2018 Sorento P0420 Code - Catalytic Converter Efficiency Low

ClearTheCode guidance (Kia · Diagnostics & codes)

Summary: For 2018 Sorento P0420 Code - Catalytic Converter Efficiency Low, work through these steps on your 2016+ vehicle:

1. Confirm the symptom — note when it happens (cold start, highway, after fuel fill, etc.).
2. Scan codes — save all pending/stored DTCs; don't clear until you've recorded them.
3. Check TSBs & recalls — look up your VIN for open campaigns and known fixes.
4. Inspect the obvious — related fuses, connectors, fluid level, and recent repairs.
5. Test the common fix — follow model-specific service procedures; one change at a time.
6. Escalate if needed — burning smell, no brakes, overheating, or stalling in traffic → shop visit.

Owner reported: My 2018 Kia Sorento EX, with about 85k miles, just threw a Check Engine Light. I scanned it with my OBD-II reader, and it's showing a P0420 code: "Catalyst System Efficiency Below Threshold (Bank 1)".

I haven't noticed any major performance issues, maybe a slight dip in MPG, but nothing dramatic. Could this really be the catalytic converter already, or is there something else I should check first…

This is educational guidance, not a substitute for hands-on diagnosis.