I have a 2004 Volvo S60 2.5T, which needed its power steering fluid topped off. The owner’s manual simply states “ATF”, so that’s what it got, and the car hasn’t complained one bit.
However, in follow-up I did some “research” online and now I’m confused and frightened 
I read everything from “NO! Don’t use ATF you will ruin the steering system” to “ATF is fine”. One post says that after 2005 all Volvos use Pentosin CHF 11S or Volvo P/N 30741424 and you can tell because it’s clean/green. (Well, the reservoir is black plastic and I haven’t stuck my finger in it yet to find out what color it is). Anothe post says that the new fluid went into use after 1999.
Is everything ok or do I need to flush/fill the power steering lines?
First off, don’t pay any attention to internet forum posts when replacing or topping up fluids. ALWAYS follow the manufacturers recommendations.
All you have to do is read that owners manual and it will tell you exactly what to use and how much.
If you do not have this book, phone or go to your nearest dealer and ASK what is supposed to be used.
Supply information needed: the year/make/model/engine size and whether automatic or standard trans.
I hate to pay volvo prices for fluids, but I don’t take any chances with my 2004 S80. Th PS fluid at the dealer is about $18.00 for a 1 liter bottle.
I would flush and refill with the correct fluid. It’s not worth the risk of messing something up. Check out the prices of getting your volvo repaired, and you will see what I mean.