Quest Headlight Range Control Issue

Sounds like a real pain. That auto-leveling system can be finicky. Does it try to adjust when you first start the van? Sometimes you can hear the little motors whirring. Also, have you checked the connections to the headlight units themselves? A loose plug can cause all sorts of weirdness.

Yes, it attempts a brief adjustment with a faint whirring sound on startup. Connectors at the headlight units seem secure and free of corrosion. Could the servomotor itself be the problem, and can it be repaired separately, or does it require a whole headlight assembly replacement?

That whirring but still malfunctioning definitely points to the servomotor inside the headlight. Unfortunately, they're usually sealed units. While maybe you could find a replacement motor and DIY it, honestly, it's a huge hassle and you risk damaging the headlight further. Given the error codes and the adjustment issue, I'd say bite the bullet and take it to a trusted workshop. They can properly diagnose it and confirm, but it really sounds like the servomotor. They'll have the right tools and knowledge to replace the whole headlight assembly if needed.

Took it to a workshop, and it was indeed the servomotor within the headlight assembly. Repair cost was 1040€.