Do I need a rebuild?
 

Background
2011 Ralliart
Roughly 103k
Mods: AEM intake, CXRacing intercooler with piping & bov, and a Cobb 3 port


So my SES light came on yesterday right before i headed on a 3 hour round trip to pick up a downpipe. No issues driving with light on. Scanned the code this morning and pulled a U0100 chassis code and a P1871 transmission code.

According to my scanner thats a manufacture specific code. Obd-data website says its a "Undefined Gear Ratio" code Transmission mechanical transfer case 4x4 switch circuit short to battery. (P1871)

Code U0100 is a "Lost Communication with ECM/PCM A"

Cleared it hoping it was just a false alarm but the codes came back after a drive around town. Do i need a rebuild or can it be saved?

Okay, did some digging and found that OBD website gave me wrong info on code P1871. Code P1871 is APS System (Signal Abnormality) Step one is to check all CAN Bus connections.. Any idea how i can do that with a usb to OBD or tactrix openport?

But wait it gets better! Step three is replace transmission assembly (smiley poop emoji)

If it does come down to that im erasing the code at a dealership and trading her in...