Subaru LEGACY 2006 Manual page 171

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Diagnostic Procedure with Diagnostic Trouble Code (DTC)
ENGINE (DIAGNOSTICS)
AA:DTC P0128 COOLANT THERMOSTAT (ENGINE COOLANT TEMPERATURE
BELOW THERMOSTAT REGULATING TEMPERATURE)
DTC DETECTING CONDITION:
• Detected when two consecutive driving cycles with fault occur.
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-55, DTC P0128 COOLANT THERMOSTAT (ENGINE
COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE), Diagnostic Trouble
Code (DTC) Detecting Criteria.>
TROUBLE SYMPTOM:
Thermostat remains open.
CAUTION:
After repairing or replacing the defective part, perform the Clear Memory Mode <Ref. to EN(H4SO)(di-
ag)-43, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)(diag)-34, PRO-
CEDURE, Inspection Mode.>.
Step
1 CHECK VEHICLE.
2 CHECK ANY OTHER DTC ON DISPLAY.
3 CHECK ENGINE COOLANT.
4 CHECK RADIATOR FAN.
1) Start the engine.
2) Check the radiator fan operation.
Check
Was the vehicle driven or idled
with the engine partially sub-
merged under water?
Is any other DTC displayed?
Are the engine coolant level
and mixture ratio of cooling
water to antifreeze solution
correct?
Does the radiator fan continu-
ously rotate for more than 3
minutes during idling?
EN(H4SO)(diag)-134
Yes No
In this case, it is Go to step 2.
not necessary to
inspect DTC
P0128.
Check DTC using Go to step 3.
"List of Diagnostic
Trouble Code
(DTC)". <Ref. to
EN(H4SO)(diag)-
70, List of Diag-
nostic Trouble
Code (DTC).>
Go to step 4. Replace the
engine coolant.
<Ref. to
CO(H4SO)-12,
REPLACEMENT,
Engine Coolant.>
Repair radiator fan Replace the ther-
circuit. <Ref. to mostat. <Ref. to
CO(H4SO)-23, CO(H4SO)-17,
Radiator Main Fan Thermostat.>
and Fan Motor.>
and <Ref. to
CO(H4SO)-25,
Radiator Sub Fan
and Fan Motor.>