A4 Wire Harness Ground Locations
 

Ok so all my error's are located on wire d80 on the wire harness. The systems that fall on this line are o2 sensor heaters, egr solenoid and EVAP purge valve. All sensors show 12.XX voltage going to them. I believe this is a ground issue. Besides the ground under the coolant reservoir and the 3 ground's bolted to the intake manifold has anyone ever dissected the wire harness itself? What I am looking for are the locations where there might be ground wires from various sensors soldered to another ground from another system. I need to know which end of the wire harness to start hacking up.

Also I know it is wire harness because replacing the ECU does not solve the issues.

If anyone has any experience dissecting a A4 wire harness let me know please.

Don't hack anything up. Get a wiring diagram and ohm out the wires. IIRC, all engine management stuff gets a "virtual ground" at the ECU.