DTC P0128: Coolant Thermostat (Engine Coolant Temperature Below Thermostat Regulating Temperature): Notes
- -
DTC detecting condition:
Detected when two consecutive driving cycles with fault occur.
Trouble symptom:
- Thermostat remains open.
- Coolant temperature rises slowly.
NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>Basic Diagnostic Procedure>PROCEDURE .
- CHECK DTC
.
- Turn the ignition switch to ON.
- Using the Subaru Select Monitor or a general scan tool, read the DTC of [Engine]. Ref. to COMMON (diag)>DIAGNOSTIC TROUBLE CODE (DTC)
.
Is DTC other than P0128 displayed? (Current malfunction)
Yes : Check the appropriate DTC using the 'Diagnostic Trouble Code (DTC)'. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>Diagnostic Trouble Code (DTC)>LIST .
No : Go to 2.
- CHECK ENGINE COOLANT
.
Check the engine coolant. Ref. to COOLING (H4DOTC)>Engine Coolant>INSPECTION .
Is the check result OK?
Yes : Go to 3.
No : Refill the engine coolant. Ref. to COOLING (H4DOTC)>ENGINE COOLANT .
- CHECK RADIATOR FAN
.
- Start the engine.
- While keeping idling for approx. 3 minutes (with accelerator OFF), check the operation of the radiator fan.
Does the radiator fan continuously rotate for 3 minutes or more during idling?
Yes : Repair the radiator fan system. Ref. to COOLING (H4DOTC)>RADIATOR FAN SYSTEM .
No : Go to 4.
- CHECK ENGINE COOLANT TEMPERATURE SENSOR
.
Check the engine coolant temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>Engine Coolant Temperature Sensor>INSPECTION .
Is the check result OK?
Yes : Replace the thermostat. Ref. to COOLING (H4DOTC)>THERMOSTAT .
No : Replace the engine coolant temperature sensor. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>ENGINE COOLANT TEMPERATURE SENSOR .