P0121Powertrain
Throttle position sensor A circuit range/performance
Where to start
The throttle position sensor does not agree with the air flow. Usually a dirty throttle plate or the connector. Start by cleaning the throttle and checking the connector; replace the part last.
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
We have a detailed piece on thisThrottle position sensor: P0121, P0122, P0123 and P2135
Step by stepUnstable idle — how to find the cause
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
All codes in «Throttle and accelerator pedal»
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.