p0420
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Peugeot · SUVs
Catalyst System Efficiency Below Threshold (Bank 1)
Quick Answer
Error code P0420 on your Peugeot SUVs 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
Check for exhaust leaks with smoke test
2
Test oxygen sensors before and after converter
3
Measure converter efficiency with scope
4
Check engine timing and fuel mixture
5
Replace catalytic converter if failed test
Pro Tip
This issue typically requires professional diagnosis. Attempting this fix without proper training could cause further problems.
Parts You May Need
Catalytic converter
Oxygen sensors
Exhaust gaskets
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