G Klasse auxiliary battery error

I own a G Klasse and encountered a similar situation with the auxiliary battery system. The symptoms you described, including the error message, weak starting, and the stored error code, strongly suggest an issue with the auxiliary battery. In my case, the low voltage triggered a series of electrical malfunctions. Have you tested the auxiliary battery's voltage? A significant voltage drop is often the culprit.

Thanks for the quick response. I haven't tested the voltage yet. I'm not entirely sure where the auxiliary battery is located in the G Klasse, or how to properly test it. When you mention 'voltage drop,' what's a typical voltage range I should be looking for in a healthy auxiliary battery? Any tips on how to access it and safely check the voltage?

The auxiliary battery is typically located under the passenger seat or in the engine compartment, depending on the specific configuration of your G Klasse. A fully charged 12V auxiliary battery should read approximately 12.6 volts or higher. Anything significantly below 12 volts indicates a potential problem. Given your lack of experience with electrical testing, I recommend consulting a qualified technician. Continuing to drive with an unresolved auxiliary battery issue can potentially damage other electrical components. The battery failure eventually cost me 290€ to fix.

Thanks a lot for the advice! I understand now. I'll take it to a workshop to have the battery checked and replaced. It's good to know what to expect regarding the cost too. Really appreciate the help!