We were getting this fault code often . Oddly enough group of three and it was car number two. Ours would drop the calls and passengers would think they were stuck. It would restart on its own after about 30 seconds. Check communication wiring and shields. We were leaning to the CPU board, and of course you have to replace the CPU board in all three. One day the power supply failed on car number two, we replaced it and along with the DSP back up battery (on all three)and we have not had the complaint or the fault show up yet. That was about two months ago. Might just be coincidence,....and I am holding my breath now that I am typing this.