2011 Mercedes E250 CDI 2.1L Fault Code P0685: Diagnosis and Repair Guide

Hi everyone, I own a 2011 Mercedes E250 CDI with a 2.1L engine. Recently, my car has triggered a fault code P0685. The vehicle starts normally and runs without any noticeable performance issues, but I'm concerned about the underlying cause. What steps should I take to diagnose and resolve this issue? Is P0685 related to fuel system components or sensor malfunctions? Any insights from owners of similar models would be greatly appreciated. Thank you in advance for your help.