Just found this on another thread:

"Well, I think that we've finally solved the no start issue with my XF (knock on wood). This problem had been occurring for a couple of months and a few weeks ago the car stalled at a light and wouldn't start. In the end, a local dealer (Koons in Tysons Corner, VA) replaced the Relay Control Module. This module actually contains 4 control modules (including the fuel pump module) but is a single unit. Evidently a very easy fix in the end. You open the rectangular box next to the battery and the module is the part with the 40 amp fuse, 5 or 6 other fuses, and 4 or more connectors. You pop out this entire unit, disconnect all the connectors, pop it back in and close the box. Since I got my XF back on Monday, it's started every time and, maybe it's my imagination, but seems to be running better than ever."