The most likely cause of this is the brake pressure sender fault
Done plenty of these
The pressure sender is bulit into the hydraulic section of the ABS unit and is not sold separately
I've seen companies doing recon units but more hassel than they are worth in my experience (and not a great deal cheaper)
When the fault was first occurring VW required us to replace the complete unit including the control unit
If this is the case the part was nearly £1000 Inc vat, but it gradually become cheaper
But they are now selling the Hydraulic section (one at fault) separate , last time I checked this part was around £300
This part can be fitted at home without the use of the diagnostic machine
Fit it, bleed fluid system, road test until lights go out
Job done.