I will try to make the back story short. We are a Car audio shop contracted with electronics work for the US Forest Service. 2018 Chevy 1500 with battery drain. Tested battery/marginal - replaced. Draw test started at around 3.9A until vehicle went to sleep then rests at .024 which is fine but with meter on record overnight something was waking up to draw .44. I noticed the overhead seatbelt indicator never ever shuts off, traced the light staying on to Airbag Sensing and Diagnostic Module - GM (13522335) under center console. If i unplug the smaller of the 2 plugs light goes out but drain is still there, unplug the bigger of the 2 plugs and drain goes away. Feeling confident that part was the culprit I ordered a new one and had it VIN coded. Light remained out and vehicle was showing no codes nor drain at this point. I buttoned the vehicle up and proceeded to top off the battery, this is where I noticed something still wasn't right because the battery wouldn't fully charge. This time I connected my meter just to record voltage drop over time and from 3:09 and 12.43V to 4:53 to 12.15V. It is curious that with my meter set up in line with the negative battery wire I come up with an acceptable draw but when the negative cable is actually hooked up to the battery the drain starts. At this point I am thinking BCM but that is just a guess.
