You don't have to drain it. Some oil may come out, but if you stuff a rag under the sensor you should be able to catch it. If oil does drain out, it's a good idea to top the reservoir back off after you install the new sensor.
I think the one on top is a pressure sensor?? The one Im speaking of is at the bottom backside drivers side? I need to replace and think I read you have to drain reservoir. Maxx
Cant find the "link", but i did downloadthe pic, but cant get it posted...anyway, the EOT is on back/driver side, at top, the EOP is on top of hpop, and the IPR is down bottom driver side on back of hpop...guess i cant post attachments..argh