Hi Keith,
Many ABS systems stop comms above a certain roadspeed, I suppose the decision in software is "now I need to concentrate on ABS control and not comms" but a pain nevertheless. One vehicle I repaired recently (can't remember which, but it was a diesel) stopped comms in first gear at idle speed which was a pain as I was fighting the engine management with the brakes to keep the speed down.
I had a rover 75 recently with ABS problems, when I scoped the rear wheel sensors I found one pulse per rev missing on the O/S/R which turned out to be a flake of rust stuck on the ASB bearing. In the end I had to remove the disks and descale the hubs to prevent the problem reoccurring.
HTH Shaun