Subaru Legacy 2003 Service Manual page 558

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
Step
1 CHECK ANY OTHER DTC ON DISPLAY.
Is any other DTC displayed?
Value
DTC indicated.
EN(H4SO)-161
ENGINE (DIAGNOSTICS)
Yes
Inspect the rele- Replace rear oxy-
vant DTC using gen sensor. <Ref.
"List of Diagnostic to FU(H4SO)-43,
Trouble Code Rear Oxygen Sen-
(DTC)". <Ref. to sor.>
EN(H4SO)-83, List
of Diagnostic
Trouble Code
(DTC).>
NOTE:
In this case, it is
not necessary to
inspect DTC
P0139.
No