Subaru Legacy 2004 Service Manual page 444

ENGINE (DIAGNOSTICS)
(1)
(1) Front oxygen (A/F) sensor
(2) Rear oxygen sensor
(1)
(3)
Electrical Component Location
(3)
(4)
(2)
(3) Front catalytic converter
EN-02091
EN(H4SO 2.0)(diag)-12
(4) Rear catalytic converter
(2)
(4)
EN-02092
EN-01973