p0420
Moderate
Kia · Sedans
Catalyst System Efficiency Below Threshold (Bank 1)
Quick Answer
Error code P0420 on your Kia Sedans means: Catalyst System Efficiency Below Threshold (Bank 1). This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Likely Causes
How to Fix It
1
Connect OBD-II scanner and monitor oxygen sensor data
2
Inspect exhaust system for leaks
3
Check catalytic converter for blockage or damage
4
Test oxygen sensors upstream and downstream
5
Clear code and perform diagnostic drive cycle
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
Catalytic converter
Oxygen sensors
Gasket sealant
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