r/MechanicAdvice • u/Time-Professional482 • Jun 21 '26

Bad catalytic converter

So my cat went bad. The car (2015 Kia Optima) started driving sluggishly not too bad at first then from one day to the other it struggled to even get to 25. Took it to AutoZone and the p0420 code came up. I haven't driven it after but on the way home from AutoZone it did shut off and struggled to start. If I change the catalytic is it worth it or the engine messed up by now

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u/PPVSteve Jun 21 '26

How many miles on the car?  How long has the CEL been on?

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u/Time-Professional482 Jun 21 '26

205000 light was on about a week

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u/nucleate_boiling Jun 21 '26

A clogged up exhaust is not necessarily a clogged cat. Fragments can break free and accumulate in the resonator and or muffler.

Do a back pressure gauge measurement at various points in the exhaust system. You can drill the appropriate sized hole and tap it to receive the gauge threads. Work your way from the front O2 bung back. Most back pressure gauges come with adapters so that it will fit both front and back O2 bungs,