Mercedes S Klasse window heater problems

Whoa, sounds familiar! I had a similar heating issue with my S Klasse. Rear window heater just quit, and the front wasn't great either. A discharged battery, really? Seems odd. Did you check the fuses?

The battery's condition seems to be the primary suspect, and I've checked the fuses. Were the symptoms identical, specifically the error code and diminished windshield heating? Was the window heater completely non-functional, or merely operating at a reduced capacity?

Yep, pretty much the same. The rear window heater was totally dead, no heat at all. And the windshield heating was weak, not like it used to be. I'd take it to a workshop, seems like the battery is the main issue. Good luck with your defroster repair!

Following your recommendation, I had the battery replaced. The rear window heating is now functioning correctly, and the windshield heating has returned to its normal performance. The total expenditure amounted to 290€. Thank you for your assistance.