P0420 – Catalyst System Efficiency Below Threshold (Bank 1)
Description
The catalytic converter efficiency is below the required threshold on Bank 1. This means the converter is not reducing harmful emissions effectively, usually due to wear, contamination, or exhaust issues.
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Compare Diagnostic ScannersSymptoms
- Check Engine Light illuminated
- Reduced engine performance
- Increased fuel consumption
- Strong sulfur smell
- Failed emissions test
- Possible rattling noise
Causes
- Worn or damaged catalytic converter
- Exhaust leak before the converter
- Faulty oxygen sensors
- Long-term rich or lean fuel mixture
- Engine misfires
- Overheated or damaged converter
- Contaminated fuel or oil burning entering the exhaust
Diagnosis
- Check O2 sensor readings
- Inspect catalytic converter temperature
- Check fuel trims
- Inspect for exhaust leaks
Repair
- Replace catalytic converter
- Fix exhaust leaks
- Replace faulty O2 sensors
- Correct fuel mixture issues
- Repair misfires to prevent future damage
