P0136Powertrain
Downstream O2 sensor circuit malfunction (bank 1)
Where to start
The circuit of the oxygen sensor after the catalyst is faulty. This sensor does not control the mixture, it watches the catalyst, so the car drives as usual. Check the connector and the wire under the floor — road salt and stones get at them there.
What to watch in live data
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
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.