You would need to have the central electronic module scanned for codes to see if your issue is in the fuel pump sender side on the right side or the level sender that is on the left side of the tank. Did you have any work done recently where they had the pump out? Also did your vehicle have the fuel pump recall done? You may want to call Volvo and give them your vin number to see if you have an open recall. Only a few states had that recall. You can also ask Volvo if they are participating in the Volvo service for life where they give you a free diagnostic. At the very least they should be able to scan the vehicle for you for free. Here is the link for more info.
http://www.volvocars.com/us/top/yourvolvo/volvoserviceforlife/pages/default.aspx
Good luck and let us know how it goes.