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Check Engine Light P0420 on my 2020 G70 3.3T - Catalyst Efficiency

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Ashley M. · rep 0 · May 25, 4:34 AM · 1 replies · solved · Question

Hey everyone, I've got a P0420 code popping up on my 2020 Genesis G70 3.3T Sport. The Check Engine Light came on a few days ago, and I used my cheap OBD-II scanner to pull the code. It says "Catalyst System Efficiency Below Threshold (Bank 1)".

The car seems to be running fine, no noticeable loss of power or strange smells. Fuel economy might be slightly worse, but it's hard to tell for sure. I've cleared it once, and it came back after about 50 miles of driving.

Is this definitely a bad catalytic converter, or could it be something else like an O2 sensor? Any tips on what to check before taking it to the dealer? I'm still under warranty but hoping for a quick fix if possible.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:34 AM

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ClearTheCode guidance (Genesis · Diagnostics & codes)

Summary: For Check Engine Light P0420 on my 2020 G70 3.3T - Catalyst Efficiency, work through these steps on your 2015+ 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: Hey everyone, I've got a P0420 code popping up on my 2020 Genesis G70 3.3T Sport. The Check Engine Light came on a few days ago, and I used my cheap OBD-II scanner to pull the code. It says "Catalyst System Efficiency Below Threshold (Bank 1)".

The car seems to be running fine, no noticeable loss of power or strange smells. Fuel economy might be slightly worse, but it's hard to tell for sure. I'v…

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

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