Subaru Legacy 2003 Service Manual page 526

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)-129
ENGINE (DIAGNOSTICS)
Yes
Inspect the rele- Replace throttle
vant DTC using position sensor.
"List of Diagnostic <Ref. to
Trouble Code FU(H4SO)-30,
(DTC)". <Ref. to Throttle Position
EN(H4SO)-83, List Sensor.>
of Diagnostic
Trouble Code
(DTC).>
NOTE:
In this case, it is
not necessary to
inspect DTC
P0121.
No