Parking sensors fault melting my brain

OK so hoping someone can help here as I'm pulling my hair out

2006, A6 Avante, Front and Rear parking sensors

I have the usual "put into reverse or press sensor button, display flashes and get a long beep"

I have gone down the normal route for testing -

Checked fuses, all OK
Unplug front sensors, test, no good, plug back in
Unplug rear sensors, test, no good, plug back in
Unplug front & rear, test, no good, plug back in
Tried new (second hand) module
Front bumper off, replaced all 4 sensors with new, tested with only front plugged in, nothing
Rear bumper off, replaced all 4 sensors with new, tested with only front plugged in, nothing

I have scanned the car with OBD Eleven, and have listed under faults -

1. Supply voltage for park assist sensor, open circuit/short circuit to ground
2. Supply voltage for park assist sensor, lower limit not reached

and also have under Live data - Ch 4 (resulting distance / vehicle speed and voltage
sensor voltage supply - 1.4v (this seems very low)

Any ideas anyone ?

Does anyone have a wiring diagram with wire colour codes as well ?

No, it shows all sensors as dead, even brand new ones

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Thanks for that, very helpful. Don't suppose you know/have the full wiring diagram/pin outs ?

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Oh and I assume the supply would be 12v ?

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