p0420
Moderate
Volvo · Sedans & Wagons
Catalyst Efficiency Below Threshold
Quick Answer
Error code P0420 on your Volvo Sedans & Wagons means: Catalyst Efficiency Below Threshold. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Likely Causes
How to Fix It
1
Scan for bank-specific oxygen sensor codes
2
Check for exhaust leaks visually and with smoke
3
Measure oxygen sensor voltage before and after converter
4
Test catalyst efficiency with diagnostic scan
5
Inspect catalytic converter for damage
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
Exhaust gaskets
Engine gaskets
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