I have my girlfriend's 2015 Chevy Sonic 1.8L with a list of codes.
It went out to a shop to get the head gasket replaced and try to diagnose these codes that started showing up shortly before the head gasket blew. And really we don't know if the head gasket was the issue in the first place.
Symptoms:
The car will intermittently have plumes of white smoke under load and obviously lose power, but it will clear up and run like nothing happened.
Steps taken to diagnose:
I've replaced the ECM, only to find the same P0641 code. I've also replaced the Multifunction Intake sensor as well given the various baro and IAT codes. I'm unable to find any issues with the wiring harness with an oscilloscope or volt meter.
I only have a 2013 Model year service manual so I'm unsure if they've changed what's on the 5V reference A circuit.
Questions I pose to the reader:
Does anyone have a more up to date service manual that can tell me the sensors on this circuit?
Maybe there's a problematic area in the wiring harness that I can check?

 

This ended up being a short with the AC pressure sensor. I removed the AC compressor to replace the oil pressure switch. The sensor's wires was caught under one of the bolts when I went to reinstall the ac compressor.