P0457Powertrain
Evaporative leak — fuel cap left loose
Where to start
The unit says it plainly: the fuel cap is open or not sealing. This is the kindest code in the whole reference — it names the cause, not the place. Tighten the cap until it clicks, clear the code and drive for a few days. If it returns, look at the cap's seal: it dries out and costs pennies.
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 fuel cap: codes P0455, P0442 and P0457
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 «Fuel vapour leaks»
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.
It smells of petrolA fuel smell in the cabin or around the parked car. Sometimes with the Check Engine lamp on.Check engine came on after refuellingYou filled up, drove a few kilometres, and the light came on. The car drives exactly as before.
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.