P0128Powertrain
Coolant thermostat — temperature below regulating temperature
Where to start
The engine takes too long to reach operating temperature. Almost always the thermostat. It affects fuel consumption noticeably.
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 thisFault code P0128: the thermostat or the sensor
Step by stepHow to tell whether the thermostat is to blame
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 «Intake measuring sensors»
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.
The heater blows coldThe engine is warm but the heater blows cool or barely warm air. Sometimes one side is warmer than the other; sometimes it only gets warm while driving.Fuel consumption has gone upYou refuel noticeably more often for the same driving. The lamp is usually off — the unit thinks it is coping.Slow to warm up, the heater blows coldThe temperature needle sits low for ages, the cabin stays cold, and on the motorway it gets worse. Consumption rises noticeably.The cooling fan runs all the timeThe fan roars right after starting and does not stop even on a cold engine or in frost.
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.