Wind rear ventilation flap issue

Indeed, a faulty rear ventilation flap is a known issue on the Wind. Have you checked the relevant fuses and relays for the climate control system? Also, can you retrieve the exact error code from the ECU? That would help narrow down the possible causes.

I haven't checked the relays yet. Where exactly are they located? Also, I don't have the equipment to retrieve the error code myself. Is there a way to diagnose it without special tools?

The relays are typically located in the engine compartment fuse box and possibly under the dashboard. Without diagnostic tools, it's difficult to pinpoint the exact cause. Given the symptoms and your suspicion of a wiring issue, it may be best to visit a workshop for a proper diagnosis. The repair including parts should be around 95€.

Thanks for the info. I'll take it to a shop and have them check the relays and error codes as you suggested. Sounds like the quickest way to resolve it.