I had a similiar issue, my S60 did not shut off thoug, it happened that while driving it would stutter, almost like a fuel filter clog. It threw a code that read Fuel Pressure too high at the Fuel Rail. It did this a few times at stoplights, on the freeway when I got on her. So I took her to the dealer, dreading the outcome, it was a simple Fuel pressure sensor that was dying. The cost was $375. Took 45 minutes to replace and another 20 to wash and vacuum my car. Marin Volvo, Grant Bos, is a great Service Writer. It looked easy enough, yet to find the problem you need VADIS to read the proprietary codes, or a good Service Writer at your dealer who will tell you what it is. VFL, TurboBrick-4-eva!
2004 S60 2.5T
2007 XC90 V8 Sport