My 2015 Ford fiesta 1.0 Ecoboost has thrown up the engine light multiple times over the past year, each time reading P0420 catalyst efficiency below threshold bank 1. Ford advised I replace my catalytic converter and a local garage said it’s working fine. I am aware the O2 sensors on fiestas can be faulty. Any advice on what the issue could be and how to fix it? Thank you 🙂 

Possible exhaust leak near the o2 sensor

Possible upstream broadband hego sensor 

1 hour ago, scudney said:

Possible exhaust leak near the o2 sensor

Thank you for your reply! How would I confirm if this is he case? Can I find out myself or do I need to take it to a garage? 

1 hour ago, iantt said:

Possible upstream broadband hego sensor 

Thanks for your reply! I was told by the garage that if it was a sensor then a different code would show. Is there any way of knowing it’s a sensor and not the cat?