Right, took the new sensor off today and put my old one back on. I cleaned it up first tho, and also used a washer on the top and put some sealant around it before I re-fitted it.....



Reset the ECU, started her up.....SUCCESS! No check engine light anymore, not even an intermittent one as of yet. So yeah, I must've bought a duff sensor, or one that's not compatible with my car. Still don't really know what the yellow dot on it means, and I don't think anyone else does either. So yeah, just wanted to say thankyou to everyone who's helped along the way, yet another problem sorted!

 

Intermittent check engine light is back today! Typical!

 

What this tells me is, original sensor faulty, new sensor over tightened and now fooked, old sensor refitted after a clean worked for a while but still fooked, while your mate did the job first time round he was a tad heavy handed and gave it a tug and dislodged the wire, wire now repaired 2x knackerd knock sensors.

Conclusion: try another knock sensor, and DO NOT OVER TIGHTEN