Subaru 2002 IMPREZA Service Manual page 366

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)
ENGINE (DIAGNOSTICS)
Step
CHECK VEHICLE CONDITION.
CHECK ANY OTHER DTC ON DISPLAY.
T: DTC PO128
-
THERMOSTAT MALFUNCTION
-
DTC DETECTING CONDITION:
TROUBLE SYMPTOM:
CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(D0HC TURBO)-
49, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(D0HC TURBO)-46, Inspec-
tion Mode.>.
Two consecutive driving cycles with fault
Thermostat remains open.
Check
Has engine operated at idle or
has vehicle been driven with
part of engine submerged
under water?
Does the Subaru Select Moni-
tor or OBD-II general scan tool
indicate DTC PO125, P0301,
P0302, P0303, P0304, PO305
and PO306 at same time?
CHECK ENGINE COOLANT.
CHECK RADIATOR FAN.
1)Start the engine.
2)Check radiator fan operation.
Are coolant level and mixture
ratio of cooling water to anti-
freeze solution correct?
Does the radiator fan continu-
ously rotate for more than 3
minutes during idling?
Yes
In this case, it is
not necessary to
inspect DTC
P0128.
Go to step 3.
Go to step 4.
Repair radiator fan
Zircuit. <Ref. to
EO-46, Radiator
Main Fan and Fan
Motor.> and <Ref.
to CO-48, Radiator
Sub Fan and Fan
Motor.>
No
Go to step 2.
Inspect DTC
PO1 25, P0301,
P0302, P0303,
P0304, PO305 and
PO306 using "List
of Diagnostic Trou-
ble Code (DTC)".
<Ref. to EN(D0HC
TURBO)SO, List
of Diagnostic Trou-
ble Code (DTC).>
Replace the
engine coolant.
<Ref. to CO-25,
REPLACEMENT,
Engine Coolant.>
Replace the ther-
mostat. <Ref. to
GO-35, Thermo-
stat.>
EN(D0HC TURBO)-142