Mercedes R Klasse Diesel Engine Power Loss

Reduced engine power and a fault code definitely point to something going wrong. I had a similar issue with my old Audi. The dashboard light was on and it felt like the engine was choking. Did the scan tool give you any specific fault code numbers? Knowing the exact code is crucial for diagnosing the problem. Have you tried clearing the fault code to see if it returns immediately or only after driving for a while?

The scan tool gave me a generic fault code, something like 'Engine Performance Reduced'. I did try clearing the error memory, and the check engine light stayed off for a short drive, but came back on after a few kilometers. Any ideas what that might indicate?

Okay, if the light comes back on after clearing the fault code, it confirms that the underlying problem is still present. The generic code suggests it could be a number of things, but given the history of chip tuning, that's a likely culprit. The tuning might be causing the engine to run outside of its designed parameters, triggering the fault code and reduced power. I'd recommend taking it to a workshop with experience in Mercedes diesels. They can run a more comprehensive diagnostic with a better scan tool and properly diagnose the issue, and possibly remap the ECU if necessary. It may also be worth getting an independent inspection to determine if the tuning has caused any damage to the engine.

Took it to the workshop as suggested. They confirmed the ECU had been messed with. They reflashed it back to the original Mercedes settings. Cost me 180€, but the engine's running smooth again, and the dashboard light is gone. Thanks for the help!