Post cat signal, Pico example waveform shows it should be near zero volts, scoped an 08 ford Ka and it was found to be as waveform suggested.

Cannot remember the the exact code number but the description was "mixture lean"

Tried earthing on the sensor earth and it made no difference.

Interestingly the front sensor was switching between 0.3 and 1.2 volts with battery earth and dropped to 0.1 and 0.9 volts with sensor earths however both sensors generated a fault code for voltage low using their earths ???

Car back next week, will give it an on road check and report back.