1993 gmc z71 4x4 , 350 engine, 4l60e auto trans..... Getting code 28 which shows quad-driver module (computer) circuit #2 fault..

Any help with this would be appreciated, i just purchased this truck and can tell the engines been out, found the knock sensor unplugged which fixed the code 43 that i also had, now i only have a 32(egr circuit fault) and a 28(quad-driver module (computer) circuit #2 fault)

dont feel the egr code will have anything to do with the 28, i know quad drivers are in the pcm, i also know that the code doesnt mean a bad pcm right away so what im wondering is what is this circuit so maybe i can look in a general direction for a loose or off ground wire