P0135Powertrain
O2 sensor heater circuit malfunction (bank 1, upstream)
Where to start
The heater of the oxygen sensor before the catalyst is not working. Check the fuse and the connector first: without heating the sensor takes a long time to start working and the car runs rich.
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 thisThe oxygen sensor: telling from live data that it is tired
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 engineFuel and air metering
Number of the faultThe serial number inside that group — it does not say how serious the fault is
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.