2008 A4 Cabriolet - Wing mirror adjustment not working

[Sammyrai]

Hi, 

On my 2008 B7 A4 Cabriolet, one of the electric wing mirrors has stopped moving when I try to adjust it via the internal adjustment knob.

It's been like this for about 6 months. The strange thing is, over the past six months, I've tried it every week, hoping it would fix itself.

On two occasions, it moved a tiny amount before stopping again. 

 

There are no fault codes showing up. The other wing mirror works fine, via the same adjustment knob.

Can someone please guide me on how to diagnose what might be the problem? I don't know if it is wiring, the motor in the wing mirror itself, or something else completely. I'm good at most things car wise, except electrics!

All other electrics work fine.

Thanks! 

Sammy