I just want to add....from '95-'99 excluding '99.Maybe for '91-95 also but i'm not sure,except for rear o2 which is not present in pre '95 cars.There are some rare models of 850 which use Titania o2 sensors.
Our cars use Zirconia.
History of Volvos in the family:
'71 144 S
'73 144 De Luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS
'97 850 2.5 20v / fully equipped / Motronic 4.4 from the factory / upgraded with S,V,C,XC70 instrument cluster / polar white wagon