I have a 2018 1.0L fiesta and the check engine light came on last week. After getting an OBD reader on it I got a P0420 catalyst below threshold, I get a garage to do a full diagnostic and find the cat itself has failed not a sensor, not ideal but oh well.
I’ve just done a few miles for a necessary drive and the check engine light has gone off. Has anyone else had this? Surely a broken cat can’t just fix itself?
I have a 1.0L 2016 Fiesta too, and about a year ago, I got a P0420 code. A few months later, I noticed a rotten egg smell, and after checking the OBD2 O2 sensor data, it confirmed the cat was bad or clogged.
I haven’t gotten around to fixing it since it passed the emissions test, and the drop in MPG wasn’t too bad. After a spirited drive to work one day, I noticed the code cleared itself. It came back after regular driving, but I can clear it again by driving aggressively for a day or two.
So, yes, if there’s just a little carbon or exhaust buildup, it can reduce the cat’s efficiency, triggering the P0420 code. The ECM will keep checking for efficiency loss, but if it doesn’t find any (because you’ve cleared the buildup by driving hard), the light will turn off after two checks.
Try putting a tank of V-Power in, adding a bottle of Lambda cleaner, and driving hard for a week. If your cat isn’t too damaged (like mine might be), it shouldn’t cause you too many issues for a while.
And by “driving hard,” I mean flooring it to 5000+ rpm on a slip road, open road after a roundabout, etc. Hope this helps!
I have the same issue with my 2016 Fiesta, same model year and engine, and it’s been happening for the last 50,000 km. At first, the check engine light came on, stayed on for a few hundred km, and then went off, only to come back later. Now, it’s always on unless I clear the error codes using the Torque app, but it comes back after a few hundred km. The car runs fine, and I pass the emissions tests, but it’s definitely annoying. Unfortunately, it didn’t fix itself. Sorry!
As long as it’s not causing back pressure or affecting the inspection, you should be okay!
On the other hand, my dad’s Ford had a strange issue—after running weird for a few seconds, it suddenly exploded a 5-inch chunk of the exhaust pipe right before the cat. We think it was caused by back pressure, fumes, and heat.
Using premium fuel and installing new spark plugs could improve your efficiency and help clear the check engine light. Premium fuel allows the engine to run a leaner tune, which reduces the workload on the catalytic converter.
Those are just some tips from my experience as a former owner of a late-model EJ25 Subaru.
1.0 ecoboost moment:sparkles: