Any ABS problem outlining an individual component like a valve is usualy a bad solder joint in the ECU or more often bad continuity in the flexible ribbon that takes power from the circuit board to the inlet and outlet valves in the valve block. Over the years I have repaired many of these faults, I would say that 90% of ABS module faults are repairable. The valves them selves are very reliable and are only used when ABS is required. A lot of info on the net now available (see link)