Mercedes M Klasse Diesel Reduced Engine Power

I encountered a similar situation with my old 2018 Volvo V90. Reduced engine power and error codes sound like ECU problems. Have you tried a system reset or any diagnostics beyond reading the error memory? Any other electrical issues?

System reset as in disconnecting the battery? Yes, I've tried that. Cleared the code, but it returns after a short drive. Anything more involved?

I meant a more thorough diagnostic procedure. Since the fault code persists, I think you should see a qualified technician for a proper assessment. The issue might be more than a simple relay malfunction. Intermittent electrical problems are hard to diagnose without the right equipment. I advise against guessing at repairs, as it could make things worse. A defective control system can cause more harm than good.

Thanks for the input. You were right. The main relay in the ECU was faulty. 120€ later and it's running fine.