Had the dreaded oil low pressure warning going up hill, with pressure gauge not passing 60 psi.
My fix is volvo FSB 221-011, https://static.nhtsa.gov/odi/tsbs/2013/MC-10126589-9999.pdf
The problem is a Pressure Reductions (relief) valve craps out. My dealer had to order the parts at a cost of $79.96. It is on the oil filters housing on the bottom, cover closest to the engine. The SB will guide you in the repair. Simple to the point, 20 mins, 10mm socket, long extension and racket, and rags to clean up spill oil (not alot).