What else should i check for a p0420 check engine light with a running fine car?

[Scott22]

My 2017 Outback’s check engine light came on yesterday, and it’s running perfectly fine. I borrowed a basic scanner and the only code it’s throwing is P0420, which points to the catalytic converter. I’m just wondering if there’s anything else I should check before assuming that expensive part has gone bad.

[Mark_C]

I had a P0420 on a 2017 Outback a while back. The car ran fine, but the light stayed on. In my case it wasn’t a brand-new cat; the downstream O2 sensor started reading funny after a tiny exhaust leak near the flange. We fixed the leak and swapped the sensor later, and the light behaved after that.

[William20]

Sometimes it’s just sensor drama. I’ve seen downstream sensors throw that code even when the catalytic converter is still good. A rough highway drive and a reset sometimes buys you time, but that’s not a fix.

[LoganEL]

I’d look for an exhaust leak around the cat area or a misfire that quietly inflates fuel trim. Those things can fool the computer into thinking the cat isn’t doing its job.

[Kyle.B]

Have you checked for an exhaust leak around the cat?