p0420
Moderate
Mazda · SUVs & Crossovers
Catalyst System Efficiency Below Threshold (Bank 1)
Quick Answer
Error code P0420 on your Mazda SUVs & Crossovers 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
Verify oxygen sensor readings are normal
2
Check for exhaust leaks around converter
3
Perform back pressure test on catalytic converter
4
Check fuel trim values with scanner
5
Replace catalytic converter if failing
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 sensor
Exhaust gasket
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