I had a similar problem on my Mk3, the ABS light was stuck on, and it was throwing up a 'ABS hydraulic pump fault' on the OBD scan , however after some digging with the diagram and meter, it turned out to be the light module that was causing the fault. There was a comparator chip which had failed in mine. As soon as I disconnected it and re-scanned - no fault present. Replaced the module, all is ok.