P0420Severity: Low
P0420 – Catalyst Efficiency Below Threshold (Bank 1)
The catalytic converter is not meeting expected efficiency.
What it means
Based on the upstream and downstream oxygen sensors, the catalytic converter's efficiency has dropped. It is most often an aged catalyst or an oxygen sensor issue.
Symptoms
- Check-engine light
- Failed emissions test
- Slight power loss
- Sometimes odor
Common causes
- Aged/faulty catalyst
- Faulty downstream O2 sensor
- Exhaust leak
- Engine burning oil/coolant
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Frequently asked questions
What does trouble code P0420 mean?
P0420 – Catalyst Efficiency Below Threshold (Bank 1). Based on the upstream and downstream oxygen sensors, the catalytic converter's efficiency has dropped. It is most often an aged catalyst or an oxygen sensor issue.
Can I drive with a P0420 code?
It's usually not urgent, but finding and fixing the cause matters for emissions and fuel economy.