I have, to this point, had pleasurable times wrenching on my Wifes new (2003) Forester 2.5. Front sensor went in with ease.cured code for 5 min (front heater) then set code for rear heater. get ND sensor, jack up look for sensor, where did they hide this thing? thanx

Top of the second cat back just past the trans. It sticks up toward the left side of the car. You can follow the wiring for it down the left side of the trans. The connector has a tab that sticks it to the side of the trans just above the rear trans cross-member.

https://www.google.com/search?q=03+forester+o2+sensor&safe=off&client=safari&hl=en&source=lnms&tbm=isch&sa=X&ei=2mX_U7OOBJT7oQSVroDACQ&ved=0CAgQ_AUoAg&biw=320&bih=356#facrc=_&imgrc=iQGHo1iMeaIujM%253A%3BowlbTDgx6TsoTM%3Bhttp%253A%252F%252Frepairguide.autozone.com%252Fznetrgs%252Frepair_guide_content%252Fen_us%252Fimages%252F0996b43f%252F80%252F20%252F47%252F10%252Fmedium%252F0996b43f80204710.gif%3Bhttp%253A%252F%252Fwww.autozone.com%252Fautozone%252Frepairguides%252FSubaru-Forester-1998-05%252FComponent-Locations%252FHeated-Oxygen-Sensor-H02S%252F_%252FP-0996b43f8037f2b2%3B500%3B272

Thank You