Car Ka 2003, Dura Tec (Lambda sensor with grey plug)

Hello I have a Ford KA that was running fine, I thought I would change the plugs, oil and air filter as part of a service.

Its really puzzling me as the car was running fine before and never had any issues.

Since I have done this, right away on the second start up the engine check light has come on, I just though I may have knocked a multi plug or something, when removing the spark plugs or the air box.

I run a scan on the car and its coming up P0030 H02S Heater Control Circuit B1-S1.( pre cat manifold one)

I checked all the multi plugs and connectors and all looked ok, I spent ages doing this and have wasted so much time, I just conceded that it must be just unlucky and the lambda sensor has packed up.

Or is there something I could have knocked? all looks fine?

I went to Euro car parts and they supplied me with a FAE Lambda 77253, the plug was not right on this so I has to use the old one, I fitted this and cleared the codes, the light cam right back on, same code P0030.

I quickly tested the multi plug that goes to the sensor and I am getting around

4.3v on the yellow and black wire, and 12v on the yellow and purple wire, these go to the white wires of the sensor.

Is there any other tests I can do?

Does anyone know these cars inside out and have an idea on the wiring.

Really gutted, thank you.