I believe you are correct. And I also believe this method of injector rail pressure control is used in place of the mechanical prssure regulator of years past.

BTW - the fuel pressure sensors installed on many of the 2002-2003-ish S60/V70 cars were known for premature failure so Volvo approved a one-time replacement if needed. So if your's is acting up and/or triggering a check engine light, present your VIN number to Volvo customer care and see if you're eligible. I bought a high mileage V70 so when my sensor went bad I learned that it had already been replaced once under the recall. So the next replacement was on my nickel. Well, actually quite a few nickels.