Subaru 2009 IMPREZA Service Manual page 1232

(1) Front oxygen (A/F) sensor
(2) Front catalytic converter
Electrical Component Location
(1)
(3) Rear oxygen sensor
(1)
EN-00303
(3)
(4)
EN-01933
EN(H4DOTC)(diag)-11
(2)
(3)
(4)
ENGINE (DIAGNOSTICS)
(4)
EN-06854
Rear catalytic converter
(2)
EN-01800