Seat Cordoba Diesel Rough Running

Rough running and a check engine light? Sounds familiar! I had similar issues with my old Opel Astra, although it was a petrol engine. The error codes pointed to fuel trim issues and misfires. Have you checked your airflow sensors? A faulty sensor can wreak havoc on the fuel mixture and cause the engine to run poorly. Also, what onboard diagnostics tools are you using? A generic OBD2 scanner might not give you the full picture. You might need a tool that can read manufacturer-specific codes.

Airflow sensors seem fine, at least according to my basic OBD2 reader. What do you mean by fuel trim issues exactly? And how did you fix it on your Astra?

Fuel trim is basically the engine control unit's ECU way of adjusting the fuel mixture to compensate for deviations from the ideal air-fuel ratio. Short-term fuel trim STFT and long-term fuel trim LTFT indicate how much the ECU is adding or subtracting fuel. If the values are too high or low, it suggests a problem. In my case, it turned out the injector was faulty, like yours. The ECU couldn't compensate anymore. I'd recommend getting the injectors properly tested and potentially replaced. Trying to force a reset procedure on a faulty injector won't fix the underlying problem. A workshop is probably your best bet here.

I took it to the shop. They confirmed the injector issue and performed the reset procedure after replacing the faulty injector. Cost me 515€, but it's running smoothly again. Thanks for the input!