SOLVED! No Crank, No Start, Communication Codes Present

[TJBaker57]

Code B1001 GMC Description The Inflatable Restraint Sensing and Diagnostic Module (SDM) stores the vehicle's restraint ID from the Vehicle Identification Number (VIN) and the last 4 digits of the SDM part number. When the ignition is turned ON, the SDM compares this information to the information stored in the Body Control Module (BCM) over the General Motors Local Area Network (GMLAN) communication circuit. If there is a mismatch between the information stored in the SDM and BCM, Diagnostic Trouble Code (DTC) B1001 will be set.

This may answer a pondering of mine. Over the years I have seen the SDM (SIR, Airbags, whatever) request a portion (characters 2,3,4,5) of the VIN early in the powerup sequence. (even though the BCM broadcasts the entire VIN at powerup).

Maybe has something to do with this comparison?

 

[TJBaker57]

@cope1980

I got the BCM today and after a cursory visual I checked the resistance across connector 1, A3 and ground to compare against my own readings. Yours read about 275k ohms where mine read around 175k ohms. I began looking at solder joints and following traces. After a bit I had the ohmeter hooked up again and noticed the reading was 175k. Jumped some power to it and the relays clicked. Connected the serial data line to one of my test beds and I could talk with the BCM. However it is intermittent.






Tomorrow I will see if I can isolate a bad solder joint maybe?

 

[cope1980]

I believe my issue is resolved. Replaced the BCM with a used eBay BCM and had it flashed at the dealer.
There were a few codes that were historical and with the help of TJBaker57, I was able to get the codes cleared and all is well with the Envoy.

TJBaker57 is most definitely the GURU. I appreciate his time and expertise in helping me solve this issue!

 

[TJBaker57]

For completeness sake when time permits I will detail what we did behind the scenes here. So if someone has a similar issue later these details may be of use.