Hi folks. Thanks for reading my post!

In short, there is 1.6v on the black wire (pin 4) of the oxygen sensor.

Vehicle:-
Audi A3, 1.6 (AKL engine code), Simos PCM, year 2000, pre EOBD

Faults:-
027B Oxygen sensor heating faulty – permanent
020D Oxygen sensor signal implausible – permanent

Live Data:-
Reports 1.6v whether the sensor is connected or not. Plugged in, the voltage may drop a little to 1.2v when revved.
On my KTS 520 there is no fuel trim info. I should have checked OBD!

Checks:-
Open circuit on the sensor heater wires.
NBV at sensor heater circuit.
1.6v at pin 4 loom side whether the sensor is connected or not, using sensor ground and battery ground.
Battery earth volt drop to engine 0.01v.
Run engine with sensor disconnected and use DMM to check sensor output. At idle output = 0.9v. I disconnect the EVAP pipe to the manifold to introduce an air leak and the voltage drops to 0.4v. The sensor seems to be responding OK.
Cut the wire at the PCM (pin 25, black wire) and live data still reports 1.6v, confirmed with DMM.

Conclusion:-
The PCM is defective.
The heater side of the oxygen sensor is defective.

Questions:-
1, would anyone agree with my conclusion?
2, why is there 1.6v at the sensor wire?
3, have I missed any checks?

I didn't consider a bias voltage input at the time, however I feel this would of showed up when the sensor was plugged in (unless it was open circuit, which it was not since it produced a voltage unplugged)?

The car failed the MOT on emissions and other issues. The customer is likely to scrap the car if the problem is the PCM.

Many thanks,
Kieron