Mercedes M Klasse Transmission Issues Resolved

Implausible shifting, transmission light, emergency mode sounds like limp mode. Undervoltage can absolutely play havoc with the TCU. Worn transmission oil, especially in a 7G-Tronic, can cause similar symptoms. Have you checked the oil level and condition? Is it dark, burnt smelling? A simple oil replacement might help, but if there's significant wear, a complete transmission flush might be necessary. When was the last time you had the transmission serviced?

Okay, limp mode, got it. I haven't actually checked the transmission oil myself. Honestly, I'm not really sure how to do that properly on this car. I bought it used a few years back, and I don't see any record of a transmission service in the paperwork. Is checking the oil level something I can do myself without special tools, or is it best left to a professional?

Given you don't have service records and aren't familiar with checking the level, I'd strongly advise against DIYing it. Modern transmissions are sensitive, and getting the fluid level wrong can cause more damage than good. Dropping the pan on a 7G-Tronic is straightforward, but you'll need a dipstick tool specifically for Mercedes transmissions to check it properly. Best bet is to take it to a reputable shop that knows Mercedes transmissions. They can check for codes, assess the oil condition, and advise on whether an oil replacement or a full transmission flush is needed. If it is undervoltage, they'll identify the cause too.

Thanks for the advice! I took it to a local shop, and they confirmed the transmission oil was indeed pretty worn. They did a transmission oil replacement, and that seems to have sorted it out. Cost me 240€ all in. The shifting is much smoother now, and the transmission light hasn't come back on. I appreciate the help!