p0420
Moderate
Mazda · Sedans
Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your Mazda Sedans means: Catalyst System Efficiency Below Threshold Bank 1. This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Scan for related fault codes and inspect oxygen sensors
2
Check for exhaust leaks using smoke test
3
Monitor oxygen sensor output with scanner
4
Test catalytic converter efficiency
5
Replace catalytic converter if necessary and clear codes
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
Gaskets and seals
Related Error Codes