horstheld1

Mercedes M Klasse auxiliary battery issue

My 2014 Mercedes M Klasse with a gasoline engine is showing an auxiliary battery error on the speedometer, and it's also stored in the error memory. The engine start is sluggish, like the battery is weak. Could the auxiliary power system not be charging the battery properly? What steps can I take to diagnose this?

4 comment(s)

Sounds like a classic auxiliary battery failure. Is the car struggling to start, or are other car electronics acting up? These batteries don't last forever, and a weak one can cause all sorts of weird issues with power management. Have you tested the voltage of the auxiliary battery?

I have not tested the voltage of the auxiliary battery myself. Where is this battery located in the vehicle, and can I access it without specialized tools? I am apprehensive about delving too deeply into the car electronics myself.

Given your apprehension about car electronics, and the symptoms you're describing, it's probably best to take it to a workshop. A weak auxiliary battery can affect engine start and other systems. It really does sound like the battery is not holding a charge, or is simply kaput. It's worth getting a professional diagnosis to avoid causing further damage.

I took it to a local workshop, and they confirmed that the auxiliary battery was indeed faulty and not charging. The repair cost was 290€. Replacing it resolved all the error messages and electrical malfunctions. Thank you for pointing me in the right direction!

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