GLK Transmission Failure

I have a similar GLK. I had a very similar thing happen. Check engine light, transmission acting up, wouldn't always start. Sounds like you're on the right track with the control unit. Did you check the transmission fluid level? Also, have you tried shifting to neutral and then back to park to see if it makes a difference? Mine would sometimes start in neutral when it refused to in park. Could be a faulty transmission sensor messing with the readings.

Thank you for your swift response. I did indeed verify the transmission fluid level, which appears to be within the acceptable range. Shifting to neutral, as you suggested, is an interesting point. I shall endeavor to test this and see if the engine starts in neutral. However, could you elaborate on your experience with the transmission sensor? Did you replace it yourself, or was it a task best left to a qualified technician?

Honestly, I fiddled with checking the neutral safety switch and sensor connections, but I'm no mechanic. Didn't fix anything. My issue sounds identical to yours. Eventually, I gave up and took it to my local independent Mercedes specialist. They confirmed it was indeed the control unit. Best not to risk doing more damage yourself. Get it properly diagnosed and repaired. Those transmissions are sensitive.

I extend my sincere gratitude for your guidance. I have heeded your counsel and entrusted my GLK to a trusted mechanic. As suspected, the control unit was indeed the root cause of the transmission woes. The unit has been replaced, and the vehicle now operates flawlessly. Thank you again for your invaluable assistance.