2015 Audi A4 (B8.5) - Constant 5.7V on 5V Reference

Hey everyone, hunting a bizarre wiring short on a 2015 Audi A4 2.0 tdi 190ps . and wanted to see if anyone has encountered this specific failure point before I strip the entire loom back.

The Core Symptoms:

The car was doing an excessive amount of DPF regenerations. On vcds calculated soot mass was always quite high measured 90% of the time is in the negatives which is impossible oil ash at 30g

Checking live data showed a permanent 5.7V on the 5V sensor reference line. I got new dpf sensor.after unplugging lots of sensors i

Swapped in a second-hand ECU, and the constant 5.7V remains, ruling out a blown internal ECU voltage regulator or bad remap / adblue delete

If the reference pin at the back of the DPF pressure sensor is physically depinned/isolated, the operations of the pressure sensor return to normal functions (or pretty much normal functions).

The Breakthrough:

While troubleshooting, I moved/wiggled the main wiring harness inside the static plenum/cowl chamber (roughly 4 to 8 inches away from where it exits the ECU box).

Moving this specific section instantly triggers clicking relays, flashes the glow plug light on the dash, and throws "overvoltage to glow plugs

Current Conclusion:

It appears a constant 12V supply wire (ignition feed or relay trigger) has chafed, melted, or cross-shorted directly into the 5V reference wire inside that wrapped plenum chamber bundle, back-feeding and overpowering the circuit.

My Questions for the Forum:

Has anyone seen this bundle short out inside the static plenum chamber before? Is there a sharp factory clip or edge inside there known for slicing the tape?

Does anyone happen to know which specific 12V feed runs parallel to the 5V reference line in

this exact stretch so I know what color wires to hunt for?

Any wiring diagrams for a 2.0 tdi a4 190ps or past experiences with this specific bundle would be massively appreciated!