal with will be the ones into the BCM itself. I'll snap a few pictures once I am finished.
The main fuse block ground is just behind the battery box (between the battery box and fire wall) and is a black wire running to a stud on top of the metal inner fender. That can get real cruddy, give it a look.
The main fuse block ground is just behind the battery box (between the battery box and fire wall) and is a black wire running to a stud on top of the metal inner fender. That can get real cruddy, give it a look.
Funny thing was, that was the easiest one to get to. It had 4-6 terminals under the screw. I gave it a bit of a loosen then tightened it. There was no corrosion. Under the carpet looked good as well. Everything looking good is what led me to just running a new hot and ground from the BCM back to the battery. I will just put in an inline fuse.
The main power to the BCM comes in on A7 (orange wire), so I'll just cut it off at the BCM and run a new one straight from the battery. The same with the ground.
Your rig has low miles. In the past I have found vehicles with low mileage having, rodent intrusion, chewing wires, causing shorts and abnormalities that you described above. Visual check. Here's a great article on what to look for: https://axleaddict.com/auto-repair/C...ice-Ruin-A-Car
I checked all the harnesses for evidence of rodents; I have been lucky and there isn't any chewing or left over nests.
I completed running new power to the BCM. I used a #14 shielded cable with 2 conductors and soldered the wires on the BCM side then covered them with heat shrink. I applied dielectric grease to all the plugs I could find. While I had everything taken apart I mounted a dual USB outlet on the back of the center console and replaced the shifter boot. I'll keep you all updated on how everything works out.
Almost 2 months since my last update on this thread. I have had zero issues with the car since the last round of repairs. I have a cigarette lighter plug in voltage meter to keep an eye on the battery voltage and it maintains 13.5-14.2 VDC while running. I do appreciate all the help along the way.
03-15-2019, 09:38 AM
