Subaru Legacy 2002 Service Manual page 654

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
No.
1 CHECK ANY OTHER DTC ON DISPLAY.
2 CHECK THERMOSTAT.
Step
Does the Subaru Select
Monitor or OBD-II general
scan tool indicate DTC
P0117 or P0118?
Does thermostat remain
opened?
EN-137
Check Yes
Inspect DTC
P0117 or P0118
using "17. List of
Diagnostic
Trouble Code
(DTC)". <Ref. to
EN-82, List of
Diagnostic
Trouble Code
(DTC).>
NOTE:
In this case, it is
not necessary to
inspect DTC
P0125.
Replace thermo-
stat. <Ref. to
CO-20, Thermo-
stat.>
Engine (Diagnostics)
No
Go to step 2.
Replace engine
coolant tempera-
ture sensor. <Ref.
to FU-29, Engine
Coolant Tempera-
ture Sensor.>