Yes but no joy. I think it’s the O2 lamda sensor. When I disconnected the sensor downstream of the DPF I got out of bounds errors on sensor 4. I had replaced the sensor immediately upstream of the DPF. No change. So that must be sensor 3. Hence O2 sensor 2 with sensor near turbo as sensor 1.
I replaced the sensor immediately upstream of the DPF having watched a YouTube video which proved misleading. Having watched the video I believed a bad sensor had Infinite resistance. Open Circuit. Whilst a good sensor would show a resistance across the two terminals.
This is not the case. Having still in my possession the old sensor I decided to apply heat to the tip using a gas soldering iron with the hot air tip. Sure enough, during heating the resistance dropped from infinite to something readable. I’ve now bought a removal tool to get the O2 sensor out whereupon I can test it. Meanwhile the wife is not too happy as I’m using her car.