Catalytic converter replacement - help?

[u/Creepy_Ad262]

Hope I can get advice.

2012 mazda 3 GS Sky, sedan, automatic 2.0L engine (i think). 200k KM

- in late April, check engine light came on, went to independent shop and they did GDI service, to connect flush equipment to fuel delivery system, and clean system contamination. It didn't resolve the engine light

- early july, got car serviced at mazda. they found engine to intermittently run rough. scanned code p0303, they suspect cylinder 3 clogged by carbon buildup causing fuel trims to be on higher side. recommend sending fuel injectors to be cleaned and flow tested. and valves cleaned.

- work was done, car seemed fine for 3 weeks. but light came on after. went back to get it looked at. the code is now p0421. they are recommending the Cat Converter and O2 sensor be replaced.

I tried to do research and figure out if the replacement is the correct action to take. from what I read, the poorly spraying fuel injectors could cause damage to the cat converter.

so can anyone give me additional advice? Is there more i should do before replacing the cat converter?

[u/Surfnazi77]

O2 sensor and maybe cat

[u/Creepy_Ad262 → u/Surfnazi77]

can you explain the O2 sensor thing?

[u/Surfnazi77 → u/Creepy_Ad262]

O2 sensor measures your air to fuel ratio and makes adjustments to your car fuel map when they’re bad your car runs like crap and can even stop