Nick,
haveyou vag com'd your car?
If there is no power to the haldex im sure the light comes on the dash...
Mine with the esp turned off... grips and wants to hang its **** out in the snow so im sure its working.
I thought mine wasnt working either, had to read the manual and they mentioned something about driving below 40kph for the system to work. Also, Hadlex needs oil to engage the wet multi-plate clutch system, check ABS sensors too.
The pumps usually break on gen.1 haldex sooner or later, unfortunately quite often sooner.
Vag-com will not give a fault code on this problem, the only way to test it is by measuring the resistance in the pump. Don't know if this is a common problem over there, but up here the Haldex is used way more because of the snow. Unfortunately I've heard lots of ppl having this problem, and it's not a cheap part.
Let's hope anyway that it's something else than this.
Im pretty certain about the answer to the question im about to ask but just want to make sure.
Would a knackered/faulty haldex cause me tobe down on power?