p0420
Moderate
Genesis · Sedans
Catalyst System Efficiency Below Threshold (Bank 1)
Quick Answer
Error code P0420 on your Genesis Sedans means: Catalyst System Efficiency Below Threshold (Bank 1). This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Verify oxygen sensor operation with scan tool data
2
Check for exhaust leaks using smoke test
3
Measure catalytic converter temperature and efficiency
4
Perform engine compression test
5
Replace catalytic converter if efficiency below 85%
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Oxygen sensor
Catalytic converter
Exhaust sealant
Gaskets and clamps
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