Mercedes M Klasse Diesel Starting Problem

I had a similar experience with my M Klasse, though I can't recall the exact year. The symptoms you describe, especially the brief start followed by immediate shutdown, strongly suggest an immobilizer issue. It's like a bouncer at a club; if the key doesn't have the correct 'password' it won't let the engine party! The error stored in the memory strengthens this case. Did you notice any issues with the remote start or the security light flashing erratically before the starting problem began?

That's a great analogy! Yes, the security light was flickering sometimes even when the car was off. And the remote start, while I rarely use it, had become unreliable recently, sometimes working, sometimes not. So you think it’s definitely leaning towards key programming? Any specific areas I should investigate or things I can try before calling in the pros?

Given the flickering security light and the intermittent remote start, it does sound like the key's communication with the ignition control module is compromised. While there are some DIY methods floating around, messing with the immobilizer can brick the system entirely, turning your car into a very expensive paperweight. My recommendation, based on experience, is to take it to a qualified workshop with Mercedes diagnostic equipment. They can properly diagnose the issue and reprogram the key or replace faulty components, if necessary. It is like performing surgery, if you are not a surgeon you should not cut.

I took your advice and went to a workshop that specializes in Mercedes. The key programming was indeed the culprit, as you suspected. They reprogrammed the key, and it's starting great now. Total cost was 45€! A massive thank you for steering me in the right direction and preventing me from making a costly mistake! I appreciate it.