I had a surprise the other day: while troubleshooting an ECM-250A code on my 2004 S60 NA, I found that on my Equus-3160 scanner, in "Live Data" mode, it showed the fuel pressure! With engine running or not. Maybe the '01s will also do that.
On my '04, the ECM-250A code said "O2 sensor level too high or too low". Reading on this forum about the vacuum lines and especially the right-angle rubber peices, I checked them and the one coming from the intake mainfold to the air box (which is used to operate the hot/cold intake air vent gizmo) had a leak. The right-angle rubber piece which connects the hard-line vacuum line to the intake manifold was deteriorating (right on schedule at 104K miles). It had become waxy and non-flexible, and almost crumbled when I tried to remove it. The other right-angles seemed OK, I think it's the ones mounted directly on the hot engine that are the first to go. The engine seemed to be running OK, only a slightly rough idle, but the check-engine light had come on, which prompted me to break out the code reader.
Hope this helps.