Peugeot 206 Knock Sensor Issue

I had similar symptoms on my Opel Astra a while back: check engine light, bad fuel efficiency. It turned out to be a faulty sensor connection. Did you check the harness for corrosion or damage?

You mentioned a faulty sensor connection. Was it visibly corroded, or did you have to do some more in-depth testing to find the issue?

I didn't see any visible corrosion at first glance. A mechanic found that the contacts inside the plug were slightly bent and not making proper contact. I would suggest you also go to a workshop.

I inspected the plug as you said, and the contacts were a bit loose. I took it to the workshop and they confirmed the faulty connection. Repair cost me about 95€ to replace the harness connector. Now, the engine runs smoothly, and the check engine light is gone!