C4 Knock Sensor Issue

I had similar symptoms on my Opel Astra, though it was a few years older. The warning light and uneven idling were the first things I noticed. In my case, the garage found corrosion in the knock sensor wiring. Before replacing the sensor itself, I would meticulously check the wiring harness and connector. Is there any visible damage or corrosion?

Thanks for the tip! I haven't checked the wiring myself yet, but the mechanic mentioned it as a possibility. Where exactly is the knock sensor located in the C4? And how difficult is it to access the wiring?

Unfortunately, I'm not familiar with the Citroen C4 specifically. On the Astra, it was quite difficult to access without proper tools and knowledge. Given the potential for misdiagnosis and the importance of proper ignition timing, I would strongly advise taking it to a qualified workshop. A faulty knock sensor can cause serious engine damage if ignored. It's better to be safe than sorry.

Thanks for your advice! I took your suggestion and brought the C4 to a workshop. They confirmed it was indeed the knock sensor connection, just as you suspected. They cleaned the contacts and secured the wiring. Cost me 95€, which is way better than replacing the whole sensor! Really appreciate the help!