Subaru Legacy 2002 Service Manual page 1378

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
No.
1 CHECK ANY OTHER DTC ON DISPLAY.
Step
Is there any other DTC on
display?
EN(H6)-171
Check Yes
Inspect the rel-
evant DTC using
"List of Diagnostic
Trouble Code
(DTC)". <Ref. to
EN(H6)-87, List of
Diagnostic
Trouble Code
(DTC).>
NOTE:
In this case, it is
not necessary to
inspect DTC
P0139.
Engine (DIAGNOSTICS)
No
Replace rear oxy-
gen sensor. <Ref.
to FU(H6)-46,
Rear Oxygen
Sensor.>