PO410 is the secondary air injection system. More that likely, your secondary air injection pump has gotten wet and therefore has failed in some form or fashion. My '98XC threw me the same code this weekend. Go to http://www.volvospeed.com/bay13.htm for more info about this system and how to replace it. It's a common problem and sooner or later most of us 90's brick owners experience this problem. For most every code, go to www.codereader.com there you will at least find a generic description of what most code numbers are.