Got a 98 V70 and the passenger side rear door, and sometime drivers side rear door, won't unlock. They will always lock and of course manually is fine. I am not sure what to search for to repair or what part to buy. Don't want to waste time and money on the wrong parts. Lock solenoid?
B

 

i have the same issue ,but only with the rear left door

 

New Lock assembly. Junk yard for 15 bucks. Removing the door panel and install is faily simple.

Check your fuses and relays, the silver ones that are hidden in the "auxillary" fuse box right next to the engine bay fuse box. It requires removal of a few extra torx bits if I remember correctly.

The Volvo mechanism is designed so if one little plastic part fails, the whole thing jams up and becomes inoperable.