# 0420



## Blasirl (Mar 31, 2015)

A code* P0420* may mean that one or more of the following has happened: 

Leaded fuel was used where unleaded was called for (unlikely) 
A damaged or failed oxygen / O2 sensor 
Downstream oxygen sensor (HO2S) wiring damaged or connected improperly 
The engine coolant temperature sensor is not working properly 
Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe 
Failed or underperforming catalytic converter (likely) 
Retarded spark timing 
The oxygen sensors in front and behind the converter are reporting too similar of readings 
Leaking fuel injector or high fuel pressure 
Cylinder misfire 
Oil contamination

Read more at: P0420 Catalyst System Efficiency Below Threshold


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