Catalytic Converter Efficiency Below Threshold – Bank 1
Quick Answer
What P0420 Means
Your catalytic converter isn't cleaning exhaust gases efficiently. The downstream oxygen sensor detects that the converter is underperforming.
Most Likely Cause
Worn or failing catalytic converter
This is the cause in approximately 60-70% of cases
Catalytic converter replacement typically requires welding and professional installation.
Safe to drive short-term, but address within a few weeks. You may fail emissions testing.
Safe to Drive (Short-Term)
Safe to drive short-term, but address within a few weeks. You may fail emissions testing.
$400 - $2000
At a repair shop
$150 - $600
DIY (parts only)
Parts You May Need
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Detailed Diagnostic Information
Important Disclaimer
This information is for educational purposes only. We are not licensed mechanics. Always consult a certified mechanic for diagnosis and repair. Improper repairs can be dangerous.
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Last updated: 2025-11-26