My Yukon ended up in a water filled ditch up to the windshield.

No it didn't get up that far. It did get up to fuse block for doorlocks and such.

Need to scan test ECM to see it it will communicate with scanner... And check for trouble codes plus view live data.... Your best bet is a mechanic that will make a house call.. There is no protocol for this type repair!... Good luck with it!! ..BTW, if it had gotten into the dash... It would be a total loss!!!! Can't fix that, never would get it right again!!

Ok thank you.