The tailgate on my Audi A6 avant ultra SE will not open with the drivers door switch or the button or the key fob. I can only open it manually from crawling into the boot . However oncr the tailgate is raised c4" the motorised system will raise it and also close it completely. Any ideas?

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Hello  Graham,

Could be barking up wrong trees, but starting to work once it’s part way open could be significant. 
Potential trouble spot ( but your vehicle may not be old enough) is the fracturing of wires in the flexible harness section twixt tailgate and body. When the tailgate is partly open the wires may just touch enough to make contact. Worth an eliminating-look at. 
Of course, it could just be a fault tailgate lock. 
Kind regards,

Gareth. 

Thanks for the info. I shall check the harness first.