Subaru Legacy 2004 Service Manual page 557

Diagnostic Procedure with Diagnostic Trouble Code (DTC)
Step
1 CHECK ANY OTHER DTC ON DISPLAY.
Check
Is any other DTC displayed?
EN(H4SO 2.0)(diag)-125
ENGINE (DIAGNOSTICS)
Yes
Check DTC using Replace the rear
"List of Diagnostic oxygen sensor.
Trouble Code <Ref. to FU(H4SO
(DTC)". <Ref. to 2.0)-33, Rear Oxy-
EN(H4SO gen Sensor.>
2.0)(diag)-66, List
of Diagnostic Trou-
ble Code (DTC).>
NOTE:
In this case, it is
not necessary to
inspect DTC
P0139.
No