Mercedes SLC Diesel Power Loss and Rough Idle

The symptoms you describe, including the error related to the fuel filter heater, reduced power, and rough idle, do point to a potential issue within the fuel system. The error code strongly suggests investigating the cable and plug connection for the fuel filter heater. Has the fuel filter been replaced recently? Sometimes, a poorly installed or incompatible filter can trigger similar issues.

The fuel filter was replaced about ago. I didn't do it myself, a local shop handled it. Should I check the filter itself, or just focus on the cable and plug connection first? Is there a specific way to check the connection, or should I just look for obvious damage?

Given the symptoms and error code, it would be prudent to inspect the cable and plug connection first. Look for any signs of corrosion, damage, or loose connections. If everything appears to be in order, then consider revisiting the fuel filter itself. However, since you mentioned power loss and rough idle, and considering the stored error, it is advisable to take the vehicle to a workshop for diagnosis. Trying to self-diagnose fuel systems on modern diesel engines without proper tools can lead to further complications.

I had a look at the cable and plug – couldn't see anything obvious, so I took it to my usual garage. Turns out, it was indeed the fuel filter heater connection. They replaced a faulty connector and cleared the error. Cost me 95€, but the power is back, and it's idling smoothly again. Thanks for pointing me in the right direction!