P0420Catalyst System Efficiency Below Threshold (Bank 1)
The catalytic converter is not cleaning the exhaust gases efficiently. The upstream and downstream O2 sensors show similar readings.
This code also has a manufacturer-specific definition:
Can I keep driving? With caution
You can drive to the shop, but do not postpone the repair. The problem may worsen and damage other components.
Sistema Afectado
Sistema de Escape · Catalizador y sensores O₂
La falla se localiza en la línea de escape: catalizador, sondas lambda (O₂) o sistema EGR.
Espacio para vendedores de repuestos
Aún no hay un anunciante en este espacio.
Symptoms You Will Notice
What you may observe when this code appears
- Check Engine light on
- Possible sulfur (rotten-egg) smell
- Failed emissions test
- Slight power loss
Possible Causes
The components or conditions that trigger this code
- 1Deteriorated or damaged catalytic converter
- 2Faulty oxygen sensor
- 3Exhaust system leaks
How to Fix It — Step by Step
Recommended diagnostic and repair procedure
- 1Check the oxygen sensors with a scan tool
- 2Inspect the exhaust for leaks
- 3Test the catalyst efficiency
- 4Replace the catalytic converter if needed
Note: This information is for general reference. For precise diagnostics and safety repairs, always consult a certified mechanic.
Estimated Cost
Approximate range in USD (varies by region and shop)
Catalytic converter + diagnosis
* Diagnosis only: $50–$150
Quick Info
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