Mercedes M Klasse Diesel Solar Sensor Issue

Sounds familiar. I had a similar sunlight sensor issue with my old Audi A4, though it manifested slightly differently. Are you sure it's just the solar sensor? Sometimes other temperature sensors can play a role in the climate control system’s behavior. Have you checked those too? And what exactly does the error code say? That might give you a better idea of what's going on before you start replacing parts or paying for labor.

That's a good point about other temperature sensors potentially influencing the climate control! How would I go about checking those additional temperature sensors? Also, the error code itself is rather vague, simply stating 'Solar Sensor Fault'. Is there a way to get more granular information from the system, or am I at the mercy of what the diagnostic tool provides?

With a vague error code and potentially multiple sensors involved, honestly, you might be better off taking it to a workshop with proper diagnostic equipment. They can usually pinpoint the exact wiring or sensor that's causing the problem. Could save you money in the long run, rather than chasing down possibilities. Then you can decide if you want to tackle the repair yourself after they've identified the culprit.

I did end up taking the car to a workshop, as you suggested, and you were right! It was indeed a faulty cable connection to the solar sensor. The 95€ estimate was spot on. Thank you for your advice!