I am experiencing the same issues as OP so I suspect the BCM is the issue but was looking for confirmation before I start swapping parts.
While driving, instrument gauges went to zero, multiple warning lights and messages illuminated (seems like all of them), then cycled back to normal. No effect of driveability or performance. Car shut off normally when start/stop button pressed.
Next day, car started normally but same thing happened with gauges and warning lights. Engine did not immediately shut off when start/stop button pressed. Gauges and warning lights kept cycling and eventually engine shut off within a minute. Delayed response to pressing start/stop to turn on ignition. Played around with pushing the start/stop button with and without pressing the brake pedal. Finally got it to start and drive but gauges and warning lights were still erratic.
Ran scan tool and came up with codes below.
Car will now only start with remote start but will not go fully “on” and unlock steering wheel & transmission selector when brake pedal and start/stop button is pressed. 1 out of 5 times will respond to pressing start/stop button. Other times, I just hear 2 relay clicks (not starter) when I press the start/stop button. When it does come on, gauges are in US units but HVAC is in metric (Celsius).
2015 GMC Yukon 5.3L
DTC codes 2/15/2022
Engine Control Module – Pass
Transmission Control Module – Pass
Electronic Brake Control Module (EBCM)
U0073-00/History DTC – Control Module communication bus A off
U0077-00/History DTC – Control module communication chassis expansion CAN bus off
U0102-00/History DTC – Lost communication with transfer case control module
U0126-00/History DTC – Lost communication with steering wheel angel sensor module
U0151-00/History DTC – Lost communication with inflatable restraint sensing and diagnostic module
Power Steering Control Module (PSCM)
U2099-00/History DTC – High speed communication enable circuit
Body Control Module (BCM)
B305A-00/Current DTC – No response from steering column lock received
B3978-00/Current DTC – No environment identifier received from inflatable restraint sensing and diagnostic module
B3979-00/Current DTC - No environment identifier received from HVAC control module
B3980-00/Current DTC - No environment identifier received from instrument cluster
U0078-00/Current DTC – Control module communication low speed CAN bus off
U0100-00/History DTC – Lost communication with engine control module
U0121-00/History DTC - Lost communication with electronic brake control module
Human Machine Interface Module (HMICM)
U0029-00/Current DTC – MOST bus performance