p0420
Moderate
Mitsubishi · Sedans & Cars
Catalyst System Efficiency Below Threshold (Bank 1)
Quick Answer
Error code P0420 on your Mitsubishi Sedans & Cars 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
Test both oxygen sensors before and after catalytic converter
2
Inspect exhaust system for leaks
3
Check fuel pressure and injectors
4
Monitor fuel trim values
5
Perform catalytic converter efficiency test
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
Oxygen sensor
Catalytic converter
Exhaust gaskets
Related Error Codes