They did not go out at the same time. You most likely have some bad contacts in the ABS module ......I had the same issue and swapped out each speed sensor 1 at a time on all 4 wheels to no avail (I have several xfires) so no cost to me and it didn't fix the issue so I started tracing down the wiring and found the large (44 pins) connector on the drivers side connected to the brake regulator/ABS system was not seeing the signal and causing the error codes with the speed sensors. I disconnected the connector and reseated it in the ABS module and reconnected the battery and all was well again. This just happened 1 sunny day for no reason so I do not know what caused the short but it was a relatively easy fix and I am pretty sure both sensors going out at the same time is unlikely.