P0420Powertrain
Catalyst system efficiency below threshold (bank 1)
Where to start
The catalytic converter works below par. Before replacing it, make sure the second oxygen sensor is fine and there is no exhaust leak — those get replaced far more often.
A code is not a diagnosis. It says which check failed, not which part to replace. Clearing it without repair only means the car will report it again in a few trips.
How to put together a report a mechanic will actually read
We have a detailed piece on thisFault code P0420: the catalyst or just a sensor
How the code is built
Letter — the systemPowertrain: engine and transmission
Common or the maker's ownGeneric code: the same on every car
Which part of the engineEmission controls: catalyst, EGR, fuel vapour
Number of the faultThe serial number inside that group — it does not say how serious the fault is
All codes in «Catalytic converter»
How it feels behind the wheel
The same fault shows itself in different ways. Each sign below says what to look at in the live data.
How the app helps
CarScan reads this code from your car through an OBD-II adapter, shows whether it is active now or only stored, names the module that reported it, and puts it into a plain-text report for your mechanic.