The passenger rear door on the left will not open...

Child locks are suited just under lock you must open door to see it,have orange colur. If you could not open the door,try to open from inside when car is locked with remote control. the doorlock could be broken a usual problem.it could also be one relay to the left rear of car. this on s60model.

Hey, i had the same problem, the way the lock works inside the door is that there is a screw that works as an axle but after so many times being open and closed, the screw comes undone and the screw falls out and the lock stays locked.

I don't believe I have seen a Volvo four door hatch-back here in the US, but my guess would be child-proof locks on the rear. Open the front doors and look for any switches on the front edge of the back doors. If there aren't any, check the owner's manual before contacting your dealer.