Just in case it's a common problem, the rear screen heater stopped working on my 2003 V70. The AVO told me that I had 12v at one side and a connection to earth on the other. None of the heating elements were working, so it shouldn't be a break in the filaments. Eventually found that the earth connection was poor, too poor for the heater current, but enough for the AVO to see. Fitted a new independant earth, and all is OK now.