My 2011 mustang with 94k miles was getting a P0420 code and no other codes. The only symptoms were slight loss of acceleration and power. No misfires though. Took it to mechanic today. Used the scanner and we couldn’t find any obvious faults. Fuel trims were good, oxygen sensors were fine (computer said no fault detected for both o2 sensors) and no obvious culprits for this p0420 code.
We tried doing fuel system cleaning service with seafoam and then reset the code and i’ve driven 50-60 miles since then but I can still feel the loss of power/hesitation when accelerating. The code hasn’t come back yet but pretty sure it will since the car feels exactly the same.
I’m starting to think the catalytic converter is clogged if the o2 sensors are fine. Wouldn’t that be the only other possibility for p0420?
My question is; Why would the catalytic converter fail after only 94k miles? Did my spark plugs at 88k or so. Typically cats don’t just die out with age unless they’re overheated or have a rich/lean condition which I don’t have either of. I am thinking I should just replace the cat but I know if I don’t diagnose the issue that caused it to fail in the first place, the new one will fail again. I’m just not sure where to start. I can rule out a rich or lean condition since fuel trims were normal and spark plugs since I did them 6000 miles ago.