If you have Haldex issues...
check out these pictures of an S3 in here yesterday with only fwd
Usual Earth strap broken and very corroded generally around the fixing..
Fixed by making up a new earth lead and replacing it.
Also... Check connectors for corroded pins..
Replacing both pin and socket in connector, with vag repair replacements, and the haldex pump started to work again and 4wd was once again working again.