Mercedes X Klasse diesel engine overheating issue

Whoa, overheating is never good! Okay, so the check engine light and overheating points to something serious. When you say 'active air flap,' are you talking about the ones in the grille that open and close? If they're stuck closed, that would definitely cause overheating because it messes with the whole cooling system. Have you noticed if they're visibly stuck? Is it happening all the time, or just when you're driving hard?

Yeah, the ones in the grille. I haven't physically checked their position, but I will. Does the frequency matter? Does it indicate anything specific?

Okay, so if they're stuck closed even sometimes, it'll restrict airflow and you'll get overheating especially when the engine is working harder. I'd recommend taking it to a workshop. A faulty grille shutter can cause the car overheating. They should be able to diagnose it properly and check the whole cooling system. Ignoring overheating is risky.

Thanks for the advice. Took it to a workshop and you were right, it was the electromechanism on the active air flap. Cost 590€ to repair.