You are referring to the upstream (Pre cat) sensors then? There are two, one for each bank. Follow the exhaust pipes from the turbos back towards the cats and you cant miss them, they are right on the top of the pipe about (I guess) 1.5-2ft away from the motor.
'04 XC90 2.5T AWD (Angus) 134K. '99 S80 T6 (Medusa) 214k. On borrowed time LOL '98 V70 T5 (Vivienne). RIP @ 228K. Spun rod bearings.