Mercedes B Klasse Diesel Generator Problem

I had a similar issue with my B Klasse. The symptoms you describe, particularly the reduced power and the flickering lights, strongly suggest an alternator issue. Think of it like a water pump failing to supply enough coolant; the engine overheats. Similarly, a failing alternator can't supply enough electrical power. Before condemning the alternator entirely, double-check all the wiring connections to it. A loose or corroded connection can mimic a failing alternator. Also, make sure the serpentine belt tension is correct. Is the belt routed correctly? Is the tensioner working properly? A slipping belt won't drive the alternator efficiently. Did you measure the alternator output voltage? What voltage are you seeing at idle and under load?

Thanks for the input. I'll recheck the wiring and belt tension as you suggested. When you experienced this, did it also cause the 'car won't start' problem? The diagnostic pointed directly at the generator, and I'm leaning towards replacing it, but I'm trying to eliminate all possibilities before I commit. I haven't measured the alternator output voltage yet, but I will do that now. Can you elaborate on what you mean by 'under load' when measuring voltage?

Yes, the failing alternator was definitely the cause of the 'car won't start' issue in my case. The battery was simply not getting charged. 'Under load' means with electrical consumers switched on – headlights, air conditioning, heated rear window. This puts a greater demand on the alternator. If the voltage drops significantly under load, it confirms the alternator's inability to keep up. Given the symptoms and the diagnostic code, it does sound like the alternator is the prime suspect. While you could try rebuilding it, for the cost and effort, replacing it with a new or remanufactured unit might be the most reliable solution in the long run. I'd recommend taking it to a trusted workshop. They have the proper tools and expertise to diagnose and repair the charging system correctly.

Appreciate the confirmation and the advice. I rechecked everything you mentioned, and the alternator output was indeed low, especially under load. I took it to a workshop as you suggested. They confirmed the alternator was defective and replaced it. Total repair cost came to 960€. The car is now running perfectly. Thanks again for your help!