NoHairRob

Apologies up front for the length of this post
First time poster, please be gentle.
2011 HHR base model
203729 miles
automatic
not sure of engine (no sticker in engine bay) edit vin check 2.2L

I was having a random U0073 code. While searching this forum came across the video to remove clean and reset the under hood fuse block, did that. Also removed the other wire connectors just in front of that fuse box and cleaned contacts and reset. Also did the BCM inside the car in the center console. Before reattaching the battery, cleaned all connections back there. Now after reattaching the battery, I have nothing that is controlled by the BCM working, no crank, no windows, no AC blower, no power seat, no wipers, no headlights, and I am sure I have missed something. Interior lights work, door locks work, key fob door locks work, radio works. Since this started, I have undone all that I did, unhooked battery, cleaned and removed all dielectric grease, on all wire connectors with a good electrical contact cleaner/ degreaser and reseated all connectors, I have pulled and verified all fuses with a meter and checked for 12 volts at all places I could think off with the battery connected to a battery charger, to make sure voltage stayed above 12.5. My scan tool now shows the ECM only while before it had communication to the TCM, EBCM, and SIR (airbag). I have also used the multimeter to check the OBD2 port, voltage good, and the resistance across pins 6 and 14 shows the the can bus is completing the loop with 60 ohms. I can not find a wiring diagram for the BCM plug inside the car to see if voltage is at the BCM. Any help will be greatly appreciated!!!!

donbrew

You can tell which engine by your VIN. https://driving-tests.org/vin-decode...20model%20year.
My first guess is that one or more of the pins in a connector got bent or pushed out the back.
When you reassembled the under hood fuse box did you tighten the bolts until you heard clicks? They need to be a lot tighter than you think.
You do have some things controlled by the BCM. " Interior lights work, door locks work, key fob door locks work, radio works" That probably means one of the "BCM" fuses in the underhood fuse box is not connected.
Is that resistance between 6 and 14 battery disconnected?
U0073 seems to usually be the EBCM. One module is not connected to the can bus.
What about the maxi fuse next to the battery, that is the main power for the BCM.
Have you verified voltage on all fuses?
Did you test the voltages on 6 and 14?
This guy does a pretty good explanation. A little too much maybe.
https://www.youtube.com/watch?v=Jicb...MR.DIAGNOSTECH

NoHairRob

THAT WAS IT!!!!!!! The under hood fuse box has to be tightened till it clicks then tightened again till it won’t turn anymore!!!!!

donbrew

A Once a week solution.