Aidan,
You are of course correct. There is a problem with the oxygen sensor so the first step is to correct this.
The problem I have is the car is a traders car. He is reluctant to spend money when there is a possibility the PCM is faulty. If it comes to this he will scrap the car due to the other repairs needed.
Not the best situation for a committed diagnostic repair.
I was hoping to understand why there is 1.6v on the signal wire from the PCM. maybe it is a diagnostic bias voltage? In line with what you say, maybe its there because an open circuit is detected in the heater circuit.
I will take another look on Tuesday.
Thanks for your reply,
Kieron