Cm2250 Exh backpressure/coolant level code

[HamblinTrucking]

I have searched through and have not found exactlty what I am experiencing. Before buying a new wiring harness for this thing, I wanted to make sure its not something stupid first.

2013 KW T660
Demand@ted by someone reputable here
(codes were there with previous crap delete)
Recent overhaul (leads me to suspect wiring issue)

Heres the issue, it has 2374 code (exhaust gas pressure low voltage or shorted to ground) and 0197 (low coolant, valid data but low)
I have replaced the sensors, inspected the wiring, tested the wiring between the ecm and the sensor, changed the pigtail(coolant level pigtail) etc.

One thing that stands out the me is, they have a ground jumper wire going from the nox power connector by the ecm, to the nox sensor on the engine. If you unplug that connector the ecm wont come on(not sure if that is normal or not but seemed odd to me). I cut the ground wire going to that nox sensor off and it shows 10 volts on it. According to the cummins wiring diagram, I also unplugged all the ecm return grounds from the sensors that share the exhaust backpressure sensor ground, and tested it at the ecm connector with it unplugged from the ecm. In theory according to the wiring diagram it should just be a dead pin, but, it still has a ground.

This truck apparently has had a new ecm put in it (doesnt look like it to me at all) before I got it.

Im not too sure what to think. I am hoping its just something I am missing.