p0420
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Hyundai · Sedans
Catalyst Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your Hyundai Sedans means: Catalyst Efficiency Below Threshold Bank 1. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Accent SE 2022Azera Limited 2022Elantra SEL 2024Elantra Hybrid SEL 2024Elantra N 2024Elantra Limited 2024Elantra N Line 2024Elantra SE 2024Ioniq 6 Limited 2024Ioniq 6 SE Long Range 2024Ioniq 6 SE Standard Range 2024Ioniq 6 SEL 2024Sonata Limited 2024Sonata N Line 2024Sonata SE 2024Sonata SEL Plus 2024Ioniq 6 SE 2024Ioniq Hybrid Blue 2022Sonata SEL 2024Sonata Hybrid SEL 2024
Likely Causes
How to Fix It
1
Connect OBD-II scanner and confirm P0420 code
2
Inspect catalytic converter for physical damage or rattling
3
Check downstream oxygen sensor wiring and connectors
4
Verify engine timing is correct
5
Replace catalytic converter if confirmed faulty
Pro Tip
This issue typically requires professional diagnosis. Attempting this fix without proper training could cause further problems.
Parts You May Need
Catalytic converter
Oxygen sensor downstream
Exhaust gasket
Sensor socket tool
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