Mercedes C Klasse Diesel Engine Issue

Rough running and drift compensation errors usually point to fuel injection issues, likely a faulty injector. I've seen similar on the same model. Have you checked the airflow sensors? Sometimes a dirty sensor can throw the fuel trims off and cause misfires. Also, when was the last time you ran a decent fuel system cleaner through it?

Airflow sensors seem clean on visual inspection. I haven't tried any fuel system cleaner, to be honest. What exactly does 'drift compensation' even mean in this context? Is it something I can fix with a system reset, or am I looking at a bigger problem?

Drift compensation is the ECU trying to correct for inconsistencies in fuel delivery between cylinders. A system reset won't fix a faulty injector. While it might temporarily clear the code, the problem will return. Based on the symptoms and code, a faulty injector is highly probable. Best to get it properly diagnosed at a workshop.

Thanks for the advice. Took it to the workshop, and you were spot on. It was indeed a defective injector. They replaced it, ran some diagnostics, and did a software revision. Bill came to 515€. Runs smooth as silk now.