Subaru IMPREZA GD 2007 Series Manual page 238

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Diagnostic Procedure with Diagnostic Trouble Code (DTC)
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)-54, 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 parts, perform the Clear Memory Mode <Ref. to
EN(H4SO)(diag)-47, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)(di-
ag)-38, PROCEDURE, Inspection Mode.>.
Step
1 CHECK ENGINE COOLANT.
2 CHECK RADIATOR FAN.
1) Start the engine.
2) Check the radiator fan operation.
Check
Are the coolant level and mix-
ture ratio of engine coolant to
anti-freeze solution correct?
Does the radiator fan continu-
ously rotate for 3 minutes or
more during idling?
EN(H4SO)(diag)-129
ENGINE (DIAGNOSTICS)
Yes No
Go to step 2.
Replace the
engine coolant.
<Ref. to
CO(H4SO)-16,
REPLACEMENT,
Engine Coolant.>
Repair radiator fan Replace the ther-
circuit. <Ref. to mostat. <Ref. to
CO(H4SO)-27, CO(H4SO)-21,
Radiator Main Fan Thermostat.>
and Fan Motor.>
and <Ref. to
CO(H4SO)-29,
Radiator Sub Fan
and Fan Motor.>