p0420
Moderate
Subaru · SUVs & Crossovers
Catalyst System Efficiency Below Threshold (Bank 1)
Quick Answer
Error code P0420 on your Subaru 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
Connect OBD-II scanner and confirm code
2
Check oxygen sensor readings before and after catalyst
3
Perform visual inspection of catalytic converter
4
Check for exhaust leaks
5
Review engine misfire history
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
OBD-II scanner
Oxygen sensors
Catalytic converter
Gaskets and sealant
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