Peugeot 301 NOx Sensor Failure

I have a 301 too. I had similar symptoms: check engine light and error codes pointing to the pollution control system. Maybe the catalytic converter? Is your air-fuel ratio ok?

Air-fuel ratio seems normal. Where exactly should I check for the cable or plug connection on the component itself?

On mine, the issue was definitely the NOx sensor connection after the catalytic converter. Given your symptoms, it's worth checking first. But you might need to visit a workshop anyway.

Thanks for the advice. The connection cable was indeed defective and has been replaced. Cost 95€. Now everything is fine.